SUSE Linux Enterprise High Availability Extension 12 SP3

Administration Guide

This guide is intended for administrators who need to set up, configure, and maintain clusters with SUSE® Linux Enterprise High Availability Extension. For quick and efficient configuration and administration, the High Availability Extension includes both a graphical user interface (GUI) and a command line interface (CLI). For performing key tasks, both approaches (GUI and CLI) are covered in detail in this guide. Thus, administrators can choose the appropriate tool that matches their needs.

Authors: Tanja Roth and Thomas Schraitle
Publication Date: July 23, 2018
About This Guide
Available Documentation
Feedback
Documentation Conventions
About the Making of This Documentation
I Installation, Setup and Upgrade
1 Product Overview
1.1 Availability as Extension
1.2 Key Features
1.3 Benefits
1.4 Cluster Configurations: Storage
1.5 Architecture
2 System Requirements and Recommendations
2.1 Hardware Requirements
2.2 Software Requirements
2.3 Storage Requirements
2.4 Other Requirements and Recommendations
3 Installing the High Availability Extension
3.1 Manual Installation
3.2 Mass Installation and Deployment with AutoYaST
4 Using the YaST Cluster Module
4.1 Definition of Terms
4.2 YaST Cluster Module
4.3 Defining the Communication Channels
4.4 Defining Authentication Settings
4.5 Transferring the Configuration to All Nodes
4.6 Synchronizing Connection Status Between Cluster Nodes
4.7 Configuring Services
4.8 Bringing the Cluster Online
5 Upgrading Your Cluster and Updating Software Packages
5.1 Terminology
5.2 Upgrading your Cluster to the Latest Product Version
5.3 Updating Software Packages on Cluster Nodes
5.4 For More Information
II Configuration and Administration
6 Configuration and Administration Basics
6.1 Use Case Scenarios
6.2 Quorum Determination
6.3 Cluster Resources
6.4 Resource Monitoring
6.5 Resource Constraints
6.6 Managing Services on Remote Hosts
6.7 Monitoring System Health
6.8 For More Information
7 Configuring and Managing Cluster Resources with Hawk2
7.1 Hawk2 Requirements
7.2 Logging In
7.3 Hawk2 Overview: Main Elements
7.4 Configuring Global Cluster Options
7.5 Configuring Cluster Resources
7.6 Configuring Constraints
7.7 Managing Cluster Resources
7.8 Monitoring Clusters
7.9 Using the Batch Mode
7.10 Viewing the Cluster History
7.11 Verifying Cluster Health
8 Configuring and Managing Cluster Resources (Command Line)
8.1 crmsh—Overview
8.2 Managing Corosync Configuration
8.3 Configuring Global Cluster Options
8.4 Configuring Cluster Resources
8.5 Managing Cluster Resources
8.6 Setting Passwords Independent of cib.xml
8.7 Retrieving History Information
8.8 For More Information
9 Adding or Modifying Resource Agents
9.1 STONITH Agents
9.2 Writing OCF Resource Agents
9.3 OCF Return Codes and Failure Recovery
10 Fencing and STONITH
10.1 Classes of Fencing
10.2 Node Level Fencing
10.3 STONITH Resources and Configuration
10.4 Monitoring Fencing Devices
10.5 Special Fencing Devices
10.6 Basic Recommendations
10.7 For More Information
11 Storage Protection and SBD
11.1 Conceptual Overview
11.2 Overview of Manually Setting Up SBD
11.3 Requirements
11.4 Number of SBD Devices
11.5 Calculation of Timeouts
11.6 Setting Up the Watchdog
11.7 Setting Up SBD with Devices
11.8 Setting Up Diskless SBD
11.9 Testing SBD and Fencing
11.10 Additional Mechanisms for Storage Protection
11.11 For More Information
12 Access Control Lists
12.1 Requirements and Prerequisites
12.2 Enabling Use of ACLs in Your Cluster
12.3 The Basics of ACLs
12.4 Configuring ACLs with Hawk2
12.5 Configuring ACLs with crmsh
13 Network Device Bonding
13.1 Configuring Bonding Devices with YaST
13.2 Hotplugging of Bonding Slaves
13.3 For More Information
14 Load Balancing
14.1 Conceptual Overview
14.2 Configuring Load Balancing with Linux Virtual Server
14.3 Configuring Load Balancing with HAProxy
14.4 For More Information
15 Geo Clusters (Multi-Site Clusters)
16 Executing Maintenance Tasks
16.1 Implications of Taking Down a Cluster Node
16.2 Different Options for Maintenance Tasks
16.3 Preparing and Finishing Maintenance Work
16.4 Putting the Cluster Into Maintenance Mode
16.5 Putting a Node Into Maintenance Mode
16.6 Putting a Node Into Standby Mode
16.7 Putting a Resource Into Maintenance Mode
16.8 Putting a Resource Into Unmanaged Mode
16.9 Rebooting a Cluster Node While In Maintenance Mode
III Storage and Data Replication
17 Distributed Lock Manager (DLM)
17.1 Protocols for DLM Communication
17.2 Configuring DLM Cluster Resources
18 OCFS2
18.1 Features and Benefits
18.2 OCFS2 Packages and Management Utilities
18.3 Configuring OCFS2 Services and a STONITH Resource
18.4 Creating OCFS2 Volumes
18.5 Mounting OCFS2 Volumes
18.6 Configuring OCFS2 Resources With Hawk2
18.7 Using Quotas on OCFS2 File Systems
18.8 For More Information
19 GFS2
19.1 GFS2 Packages and Management Utilities
19.2 Configuring GFS2 Services and a STONITH Resource
19.3 Creating GFS2 Volumes
19.4 Mounting GFS2 Volumes
20 DRBD
20.1 Conceptual Overview
20.2 Installing DRBD Services
20.3 Setting Up DRBD Service
20.4 Migrating from DRBD 8 to DRBD 9
20.5 Creating a Stacked DRBD Device
20.6 Using Resource-Level Fencing
20.7 Testing the DRBD Service
20.8 Tuning DRBD
20.9 Troubleshooting DRBD
20.10 For More Information
21 Cluster Logical Volume Manager (cLVM)
21.1 Conceptual Overview
21.2 Configuration of cLVM
21.3 Configuring Eligible LVM2 Devices Explicitly
21.4 For More Information
22 Cluster Multi-device (Cluster MD)
22.1 Conceptual Overview
22.2 Creating a Clustered MD RAID Device
22.3 Configuring a Resource Agent
22.4 Adding a Device
22.5 Re-adding a Temporarily Failed Device
22.6 Removing a Device
23 Samba Clustering
23.1 Conceptual Overview
23.2 Basic Configuration
23.3 Joining an Active Directory Domain
23.4 Debugging and Testing Clustered Samba
23.5 For More Information
24 Disaster Recovery with Rear (Relax-and-Recover)
24.1 Conceptual Overview
24.2 Setting Up Rear and Your Backup Solution
24.3 Creating the Recovery Installation System
24.4 Testing the Recovery Process
24.5 Recovering from Disaster
24.6 For More Information
IV Appendix
A Troubleshooting
A.1 Installation and First Steps
A.2 Logging
A.3 Resources
A.4 STONITH and Fencing
A.5 History
A.6 Hawk2
A.7 Miscellaneous
A.8 For More Information
B Naming Conventions
C Cluster Management Tools (Command Line)
D Running Cluster Reports Without root Access
D.1 Creating a Local User Account
D.2 Configuring a Passwordless SSH Account
D.3 Configuring sudo
D.4 Generating a Cluster Report
E Documentation Updates
E.1 July 2018 (Maintenance Update of SUSE Linux Enterprise High Availability Extension 12 SP3)
E.2 September 2017 (Initial Release of SUSE Linux Enterprise High Availability Extension 12 SP3)
E.3 April 2017 (Maintenance Update of SUSE Linux Enterprise High Availability Extension 12 SP2)
E.4 March 2017 (Maintenance Update of SUSE Linux Enterprise High Availability Extension 12 SP2)
E.5 November 2016 (Maintenance Update of SUSE Linux Enterprise High Availability Extension 12 SP2)
E.6 November 2016 (Initial Release of SUSE Linux Enterprise High Availability Extension 12 SP2)
E.7 December 2015 (Maintenance Update of SUSE Linux Enterprise High Availability Extension 12 SP1)
E.8 December 2015 (Initial Release of SUSE Linux Enterprise High Availability Extension 12 SP1)
E.9 October 2014 (Initial Release of SUSE Linux Enterprise High Availability Extension 12)
Glossary
F GNU Licenses
F.1 GNU Free Documentation License

Copyright © 2006–2018 SUSE LLC and contributors. All rights reserved.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or (at your option) version 1.3; with the Invariant Section being this copyright notice and license. A copy of the license version 1.2 is included in the section entitled GNU Free Documentation License.

For SUSE trademarks, see http://www.suse.com/company/legal/. All other third-party trademarks are the property of their respective owners. Trademark symbols (®, ™ etc.) denote trademarks of SUSE and its affiliates. Asterisks (*) denote third-party trademarks.

All information found in this book has been compiled with utmost attention to detail. However, this does not guarantee complete accuracy. Neither SUSE LLC, its affiliates, the authors nor the translators shall be held liable for possible errors or the consequences thereof.

About This Guide

Abstract

This guide is intended for administrators who need to set up, configure, and maintain clusters with SUSE® Linux Enterprise High Availability Extension. For quick and efficient configuration and administration, the High Availability Extension includes both a graphical user interface (GUI) and a command line interface (CLI). For performing key tasks, both approaches (GUI and CLI) are covered in detail in this guide. Thus, administrators can choose the appropriate tool that matches their needs.

This guide is divided into the following parts:

Installation, Setup and Upgrade

Before starting to install and configure your cluster, make yourself familiar with cluster fundamentals and architecture, get an overview of the key features and benefits. Learn which hardware and software requirements must be met and what preparations to take before executing the next steps. Perform the installation and basic setup of your HA cluster using YaST. Learn how to upgrade your cluster to the most recent release version or how to update individual packages.

Configuration and Administration

Add, configure and manage cluster resources with either the Web interface (Hawk2), or the command line interface (crmsh). To avoid unauthorized access to the cluster configuration, define roles and assign them to certain users for fine-grained control. Learn how to use load balancing and fencing. If you consider writing your own resource agents or modifying existing ones, get some background information on how to create different types of resource agents.

Storage and Data Replication

SUSE Linux Enterprise High Availability Extension ships with the cluster-aware file systems OCFS2 and GFS2, and the clustered Logical Volume Manager (cLVM). For replication of your data, use DRBD*. It lets you mirror the data of a High Availability service from the active node of a cluster to its standby node. Furthermore, a clustered Samba server also provides a High Availability solution for heterogeneous environments.

Appendix

Contains an overview of common problems and their solution. Presents the naming conventions used in this documentation with regard to clusters, resources and constraints. Shows the published documentation updates including a detailed list of the content changes for each update. Contains a glossary with HA-specific terminology.

Many chapters in this manual contain links to additional documentation resources. These include additional documentation that is available on the system as well as documentation available on the Internet.

For an overview of the documentation available for your product and the latest documentation updates, refer to http://www.suse.com/doc/.

1 Available Documentation

Note
Note: Online Documentation and Latest Updates

Documentation for our products is available at http://www.suse.com/documentation/, where you can also find the latest updates, and browse or download the documentation in various formats. The latest documentation updates can usually be found in the English language version.

In addition, the product documentation is usually available in your installed system under /usr/share/doc/manual.

The following documentation is available for this product:

Administration Guide

This guide is intended for administrators who need to set up, configure, and maintain clusters with SUSE® Linux Enterprise High Availability Extension. For quick and efficient configuration and administration, the High Availability Extension includes both a graphical user interface (GUI) and a command line interface (CLI). For performing key tasks, both approaches (GUI and CLI) are covered in detail in this guide. Thus, administrators can choose the appropriate tool that matches their needs.

Installation and Setup Quick Start

This document guides you through the setup of a very basic two-node cluster, using the bootstrap scripts provided by the ha-cluster-bootstrap package. This includes the configuration of a virtual IP address as a cluster resource and the use of SBD on shared storage as fencing mechanism.

Highly Available NFS Storage with DRBD and Pacemaker

This document describes how to set up highly available NFS storage in a two-node cluster, using the following components of SUSE Linux Enterprise High Availability Extension 12 SP3: DRBD* (Distributed Replicated Block Device), LVM (Logical Volume Manager), and Pacemaker, the cluster resource management framework.

Geo Clustering Quick Start

Geo clustering allows you to have multiple, geographically dispersed sites with a local cluster each. Failover between these clusters is coordinated by a higher level entity: the booth cluster ticket manager.

2 Feedback

Several feedback channels are available:

Bugs and Enhancement Requests

For services and support options available for your product, refer to http://www.suse.com/support/.

To report bugs for a product component, go to https://scc.suse.com/support/requests, log in, and click Create New.

User Comments

We want to hear your comments about and suggestions for this manual and the other documentation included with this product. Use the User Comments feature at the bottom of each page in the online documentation or go to http://www.suse.com/doc/feedback.html and enter your comments there.

Mail

For feedback on the documentation of this product, you can also send a mail to doc-team@suse.com. Make sure to include the document title, the product version and the publication date of the documentation. To report errors or suggest enhancements, provide a concise description of the problem and refer to the respective section number and page (or URL).

3 Documentation Conventions

The following notices and typographical conventions are used in this documentation:

  • tux > command

    Commands that can be run by any user, including the root user.

  • root # command

    Commands that must be run with root privileges. Often you can also prefix these commands with the sudo command to run them.

  • /etc/passwd: directory names and file names

  • PLACEHOLDER: replace PLACEHOLDER with the actual value

  • PATH: the environment variable PATH

  • ls, --help: commands, options, and parameters

  • user: users or groups

  • packagename: name of a package

  • Alt, AltF1: a key to press or a key combination; keys are shown in uppercase as on a keyboard

  • File, File › Save As: menu items, buttons

  • amd64, em64t, ipf This paragraph is only relevant for the architectures amd64, em64t, and ipf. The arrows mark the beginning and the end of the text block.

  • Dancing Penguins (Chapter Penguins, ↑Another Manual): This is a reference to a chapter in another manual.

  • Notices

    Warning
    Warning

    Vital information you must be aware of before proceeding. Warns you about security issues, potential loss of data, damage to hardware, or physical hazards.

    Important
    Important

    Important information you should be aware of before proceeding.

    Note
    Note

    Additional information, for example about differences in software versions.

    Tip
    Tip

    Helpful information, like a guideline or a piece of practical advice.

For an overview of naming conventions with regard to cluster nodes and names, resources, and constraints, see Appendix B, Naming Conventions.

4 About the Making of This Documentation

This documentation is written in SUSEDoc, a subset of DocBook 5. The XML source files were validated by jing (see https://code.google.com/p/jing-trang/), processed by xsltproc, and converted into XSL-FO using a customized version of Norman Walsh's stylesheets. The final PDF is formatted through FOP from Apache Software Foundation. The open source tools and the environment used to build this documentation are provided by the DocBook Authoring and Publishing Suite (DAPS). The project's home page can be found at https://github.com/openSUSE/daps.

The XML source code of this documentation can be found at https://github.com/SUSE/doc-sleha.

Part I Installation, Setup and Upgrade

1 Product Overview

SUSE® Linux Enterprise High Availability Extension is an integrated suite of open source clustering technologies that enables you to implement highly available physical and virtual Linux clusters, and to eliminate single points of failure. It ensures the high availability and manageability of critical network resources including data, applications, and services. Thus, it helps you maintain business continuity, protect data integrity, and reduce unplanned downtime for your mission-critical Linux workloads.

It ships with essential monitoring, messaging, and cluster resource management functionality (supporting failover, failback, and migration (load balancing) of individually managed cluster resources).

This chapter introduces the main product features and benefits of the High Availability Extension. Inside you will find several example clusters and learn about the components making up a cluster. The last section provides an overview of the architecture, describing the individual architecture layers and processes within the cluster.

For explanations of some common terms used in the context of High Availability clusters, refer to Glossary.

2 System Requirements and Recommendations

The following section informs you about system requirements, and some prerequisites for SUSE® Linux Enterprise High Availability Extension. It also includes recommendations for cluster setup.

3 Installing the High Availability Extension

If you are setting up a High Availability cluster with SUSE® Linux Enterprise High Availability Extension for the first time, the easiest way is to start with a basic two-node cluster. You can also use the two-node cluster to run some tests. Afterward, you can add more nodes by cloning existing cluster nodes with AutoYaST. The cloned nodes will have the same packages installed and the same system configuration as the original ones.

If you want to upgrade an existing cluster that runs an older version of SUSE Linux Enterprise High Availability Extension, refer to chapter Chapter 5, Upgrading Your Cluster and Updating Software Packages.

4 Using the YaST Cluster Module

The YaST cluster module allows you to set up a cluster manually (from scratch) or to modify options for an existing cluster.

However, if you prefer an automated approach for setting up a cluster, see the Installation and Setup Quick Start, available from https://www.suse.com/documentation/. It describes how to install the needed packages and leads you to a basic two-node cluster, which is set up with the ha-cluster-bootstrap scripts.

You can also use a combination of both setup methods, for example: set up one node with YaST cluster and then use one of the bootstrap scripts to integrate more nodes (or vice versa).

5 Upgrading Your Cluster and Updating Software Packages

This chapter covers two different scenarios: upgrading a cluster to another version of SUSE Linux Enterprise High Availability Extension (either a major release or a service pack) as opposed to updating individual packages on cluster nodes. See Section 5.2, “Upgrading your Cluster to the Latest Product Version” versus Section 5.3, “Updating Software Packages on Cluster Nodes”.

If you want to upgrade your cluster, check Section 5.2.1, “Supported Upgrade Paths for SLE HA and SLE HA Geo” and Section 5.2.2, “Required Preparations Before Upgrading” before starting to upgrade.

1 Product Overview

Abstract

SUSE® Linux Enterprise High Availability Extension is an integrated suite of open source clustering technologies that enables you to implement highly available physical and virtual Linux clusters, and to eliminate single points of failure. It ensures the high availability and manageability of critical network resources including data, applications, and services. Thus, it helps you maintain business continuity, protect data integrity, and reduce unplanned downtime for your mission-critical Linux workloads.

It ships with essential monitoring, messaging, and cluster resource management functionality (supporting failover, failback, and migration (load balancing) of individually managed cluster resources).

This chapter introduces the main product features and benefits of the High Availability Extension. Inside you will find several example clusters and learn about the components making up a cluster. The last section provides an overview of the architecture, describing the individual architecture layers and processes within the cluster.

For explanations of some common terms used in the context of High Availability clusters, refer to Glossary.

1.1 Availability as Extension

The High Availability Extension is available as an extension to SUSE Linux Enterprise Server 12 SP3. Support for geographically dispersed clusters (Geo clusters) is available as a separate extension to the High Availability Extension, called Geo Clustering for SUSE Linux Enterprise High Availability Extension.

1.2 Key Features

SUSE® Linux Enterprise High Availability Extension helps you ensure and manage the availability of your network resources. The following sections highlight some of the key features:

1.2.1 Wide Range of Clustering Scenarios

The High Availability Extension supports the following scenarios:

  • Active/active configurations

  • Active/passive configurations: N+1, N+M, N to 1, N to M

  • Hybrid physical and virtual clusters, allowing virtual servers to be clustered with physical servers. This improves service availability and resource usage.

  • Local clusters

  • Metro clusters (stretched local clusters)

  • Geo clusters (geographically dispersed clusters)

Your cluster can contain up to 32 Linux servers. Using pacemaker_remote, the cluster can be extended to include additional Linux servers beyond this limit. Any server in the cluster can restart resources (applications, services, IP addresses, and file systems) from a failed server in the cluster.

1.2.2 Flexibility

The High Availability Extension ships with Corosync messaging and membership layer and Pacemaker Cluster Resource Manager. Using Pacemaker, administrators can continually monitor the health and status of their resources, manage dependencies, and automatically stop and start services based on highly configurable rules and policies. The High Availability Extension allows you to tailor a cluster to the specific applications and hardware infrastructure that fit your organization. Time-dependent configuration enables services to automatically migrate back to repaired nodes at specified times.

1.2.3 Storage and Data Replication

With the High Availability Extension you can dynamically assign and reassign server storage as needed. It supports Fibre Channel or iSCSI storage area networks (SANs). Shared disk systems are also supported, but they are not a requirement. SUSE Linux Enterprise High Availability Extension also comes with a cluster-aware file system and volume manager (OCFS2) and the clustered Logical Volume Manager (cLVM). For replication of your data, you can use DRBD* to mirror the data of a High Availability service from the active node of a cluster to its standby node. Furthermore, SUSE Linux Enterprise High Availability Extension also supports CTDB (Clustered Trivial Database), a technology for Samba clustering.

1.2.4 Support for Virtualized Environments

SUSE Linux Enterprise High Availability Extension supports the mixed clustering of both physical and virtual Linux servers. SUSE Linux Enterprise Server 12 SP3 ships with Xen, an open source virtualization hypervisor and with KVM (Kernel-based Virtual Machine), a virtualization software for Linux which is based on hardware virtualization extensions. The cluster resource manager in the High Availability Extension can recognize, monitor, and manage services running within virtual servers, as well as services running in physical servers. Guest systems can be managed as services by the cluster.

1.2.5 Support of Local, Metro, and Geo Clusters

SUSE Linux Enterprise High Availability Extension has been extended to support different geographical scenarios. Support for geographically dispersed clusters (Geo clusters) is available as a separate extension to High Availability Extension, called Geo Clustering for SUSE Linux Enterprise High Availability Extension.

Local Clusters

A single cluster in one location (for example, all nodes are located in one data center). The cluster uses multicast or unicast for communication between the nodes and manages failover internally. Network latency can be neglected. Storage is typically accessed synchronously by all nodes.

Metro Clusters

A single cluster that can stretch over multiple buildings or data centers, with all sites connected by fibre channel. The cluster uses multicast or unicast for communication between the nodes and manages failover internally. Network latency is usually low (<5 ms for distances of approximately 20 miles). Storage is frequently replicated (mirroring or synchronous replication).

Geo Clusters (Multi-Site Clusters)

Multiple, geographically dispersed sites with a local cluster each. The sites communicate via IP. Failover across the sites is coordinated by a higher-level entity. Geo clusters need to cope with limited network bandwidth and high latency. Storage is replicated asynchronously.

The greater the geographical distance between individual cluster nodes, the more factors may potentially disturb the high availability of services the cluster provides. Network latency, limited bandwidth and access to storage are the main challenges for long-distance clusters.

1.2.6 Resource Agents

SUSE Linux Enterprise High Availability Extension includes a huge number of resource agents to manage resources such as Apache, IPv4, IPv6 and many more. It also ships with resource agents for popular third party applications such as IBM WebSphere Application Server. For an overview of Open Cluster Framework (OCF) resource agents included with your product, use the crm ra command as described in Section 8.1.3, “Displaying Information about OCF Resource Agents”.

1.2.7 User-friendly Administration Tools

The High Availability Extension ships with a set of powerful tools for basic installation and setup of your cluster as well as effective configuration and administration:

YaST

A graphical user interface for general system installation and administration. Use it to install the High Availability Extension on top of SUSE Linux Enterprise Server as described in the Installation and Setup Quick Start. YaST also provides the following modules in the High Availability category to help configure your cluster or individual components:

HA Web Konsole (Hawk2)

A Web-based user interface with which you can administer your Linux cluster from non-Linux machines. It is also an ideal solution in case your system does not provide a graphical user interface. It guides you through the creation and configuration of resources and lets you execute management tasks like starting, stopping or migrating resources. For details, refer to Chapter 7, Configuring and Managing Cluster Resources with Hawk2.

crm Shell

A powerful unified command line interface to configure resources and execute all monitoring or administration tasks. For details, refer to Chapter 8, Configuring and Managing Cluster Resources (Command Line).

1.3 Benefits

The High Availability Extension allows you to configure up to 32 Linux servers into a high-availability cluster (HA cluster), where resources can be dynamically switched or moved to any server in the cluster. Resources can be configured to automatically migrate if a server fails, or they can be moved manually to troubleshoot hardware or balance the workload.

The High Availability Extension provides high availability from commodity components. Lower costs are obtained through the consolidation of applications and operations onto a cluster. The High Availability Extension also allows you to centrally manage the complete cluster and to adjust resources to meet changing workload requirements (thus, manually load balance the cluster). Allowing clusters of more than two nodes also provides savings by allowing several nodes to share a hot spare.

An equally important benefit is the potential reduction of unplanned service outages as well as planned outages for software and hardware maintenance and upgrades.

Reasons that you would want to implement a cluster include:

  • Increased availability

  • Improved performance

  • Low cost of operation

  • Scalability

  • Disaster recovery

  • Data protection

  • Server consolidation

  • Storage consolidation

Shared disk fault tolerance can be obtained by implementing RAID on the shared disk subsystem.

The following scenario illustrates some benefits the High Availability Extension can provide.

Example Cluster Scenario

Suppose you have configured a three-server cluster, with a Web server installed on each of the three servers in the cluster. Each of the servers in the cluster hosts two Web sites. All the data, graphics, and Web page content for each Web site are stored on a shared disk subsystem connected to each of the servers in the cluster. The following figure depicts how this setup might look.

Three-Server Cluster
Figure 1.1: Three-Server Cluster

During normal cluster operation, each server is in constant communication with the other servers in the cluster and performs periodic polling of all registered resources to detect failure.

Suppose Web Server 1 experiences hardware or software problems and the users depending on Web Server 1 for Internet access, e-mail, and information lose their connections. The following figure shows how resources are moved when Web Server 1 fails.

Three-Server Cluster after One Server Fails
Figure 1.2: Three-Server Cluster after One Server Fails

Web Site A moves to Web Server 2 and Web Site B moves to Web Server 3. IP addresses and certificates also move to Web Server 2 and Web Server 3.

When you configured the cluster, you decided where the Web sites hosted on each Web server would go should a failure occur. In the previous example, you configured Web Site A to move to Web Server 2 and Web Site B to move to Web Server 3. This way, the workload once handled by Web Server 1 continues to be available and is evenly distributed between any surviving cluster members.

When Web Server 1 failed, the High Availability Extension software did the following:

  • Detected a failure and verified with STONITH that Web Server 1 was really dead. STONITH is an acronym for Shoot The Other Node In The Head and is a means of bringing down misbehaving nodes to prevent them from causing trouble in the cluster.

  • Remounted the shared data directories that were formerly mounted on Web server 1 on Web Server 2 and Web Server 3.

  • Restarted applications that were running on Web Server 1 on Web Server 2 and Web Server 3.

  • Transferred IP addresses to Web Server 2 and Web Server 3.

In this example, the failover process happened quickly and users regained access to Web site information within seconds, usually without needing to log in again.

Now suppose the problems with Web Server 1 are resolved, and Web Server 1 is returned to a normal operating state. Web Site A and Web Site B can either automatically fail back (move back) to Web Server 1, or they can stay where they are. This depends on how you configured the resources for them. Migrating the services back to Web Server 1 will incur some down-time, so the High Availability Extension also allows you to defer the migration until a period when it will cause little or no service interruption. There are advantages and disadvantages to both alternatives.

The High Availability Extension also provides resource migration capabilities. You can move applications, Web sites, etc. to other servers in your cluster as required for system management.

For example, you could have manually moved Web Site A or Web Site B from Web Server 1 to either of the other servers in the cluster. Use cases for this are upgrading or performing scheduled maintenance on Web Server 1, or increasing performance or accessibility of the Web sites.

1.4 Cluster Configurations: Storage

Cluster configurations with the High Availability Extension might or might not include a shared disk subsystem. The shared disk subsystem can be connected via high-speed Fibre Channel cards, cables, and switches, or it can be configured to use iSCSI. If a server fails, another designated server in the cluster automatically mounts the shared disk directories that were previously mounted on the failed server. This gives network users continuous access to the directories on the shared disk subsystem.

Important
Important: Shared Disk Subsystem with cLVM

When using a shared disk subsystem with cLVM, that subsystem must be connected to all servers in the cluster from which it needs to be accessed.

Typical resources might include data, applications, and services. The following figure shows how a typical Fibre Channel cluster configuration might look.

Typical Fibre Channel Cluster Configuration
Figure 1.3: Typical Fibre Channel Cluster Configuration

Although Fibre Channel provides the best performance, you can also configure your cluster to use iSCSI. iSCSI is an alternative to Fibre Channel that can be used to create a low-cost Storage Area Network (SAN). The following figure shows how a typical iSCSI cluster configuration might look.

Typical iSCSI Cluster Configuration
Figure 1.4: Typical iSCSI Cluster Configuration

Although most clusters include a shared disk subsystem, it is also possible to create a cluster without a shared disk subsystem. The following figure shows how a cluster without a shared disk subsystem might look.

Typical Cluster Configuration Without Shared Storage
Figure 1.5: Typical Cluster Configuration Without Shared Storage

1.5 Architecture

This section provides a brief overview of the High Availability Extension architecture. It identifies and provides information on the architectural components, and describes how those components interoperate.

1.5.1 Architecture Layers

The High Availability Extension has a layered architecture. Figure 1.6, “Architecture” illustrates the different layers and their associated components.

Architecture
Figure 1.6: Architecture

1.5.1.1 Messaging and Infrastructure Layer

The primary or first layer is the messaging/infrastructure layer, also known as the Corosync layer. This layer contains components that send out the messages containing I'm alive signals, as well as other information.

1.5.1.2 Resource Allocation Layer

The next layer is the resource allocation layer. This layer is the most complex, and consists of the following components:

Cluster Resource Manager (CRM)

Every action taken in the resource allocation layer passes through the Cluster Resource Manager. If other components of the resource allocation layer (or components which are in a higher layer) need to communicate, they do so through the local CRM. On every node, the CRM maintains the Cluster Information Base (CIB).

Cluster Information Base (CIB)

The Cluster Information Base is an in-memory XML representation of the entire cluster configuration and current status. It contains definitions of all cluster options, nodes, resources, constraints and the relationship to each other. The CIB also synchronizes updates to all cluster nodes. There is one master CIB in the cluster, maintained by the Designated Coordinator (DC). All other nodes contain a CIB replica.

Designated Coordinator (DC)

One CRM in the cluster is elected as DC. The DC is the only entity in the cluster that can decide that a cluster-wide change needs to be performed, such as fencing a node or moving resources around. The DC is also the node where the master copy of the CIB is kept. All other nodes get their configuration and resource allocation information from the current DC. The DC is elected from all nodes in the cluster after a membership change.

Policy Engine (PE)

Whenever the Designated Coordinator needs to make a cluster-wide change (react to a new CIB), the Policy Engine calculates the next state of the cluster based on the current state and configuration. The PE also produces a transition graph containing a list of (resource) actions and dependencies to achieve the next cluster state. The PE always runs on the DC.

Local Resource Manager (LRM)

The LRM calls the local Resource Agents (see Section 1.5.1.3, “Resource Layer”) on behalf of the CRM. It can thus perform start / stop / monitor operations and report the result to the CRM. The LRM is the authoritative source for all resource-related information on its local node.

1.5.1.3 Resource Layer

The highest layer is the Resource Layer. The Resource Layer includes one or more Resource Agents (RA). Resource Agents are programs (usually shell scripts) that have been written to start, stop, and monitor a certain kind of service (a resource). Resource Agents are called only by the LRM. Third parties can include their own agents in a defined location in the file system and thus provide out-of-the-box cluster integration for their own software.

1.5.2 Process Flow

SUSE Linux Enterprise High Availability Extension uses Pacemaker as CRM. The CRM is implemented as daemon (crmd) that has an instance on each cluster node. Pacemaker centralizes all cluster decision-making by electing one of the crmd instances to act as a master. Should the elected crmd process (or the node it is on) fail, a new one is established.

A CIB, reflecting the cluster’s configuration and current state of all resources in the cluster is kept on each node. The contents of the CIB are automatically kept synchronous across the entire cluster.

Many actions performed in the cluster will cause a cluster-wide change. These actions can include things like adding or removing a cluster resource or changing resource constraints. It is important to understand what happens in the cluster when you perform such an action.

For example, suppose you want to add a cluster IP address resource. To do this, you can use one of the command line tools or the Web interface to modify the CIB. It is not required to perform the actions on the DC, you can use either tool on any node in the cluster and they will be relayed to the DC. The DC will then replicate the CIB change to all cluster nodes.

Based on the information in the CIB, the PE then computes the ideal state of the cluster and how it should be achieved and feeds a list of instructions to the DC. The DC sends commands via the messaging/infrastructure layer which are received by the crmd peers on other nodes. Each crmd uses its LRM (implemented as lrmd) to perform resource modifications. The lrmd is not cluster-aware and interacts directly with resource agents (scripts).

All peer nodes report the results of their operations back to the DC. After the DC concludes that all necessary operations are successfully performed in the cluster, the cluster will go back to the idle state and wait for further events. If any operation was not carried out as planned, the PE is invoked again with the new information recorded in the CIB.

In some cases, it may be necessary to power off nodes to protect shared data or complete resource recovery. For this Pacemaker comes with a fencing subsystem, stonithd. STONITH is an acronym for Shoot The Other Node In The Head and is usually implemented with a remote power switch. In Pacemaker, STONITH devices are modeled as resources (and configured in the CIB) to enable them to be easily monitored for failure. However, stonithd takes care of understanding the STONITH topology such that its clients simply request a node be fenced and it does the rest.

2 System Requirements and Recommendations

Abstract

The following section informs you about system requirements, and some prerequisites for SUSE® Linux Enterprise High Availability Extension. It also includes recommendations for cluster setup.

2.1 Hardware Requirements

The following list specifies hardware requirements for a cluster based on SUSE® Linux Enterprise High Availability Extension. These requirements represent the minimum hardware configuration. Additional hardware might be necessary, depending on how you intend to use your cluster.

Servers

1 to 32 Linux servers with software as specified in Section 2.2, “Software Requirements”.

The servers can be bare metal or virtual machines. They do not require identical hardware (memory, disk space, etc.), but they must have the same architecture. Cross-platform clusters are not supported.

Using pacemaker_remote, the cluster can be extended to include additional Linux servers beyond the 32-node limit.

Communication Channels

At least two TCP/IP communication media per cluster node. The network equipment must support the communication means you want to use for cluster communication: multicast or unicast. The communication media should support a data rate of 100 Mbit/s or higher. For a supported cluster setup two or more redundant communication paths are required. This can be done via:

  • Network Device Bonding (to be preferred).

  • A second communication channel in Corosync.

For details, refer to Chapter 13, Network Device Bonding and Procedure 4.3, “Defining a Redundant Communication Channel”, respectively.

Node Fencing/STONITH

To avoid a split brain scenario, clusters need a node fencing mechanism. In a split brain scenario, cluster nodes are divided into two or more groups that do not know about each other (due to a hardware or software failure or due to a cut network connection). A fencing mechanism isolates the node in question (usually by resetting or powering off the node). This is also called STONITH (Shoot the other node in the head). A node fencing mechanism can be either a physical device (a power switch) or a mechanism like SBD (STONITH by disk) in combination with a watchdog. Using SBD requires shared storage.

Unless SBD is used, each node in the High Availability cluster must have at least one STONITH device. We strongly recommend multiple STONITH devices per node.

Important
Important: No Support Without STONITH
  • You must have a node fencing mechanism for your cluster.

  • The global cluster options stonith-enabled and startup-fencing must be set to true. When you change them, you lose support.

2.2 Software Requirements

On all nodes that will be part of the cluster the following software must be installed.

  • SUSE® Linux Enterprise Server 12 SP3 (with all available online updates)

  • SUSE Linux Enterprise High Availability Extension 12 SP3 (with all available online updates)

  • (Optional) For Geo clusters: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 SP3 (with all available online updates)

2.3 Storage Requirements

Some services require shared storage. If using an external NFS share, it must be reliably accessible from all cluster nodes via redundant communication paths.

To make data highly available, a shared disk system (Storage Area Network, or SAN) is recommended for your cluster. If a shared disk subsystem is used, ensure the following:

  • The shared disk system is properly set up and functional according to the manufacturer’s instructions.

  • The disks contained in the shared disk system should be configured to use mirroring or RAID to add fault tolerance to the shared disk system. Hardware-based RAID is recommended. Host-based software RAID is not supported for all configurations.

  • If you are using iSCSI for shared disk system access, ensure that you have properly configured iSCSI initiators and targets.

  • When using DRBD* to implement a mirroring RAID system that distributes data across two machines, make sure to only access the device provided by DRBD—never the backing device. Use the same (bonded) NICs that the rest of the cluster uses to leverage the redundancy provided there.

When using SBD as STONITH mechanism, additional requirements apply for the shared storage. For details, see Section 11.3, “Requirements”.

2.4 Other Requirements and Recommendations

For a supported and useful High Availability setup, consider the following recommendations:

Number of Cluster Nodes

For clusters with more than two nodes, it is strongly recommended to use an odd number of cluster nodes to have quorum. For more information about quorum, see Section 6.2, “Quorum Determination”.

Time Synchronization

Cluster nodes must synchronize to an NTP server outside the cluster. For more information, see the Administration Guide for SUSE Linux Enterprise Server 12 SP3: http://www.suse.com/documentation/sles-12/book_sle_admin/data/cha_netz_xntp.html.

If nodes are not synchronized, the cluster may not work properly. In addition, log files and cluster reports are very hard to analyze without synchronization. If you use the bootstrap scripts, you will be warned if NTP is not configured yet.

Network Interface Card (NIC) Names

Must be identical on all nodes.

Host Name and IP Address
SSH

All cluster nodes must be able to access each other via SSH. Tools like crm report (for troubleshooting) and Hawk2's History Explorer require passwordless SSH access between the nodes, otherwise they can only collect data from the current node.

Note
Note: Regulatory Requirements

If passwordless SSH access does not comply with regulatory requirements, you can use the work-around described in Appendix D, Running Cluster Reports Without root Access for running crm report.

For the History Explorer there is currently no alternative for passwordless login.

3 Installing the High Availability Extension

Abstract

If you are setting up a High Availability cluster with SUSE® Linux Enterprise High Availability Extension for the first time, the easiest way is to start with a basic two-node cluster. You can also use the two-node cluster to run some tests. Afterward, you can add more nodes by cloning existing cluster nodes with AutoYaST. The cloned nodes will have the same packages installed and the same system configuration as the original ones.

If you want to upgrade an existing cluster that runs an older version of SUSE Linux Enterprise High Availability Extension, refer to chapter Chapter 5, Upgrading Your Cluster and Updating Software Packages.

3.1 Manual Installation

The manual installation of the packages for High Availability Extension is described in Installation and Setup Quick Start. It leads you through the setup of a basic two-node cluster. Find it at https://www.suse.com/documentation/.

3.2 Mass Installation and Deployment with AutoYaST

After you have installed and set up a two-node cluster, you can extend the cluster by cloning existing nodes with AutoYaST and adding the clones to the cluster.

AutoYaST uses profiles that contains installation and configuration data. A profile tells AutoYaST what to install and how to configure the installed system to get a ready-to-use system in the end. This profile can then be used for mass deployment in different ways (for example, to clone existing cluster nodes).

For detailed instructions on how to use AutoYaST in various scenarios, see the SUSE Linux Enterprise 12 SP3 Deployment Guide, available at http://www.suse.com/documentation/sle-12. Refer to chapter Automated Installation.

Important
Important: Identical Hardware

Procedure 3.1, “Cloning a Cluster Node with AutoYaST” assumes you are rolling out SUSE Linux Enterprise High Availability Extension 12 SP3 to a set of machines with identical hardware configurations.

If you need to deploy cluster nodes on non-identical hardware, refer to the SUSE Linux Enterprise 12 SP3 Deployment Guide, chapter Automated Installation, section Rule-Based Autoinstallation.

Procedure 3.1: Cloning a Cluster Node with AutoYaST
  1. Make sure the node you want to clone is correctly installed and configured. For details, see the Installation and Setup Quick Start for SUSE Linux Enterprise High Availability Extension or Chapter 4, Using the YaST Cluster Module.

  2. Follow the description outlined in the SUSE Linux Enterprise 12 SP3 Deployment Guide for simple mass installation. This includes the following basic steps:

    1. Creating an AutoYaST profile. Use the AutoYaST GUI to create and modify a profile based on the existing system configuration. In AutoYaST, choose the High Availability module and click the Clone button. If needed, adjust the configuration in the other modules and save the resulting control file as XML.

      If you have configured DRBD, you can select and clone this module in the AutoYaST GUI, too.

    2. Determining the source of the AutoYaST profile and the parameter to pass to the installation routines for the other nodes.

    3. Determining the source of the SUSE Linux Enterprise Server and SUSE Linux Enterprise High Availability Extension installation data.

    4. Determining and setting up the boot scenario for autoinstallation.

    5. Passing the command line to the installation routines, either by adding the parameters manually or by creating an info file.

    6. Starting and monitoring the autoinstallation process.

After the clone has been successfully installed, execute the following steps to make the cloned node join the cluster:

Procedure 3.2: Bringing the Cloned Node Online
  1. Transfer the key configuration files from the already configured nodes to the cloned node with Csync2 as described in Section 4.5, “Transferring the Configuration to All Nodes”.

  2. To bring the node online, start the Pacemaker service on the cloned node as described in Section 4.8, “Bringing the Cluster Online”.

The cloned node will now join the cluster because the /etc/corosync/corosync.conf file has been applied to the cloned node via Csync2. The CIB is automatically synchronized among the cluster nodes.

4 Using the YaST Cluster Module

Abstract

The YaST cluster module allows you to set up a cluster manually (from scratch) or to modify options for an existing cluster.

However, if you prefer an automated approach for setting up a cluster, see the Installation and Setup Quick Start, available from https://www.suse.com/documentation/. It describes how to install the needed packages and leads you to a basic two-node cluster, which is set up with the ha-cluster-bootstrap scripts.

You can also use a combination of both setup methods, for example: set up one node with YaST cluster and then use one of the bootstrap scripts to integrate more nodes (or vice versa).

4.1 Definition of Terms

Several key terms used in the YaST cluster module and in this chapter are defined below.

Bind Network Address (bindnetaddr)

The network address the Corosync executive should bind to. To simplify sharing configuration files across the cluster, Corosync uses network interface netmask to mask only the address bits that are used for routing the network. For example, if the local interface is 192.168.5.92 with netmask 255.255.255.0, set bindnetaddr to 192.168.5.0. If the local interface is 192.168.5.92 with netmask 255.255.255.192, set bindnetaddr to 192.168.5.64.

Note
Note: Network Address for All Nodes

As the same Corosync configuration will be used on all nodes, make sure to use a network address as bindnetaddr, not the address of a specific network interface.

conntrack Tools

Allow interaction with the in-kernel connection tracking system for enabling stateful packet inspection for iptables. Used by the High Availability Extension to synchronize the connection status between cluster nodes. For detailed information, refer to http://conntrack-tools.netfilter.org/.

Csync2

A synchronization tool that can be used to replicate configuration files across all nodes in the cluster, and even across Geo clusters. Csync2 can handle any number of hosts, sorted into synchronization groups. Each synchronization group has its own list of member hosts and its include/exclude patterns that define which files should be synchronized in the synchronization group. The groups, the host names belonging to each group, and the include/exclude rules for each group are specified in the Csync2 configuration file, /etc/csync2/csync2.cfg.

For authentication, Csync2 uses the IP addresses and pre-shared keys within a synchronization group. You need to generate one key file for each synchronization group and copy it to all group members.

For more information about Csync2, refer to http://oss.linbit.com/csync2/paper.pdf

Existing Cluster

The term existing cluster is used to refer to any cluster that consists of at least one node. Existing clusters have a basic Corosync configuration that defines the communication channels, but they do not necessarily have resource configuration yet.

Multicast

A technology used for a one-to-many communication within a network that can be used for cluster communication. Corosync supports both multicast and unicast. If multicast does not comply with your corporate IT policy, use unicast instead.

Note
Note: Switches and Multicast

If you want to use multicast for cluster communication, make sure your switches support multicast.

Multicast Address (mcastaddr)

IP address to be used for multicasting by the Corosync executive. The IP address can either be IPv4 or IPv6. If IPv6 networking is used, node IDs must be specified. You can use any multicast address in your private network.

Multicast Port (mcastport)

The port to use for cluster communication. Corosync uses two ports: the specified mcastport for receiving multicast, and mcastport -1 for sending multicast.

Redundant Ring Protocol (RRP)

Allows the use of multiple redundant local area networks for resilience against partial or total network faults. This way, cluster communication can still be kept up as long as a single network is operational. Corosync supports the Totem Redundant Ring Protocol. A logical token-passing ring is imposed on all participating nodes to deliver messages in a reliable and sorted manner. A node is allowed to broadcast a message only if it holds the token. For more information, refer to http://www.rcsc.de/pdf/icdcs02.pdf.

When having defined redundant communication channels in Corosync, use RRP to tell the cluster how to use these interfaces. RRP can have three modes (rrp_mode):

  • If set to active, Corosync uses both interfaces actively.

  • If set to passive, Corosync sends messages alternatively over the available networks.

  • If set to none, RRP is disabled.

Unicast

A technology for sending messages to a single network destination. Corosync supports both multicast and unicast. In Corosync, unicast is implemented as UDP-unicast (UDPU).

4.2 YaST Cluster Module

Start YaST and select High Availability › Cluster. Alternatively, start the module from command line:

sudo yast2 cluster

The following list shows an overview of the available screens in the YaST cluster module. It also mentions whether the screen contains parameters that are required for successful cluster setup or whether its parameters are optional.

Communication Channels (required)

Allows you to define one or two communication channels for communication between the cluster nodes. As transport protocol, either use multicast (UDP) or unicast (UDPU). For details, see Section 4.3, “Defining the Communication Channels”.

Important
Important: Redundant Communication Paths

For a supported cluster setup two or more redundant communication paths are required. The preferred way is to use network device bonding as described in Chapter 13, Network Device Bonding.

If this is impossible, you need to define a second communication channel in Corosync.

Security (optional but recommended)

Allows you to define the authentication settings for the cluster. HMAC/SHA1 authentication requires a shared secret used to protect and authenticate messages. For details, see Section 4.4, “Defining Authentication Settings”.

Configure Csync2 (optional but recommended)

Csync2 helps you to keep track of configuration changes and to keep files synchronized across the cluster nodes. For details, see Section 4.5, “Transferring the Configuration to All Nodes”.

Configure conntrackd (optional)

Allows you to configure the user-space conntrackd. Use the conntrack tools for stateful packet inspection for iptables. For details, see Section 4.6, “Synchronizing Connection Status Between Cluster Nodes”.

Service (required)

Allows you to configure the service for bringing the cluster node online. Define whether to start the Pacemaker service at boot time and whether to open the ports in the firewall that are needed for communication between the nodes. For details, see Section 4.7, “Configuring Services”.

If you start the cluster module for the first time, it appears as a wizard, guiding you through all the steps necessary for basic setup. Otherwise, click the categories on the left panel to access the configuration options for each step.

Note
Note: Settings in the YaST Cluster Module

Some settings in the YaST cluster module apply only to the current node. Other settings may automatically be transferred to all nodes with Csync2. Find detailed information about this in the following sections.

4.3 Defining the Communication Channels

For successful communication between the cluster nodes, define at least one communication channel. As transport protocol, either use multicast (UDP) or unicast (UDPU) as described in Procedure 4.1 or Procedure 4.2, respectively. If you want to define a second, redundant channel (Procedure 4.3), both communication channels must use the same protocol.

All settings defined in the YaST Communication Channels screen are written to /etc/corosync/corosync.conf. Find example files for a multicast and a unicast setup in /usr/share/doc/packages/corosync/.

If you are using IPv4 addresses, node IDs are optional. If you are using IPv6 addresses, node IDs are required. Instead of specifying IDs manually for each node, the YaST cluster module contains an option to automatically generate a unique ID for every cluster node.

Procedure 4.1: Defining the First Communication Channel (Multicast)

When using multicast, the same bindnetaddr, mcastaddr, and mcastport will be used for all cluster nodes. All nodes in the cluster will know each other by using the same multicast address. For different clusters, use different multicast addresses.

  1. Start the YaST cluster module and switch to the Communication Channels category.

  2. Set the Transport protocol to Multicast.

  3. Define the Bind Network Address. Set the value to the subnet you will use for cluster multicast.

  4. Define the Multicast Address.

  5. Define the Multicast Port.

  6. To automatically generate a unique ID for every cluster node keep Auto Generate Node ID enabled.

  7. Define a Cluster Name.

  8. Enter the number of Expected Votes. This is important for Corosync to calculate quorum in case of a partitioned cluster. By default, each node has 1 vote. The number of Expected Votes must match the number of nodes in your cluster.

  9. Confirm your changes.

  10. If needed, define a redundant communication channel in Corosync as described in Procedure 4.3, “Defining a Redundant Communication Channel”.

YaST Cluster—Multicast Configuration
Figure 4.1: YaST Cluster—Multicast Configuration

If you want to use unicast instead of multicast for cluster communication, proceed as follows.

Procedure 4.2: Defining the First Communication Channel (Unicast)
  1. Start the YaST cluster module and switch to the Communication Channels category.

  2. Set the Transport protocol to Unicast.

  3. Define the Multicast Port.

  4. For unicast communication, Corosync needs to know the IP addresses of all nodes in the cluster. For each node that will be part of the cluster, click Add and enter the following details:

    • IP Address

    • Redundant IP Address (only required if you use a second communication channel in Corosync)

    • Node ID (only required if the option Auto Generate Node ID is disabled)

    To modify or remove any addresses of cluster members, use the Edit or Del buttons.

  5. To automatically generate a unique ID for every cluster node keep Auto Generate Node ID enabled.

  6. Define a Cluster Name.

  7. Enter the number of Expected Votes. This is important for Corosync to calculate quorum in case of a partitioned cluster. By default, each node has 1 vote. The number of Expected Votes must match the number of nodes in your cluster.

  8. Confirm your changes.

  9. If needed, define a redundant communication channel in Corosync as described in Procedure 4.3, “Defining a Redundant Communication Channel”.

YaST Cluster—Unicast Configuration
Figure 4.2: YaST Cluster—Unicast Configuration

If network device bonding cannot be used for any reason, the second best choice is to define a redundant communication channel (a second ring) in Corosync. That way, two physically separate networks can be used for communication. If one network fails, the cluster nodes can still communicate via the other network.

The additional communication channel in Corosync will form a second token-passing ring. In /etc/corosync/corosync.conf, the first channel you configured is the primary ring and gets the ringnumber 0. The second ring (redundant channel) gets the ringnumber 1.

When having defined redundant communication channels in Corosync, use RRP to tell the cluster how to use these interfaces. With RRP, two physically separate networks are used for communication. If one network fails, the cluster nodes can still communicate via the other network.

RRP can have three modes:

  • If set to active, Corosync uses both interfaces actively.

  • If set to passive, Corosync sends messages alternatively over the available networks.

  • If set to none, RRP is disabled.

Procedure 4.3: Defining a Redundant Communication Channel
Important
Important: Redundant Rings and /etc/hosts

If multiple rings are configured in Corosync, each node can have multiple IP addresses. This needs to be reflected in the /etc/hosts file of all nodes.

  1. Start the YaST cluster module and switch to the Communication Channels category.

  2. Activate Redundant Channel. The redundant channel must use the same protocol as the first communication channel you defined.

  3. If you use multicast, enter the following parameters: the Bind Network Address to use, the Multicast Address and the Multicast Port for the redundant channel.

    If you use unicast, define the following parameters: the Bind Network Address to use, and the Multicast Port. Enter the IP addresses of all nodes that will be part of the cluster.

  4. To tell Corosync how and when to use the different channels, select the rrp_mode to use:

    • If only one communication channel is defined, rrp_mode is automatically disabled (value none).

    • If set to active, Corosync uses both interfaces actively.

    • If set to passive, Corosync sends messages alternatively over the available networks.

    As soon as RRP is used, the High Availability Extension monitors the status of the current rings and automatically re-enables redundant rings after faults.

    Alternatively, check the ring status manually with corosync-cfgtool. View the available options with -h.

  5. Confirm your changes.

4.4 Defining Authentication Settings

To define the authentication settings for the cluster, you can use HMAC/SHA1 authentication. This requires a shared secret used to protect and authenticate messages. The authentication key (password) you specify will be used on all nodes in the cluster.

Procedure 4.4: Enabling Secure Authentication
  1. Start the YaST cluster module and switch to the Security category.

  2. Activate Enable Security Auth.

  3. For a newly created cluster, click Generate Auth Key File. An authentication key is created and written to /etc/corosync/authkey.

    If you want the current machine to join an existing cluster, do not generate a new key file. Instead, copy the /etc/corosync/authkey from one of the nodes to the current machine (either manually or with Csync2).

  4. Confirm your changes. YaST writes the configuration to /etc/corosync/corosync.conf.

YaST Cluster—Security
Figure 4.3: YaST Cluster—Security

4.5 Transferring the Configuration to All Nodes

Instead of copying the resulting configuration files to all nodes manually, use the csync2 tool for replication across all nodes in the cluster.

This requires the following basic steps:

Csync2 helps you to keep track of configuration changes and to keep files synchronized across the cluster nodes:

  • You can define a list of files that are important for operation.

  • You can show changes to these files (against the other cluster nodes).

  • You can synchronize the configured files with a single command.

  • With a simple shell script in ~/.bash_logout, you can be reminded about unsynchronized changes before logging out of the system.

Find detailed information about Csync2 at http://oss.linbit.com/csync2/ and http://oss.linbit.com/csync2/paper.pdf.

4.5.1 Configuring Csync2 with YaST

  1. Start the YaST cluster module and switch to the Csync2 category.

  2. To specify the synchronization group, click Add in the Sync Host group and enter the local host names of all nodes in your cluster. For each node, you must use exactly the strings that are returned by the hostname command.

    Tip
    Tip: Host Name Resolution

    If host name resolution does not work properly in your network, you can also specify a combination of host name and IP address for each cluster node. To do so, use the string HOSTNAME@IP such as alice@192.168.2.100, for example. Csync2 will then use the IP addresses when connecting.

  3. Click Generate Pre-Shared-Keys to create a key file for the synchronization group. The key file is written to /etc/csync2/key_hagroup. After it has been created, it must be copied manually to all members of the cluster.

  4. To populate the Sync File list with the files that usually need to be synchronized among all nodes, click Add Suggested Files.

  5. If you want to Edit, Add or Remove files from the list of files to be synchronized use the respective buttons. You must enter the absolute path name for each file.

  6. Activate Csync2 by clicking Turn Csync2 ON. This will execute the following command to start Csync2 automatically at boot time:

    root # systemctl enable csync2.socket
  7. Confirm your changes. YaST writes the Csync2 configuration to /etc/csync2/csync2.cfg.

  8. To start the synchronization process now, proceed with Section 4.5.2, “Synchronizing Changes with Csync2”.

YaST Cluster—Csync2
Figure 4.4: YaST Cluster—Csync2

4.5.2 Synchronizing Changes with Csync2

To successfully synchronize the files with Csync2, the following requirements must be met:

  • The same Csync2 configuration is available on all cluster nodes.

  • The same Csync2 authentication key is available on all cluster nodes.

  • Csync2 must be running on all cluster nodes.

Before the first Csync2 run, you therefore need to make the following preparations:

Procedure 4.5: Preparing for Initial Synchronization with Csync2
  1. Copy the file /etc/csync2/csync2.cfg manually to all nodes after you have configured it as described in Section 4.5.1, “Configuring Csync2 with YaST”.

  2. Copy the file /etc/csync2/key_hagroup that you have generated on one node in Step 3 of Section 4.5.1 to all nodes in the cluster. It is needed for authentication by Csync2. However, do not regenerate the file on the other nodes—it needs to be the same file on all nodes.

  3. Execute the following command on all nodes to start the service now:

    root # systemctl start csync2.socket
Procedure 4.6: Synchronizing the Configuration Files with Csync2
  1. To initially synchronize all files once, execute the following command on the machine that you want to copy the configuration from:

    root # csync2 -xv

    This will synchronize all the files once by pushing them to the other nodes. If all files are synchronized successfully, Csync2 will finish with no errors.

    If one or several files that are to be synchronized have been modified on other nodes (not only on the current one), Csync2 reports a conflict. You will get an output similar to the one below:

    While syncing file /etc/corosync/corosync.conf:
    ERROR from peer hex-14: File is also marked dirty here!
    Finished with 1 errors.
  2. If you are sure that the file version on the current node is the best one, you can resolve the conflict by forcing this file and resynchronizing:

    root # csync2 -f /etc/corosync/corosync.conf
    root # csync2 -x

For more information on the Csync2 options, run

csync2 -help
Note
Note: Pushing Synchronization After Any Changes

Csync2 only pushes changes. It does not continuously synchronize files between the machines.

Each time you update files that need to be synchronized, you need to push the changes to the other machines: Run csync2  -xv on the machine where you did the changes. If you run the command on any of the other machines with unchanged files, nothing will happen.

4.6 Synchronizing Connection Status Between Cluster Nodes

To enable stateful packet inspection for iptables, configure and use the conntrack tools. This requires the following basic steps:

  1. Configuring the conntrackd with YaST.

  2. Configuring a resource for conntrackd (class: ocf, provider: heartbeat). If you use Hawk2 to add the resource, use the default values proposed by Hawk2.

After having configured the conntrack tools, you can use them for Linux Virtual Server, see Load Balancing.

Procedure 4.7: Configuring the conntrackd with YaST

Use the YaST cluster module to configure the user-space conntrackd. It needs a dedicated network interface that is not used for other communication channels. The daemon can be started via a resource agent afterward.

  1. Start the YaST cluster module and switch to the Configure conntrackd category.

  2. Select a Dedicated Interface for synchronizing the connection status. The IPv4 address of the selected interface is automatically detected and shown in YaST. It must already be configured and it must support multicast.

  3. Define the Multicast Address to be used for synchronizing the connection status.

  4. In Group Number, define a numeric ID for the group to synchronize the connection status to.

  5. Click Generate /etc/conntrackd/conntrackd.conf to create the configuration file for conntrackd.

  6. If you modified any options for an existing cluster, confirm your changes and close the cluster module.

  7. For further cluster configuration, click Next and proceed with Section 4.7, “Configuring Services”.

YaST Cluster—conntrackd
Figure 4.5: YaST Cluster—conntrackd

4.7 Configuring Services

In the YaST cluster module define whether to start certain services on a node at boot time. You can also use the module to start and stop the services manually. To bring the cluster nodes online and start the cluster resource manager, Pacemaker must be running as a service.

Procedure 4.8: Enabling Pacemaker
  1. In the YaST cluster module, switch to the Service category.

  2. To start Pacemaker each time this cluster node is booted, select the respective option in the Booting group. If you select Off in the Booting group, you must start Pacemaker manually each time this node is booted. To start Pacemaker manually, use the command:

    root # systemctl start pacemaker
  3. To start or stop Pacemaker immediately, click the respective button.

  4. To open the ports in the firewall that are needed for cluster communication on the current machine, activate Open Port in Firewall. The configuration is written to /etc/sysconfig/SuSEfirewall2.d/services/cluster.

  5. Confirm your changes. Note that the configuration only applies to the current machine, not to all cluster nodes.

YaST Cluster—Services
Figure 4.6: YaST Cluster—Services

4.8 Bringing the Cluster Online

After the initial cluster configuration is done, start the Pacemaker service on each cluster node to bring the stack online:

Procedure 4.9: Starting Pacemaker and Checking the Status
  1. Log in to an existing node.

  2. Check if the service is already running:

    root # systemctl status pacemaker

    If not, start Pacemaker now:

    root # systemctl start pacemaker
  3. Repeat the steps above for each of the cluster nodes.

  4. On one of the nodes, check the cluster status with the crm status command. If all nodes are online, the output should be similar to the following:

    root # crm status
    Last updated: Thu Jul  3 11:07:10 2014
    Last change: Thu Jul  3 10:58:43 2014
    Current DC: alice (175704363) - partition with quorum
    2 Nodes configured
    0 Resources configured
    
    Online: [ alice bob ]

    This output indicates that the cluster resource manager is started and is ready to manage resources.

After the basic configuration is done and the nodes are online, you can start to configure cluster resources. Use one of the cluster management tools like the crm shell (crmsh) or the HA Web Konsole. For more information, see Chapter 8, Configuring and Managing Cluster Resources (Command Line) or Chapter 7, Configuring and Managing Cluster Resources with Hawk2.

5 Upgrading Your Cluster and Updating Software Packages

Abstract

This chapter covers two different scenarios: upgrading a cluster to another version of SUSE Linux Enterprise High Availability Extension (either a major release or a service pack) as opposed to updating individual packages on cluster nodes. See Section 5.2, “Upgrading your Cluster to the Latest Product Version” versus Section 5.3, “Updating Software Packages on Cluster Nodes”.

If you want to upgrade your cluster, check Section 5.2.1, “Supported Upgrade Paths for SLE HA and SLE HA Geo” and Section 5.2.2, “Required Preparations Before Upgrading” before starting to upgrade.

5.1 Terminology

In the following, find definitions of the most important terms used in this chapter:

Major Release, General Availability (GA) Version

The Major Release of SUSE Linux Enterprise (or any software product) is a new version that brings new features and tools, decommissions previously deprecated components and comes with backward incompatible changes.

Offline Migration

If a new product version includes major changes that are backward incompatible, the cluster needs to be upgraded by an offline migration: you need to take all nodes offline and upgrade the cluster as a whole, before you can bring all nodes back online.

Rolling Upgrade

In a rolling upgrade one cluster node at a time is upgraded while the rest of the cluster is still running: you take the first node offline, upgrade it and bring it back online to join the cluster. Then you continue one by one until all cluster nodes are upgraded to a major version.

Service Pack (SP)

Combines several patches into a form that is easy to install or deploy. Service packs are numbered and usually contain security fixes, updates, upgrades, or enhancements of programs.

Update

Installation of a newer minor version of a package.

Upgrade

Installation of a newer major version of a package or distribution, which brings new features. See also Offline Migration versus Rolling Upgrade.

5.2 Upgrading your Cluster to the Latest Product Version

Which upgrade path is supported, and how to perform the upgrade depends both on the current product version and on the target version you want to migrate to.

  • Rolling upgrades are only supported from the GA of a product version to the next service pack, and from one service pack to the next.

  • Offline migrations are required to upgrade from one major version to the next major version (for example, from SLE HA 11 to SLE HA 12) or from a service pack belonging to one major version to the next major version (for example, from SLE HA 11 SP3 to SLE HA 12).

For information regarding the upgrade of the base system (SUSE Linux Enterprise Server), see the SUSE Linux Enterprise Server Deployment Guide of the target version you want to upgrade to. The guide is available at http://www.suse.com/documentation/.

Section 5.2.1 gives an overview of the supported upgrade paths for SLE HA (Geo) and the additional documentation to refer to.

Important
Important: No Support for Mixed Clusters and Reversion After Upgrade
  • Mixed clusters running on SUSE Linux Enterprise High Availability Extension 11/SUSE Linux Enterprise High Availability Extension 12 are not supported.

  • After the upgrade process to product version 12, reverting back to product version 11 is not supported.

5.2.1 Supported Upgrade Paths for SLE HA and SLE HA Geo

Upgrade From ... To

Upgrade Path

For Details See

SLE HA 11 SP3 to SLE HA (Geo) 12

Offline Migration

  • Base System: SUSE Linux Enterprise Server 12 Deployment Guide, part Updating and Upgrading SUSE Linux Enterprise

  • SLE HA: Performing a Cluster-wide Offline Migration

  • SLE HA Geo: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 Geo Clustering Quick Start, section Upgrading from SLE HA (Geo) 11 SP3 to SLE HA Geo 12

SLE HA (Geo) 11 SP4 to SLE HA (Geo) 12 SP1

Offline Migration

  • Base System: SUSE Linux Enterprise Server 12 SP1 Deployment Guide, part Updating and Upgrading SUSE Linux Enterprise

  • SLE HA: Performing a Cluster-wide Offline Migration

  • SLE HA Geo: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 SP1 Geo Clustering Quick Start, section Upgrading to the Latest Product Version

SLE HA (Geo) 12 to SLE HA (Geo) 12 SP1

Rolling Upgrade

  • Base System: SUSE Linux Enterprise Server 12 SP1 Deployment Guide, part Updating and Upgrading SUSE Linux Enterprise

  • SLE HA: Performing a Cluster-wide Rolling Upgrade

  • SLE HA Geo: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 SP1 Geo Clustering Quick Start, section Upgrading to the Latest Product Version

SLE HA (Geo) 12 SP1 to SLE HA (Geo) 12 SP2

Rolling Upgrade

  • Base System: SUSE Linux Enterprise Server 12 SP2 Deployment Guide, part Updating and Upgrading SUSE Linux Enterprise

  • SLE HA: Performing a Cluster-wide Rolling Upgrade

  • SLE HA Geo: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 SP2 Geo Clustering Quick Start, section Upgrading to the Latest Product Version

  • DRBD 8 to DRBD 9: Migrating from DRBD 8 to DRBD 9

SLE HA (Geo) 12 SP2 to SLE HA (Geo) 12 SP3

Rolling Upgrade

  • Base System: SUSE Linux Enterprise Server 12 SP3 Deployment Guide, part Updating and Upgrading SUSE Linux Enterprise

  • SLE HA: Performing a Cluster-wide Rolling Upgrade

  • SLE HA Geo: Geo Clustering for SUSE Linux Enterprise High Availability Extension 12 SP3 Geo Clustering Quick Start, section Upgrading to the Latest Product Version

All documentation listed in the column For Details See is available from http://www.suse.com/documentation/.

5.2.2 Required Preparations Before Upgrading

Backup

Ensure that your system backup is up to date and restorable.

Testing

Test the upgrade procedure on a staging instance of your cluster setup first, before performing it in a production environment.

This gives you an estimation of the time frame required for the maintenance window. It also helps to detect and solve any unexpected problems that might arise.

5.2.3 Offline Migration

This section applies to the following scenarios:

  • Upgrading from SLE HA 11 SP3 to SLE HA 12

  • Upgrading from SLE HA 11 SP4 to SLE HA 12 SP1

If your cluster is still based on an older product version than the ones listed above, first upgrade it to a version of SUSE Linux Enterprise Server and SUSE Linux Enterprise High Availability Extension that can be used as a source for upgrading to the desired target version.

The High Availability Extension 12 cluster stack comes with major changes in various components (for example, /etc/corosync/corosync.conf, disk formats of OCFS2). Therefore, a rolling upgrade from any SUSE Linux Enterprise High Availability Extension 11 version is not supported. Instead, all cluster nodes must be offline and the cluster needs to be migrated as a whole as described in Procedure 5.1, “Performing a Cluster-wide Offline Migration”.

Procedure 5.1: Performing a Cluster-wide Offline Migration
  1. Log in to each cluster node and stop the cluster stack with:

    root # rcopenais stop
  2. For each cluster node, perform an upgrade to the desired target version of SUSE Linux Enterprise Server and SUSE Linux Enterprise High Availability Extension. If you have an existing Geo cluster setup and want to upgrade it, see the additional instructions in the Geo Clustering for SUSE Linux Enterprise High Availability Extension Geo Clustering Quick Start. To find the details for the individual upgrade processes, see Section 5.2.1, “Supported Upgrade Paths for SLE HA and SLE HA Geo”.

  3. After the upgrade process has finished, reboot each node with the upgraded version of SUSE Linux Enterprise Server and SUSE Linux Enterprise High Availability Extension.

  4. If you use OCFS2 in your cluster setup, update the on-device structure by executing the following command:

    root # o2cluster --update PATH_TO_DEVICE

    It adds additional parameters to the disk which are needed for the updated OCFS2 version that is shipped with SUSE Linux Enterprise High Availability Extension 12 and 12 SPx.

  5. To update /etc/corosync/corosync.conf for Corosync version 2:

    1. Log in to one node and start the YaST cluster module.

    2. Switch to the Communication Channels category and enter values for the following new parameters: Cluster Name and Expected Votes. For details, see Procedure 4.1, “Defining the First Communication Channel (Multicast)” or Procedure 4.2, “Defining the First Communication Channel (Unicast)”, respectively.

      If YaST should detect any other options that are invalid or missing according to Corosync version 2, it will prompt you to change them.

    3. Confirm your changes in YaST. YaST will write them to /etc/corosync/corosync.conf.

    4. If Csync2 is configured for your cluster, use the following command to push the updated Corosync configuration to the other cluster nodes:

      root # csync2 -xv

      For details on Csync2, see Section 4.5, “Transferring the Configuration to All Nodes”.

      Alternatively, synchronize the updated Corosync configuration by manually copying /etc/corosync/corosync.conf to all cluster nodes.

  6. Log in to each node and start the cluster stack with:

    root # systemctl start pacemaker
  7. Check the cluster status with crm status or with Hawk2.

  8. Configure the following services to start at boot time:

    root # systemctl enable pacemaker
    root # systemctl enable hawk
    root # systemctl enable sbd
Note
Note: Upgrading the CIB Syntax Version

Tags (for grouping resources) and some ACL features only work with the CIB syntax version pacemaker-2.0 or higher. (To check your version, use the cibadmin -Q |grep validate-with command.) If you have upgraded from SUSE Linux Enterprise High Availability Extension 11 SPx, your CIB version will not be upgraded by default. To manually upgrade to the latest CIB version use one of the following commands:

root # cibadmin --upgrade --force

or

root # crm configure upgrade force

5.2.4 Rolling Upgrade

This section applies to the following scenarios:

  • Upgrading from SLE HA 12 to SLE HA 12 SP1

  • Upgrading from SLE HA 12 SP1 to SLE HA 12 SP2

  • Upgrading from SLE HA (Geo) 12 SP2 to SLE HA (Geo) 12 SP3

Warning
Warning: Active Cluster Stack

Before starting an upgrade for a node, stop the cluster stack on that node.

If the cluster resource manager on a node is active during the software update, this can lead to unpredictable results like fencing of active nodes.

Procedure 5.2: Performing a Cluster-wide Rolling Upgrade
  1. Log in as root on the node that you want to upgrade and stop the cluster stack:

    root # systemctl stop pacemaker
  2. Perform an upgrade to the desired target version of SUSE Linux Enterprise Server and SUSE Linux Enterprise High Availability Extension. To find the details for the individual upgrade processes, see Section 5.2.1, “Supported Upgrade Paths for SLE HA and SLE HA Geo”.

  3. Restart the cluster stack on the upgraded node to make the node rejoin the cluster:

    root # systemctl start pacemaker
  4. Take the next node offline and repeat the procedure for that node.

  5. Check the cluster status with crm status or with Hawk2.

Important
Important: Time Limit for Rolling Upgrade

The new features shipped with the latest product version will only be available after all cluster nodes have been upgraded to the latest product version. Mixed version clusters are only supported for a short time frame during the rolling upgrade. Complete the rolling upgrade within one week.

The Hawk2 Status screen also shows a warning if different CRM versions are detected for your cluster nodes.

5.3 Updating Software Packages on Cluster Nodes

Warning
Warning: Active Cluster Stack

Before starting an update for a node, either stop the cluster stack on that node or put the node into maintenance mode, depending on whether the cluster stack is affected or not. See Step 1 for details.

If the cluster resource manager on a node is active during the software update, this can lead to unpredictable results like fencing of active nodes.

  1. Before installing any package updates on a node, check the following:

    • Does the update affect any packages belonging to SUSE Linux Enterprise High Availability Extension or the Geo clustering extension? If yes: Stop the cluster stack on the node before starting the software update:

      root # systemctl stop pacemaker
    • Does the package update require a reboot? If yes: Stop the cluster stack on the node before starting the software update:

      root # systemctl stop pacemaker
    • If none of the situations above apply, you do not need to stop the cluster stack. In that case, put the node into maintenance mode before starting the software update:

      root # crm node maintenance NODE_NAME

      For more details on maintenance mode, see Section 16.2, “Different Options for Maintenance Tasks”.

  2. Install the package update using either YaST or Zypper.

  3. After the update has been successfully installed:

    • Either start the cluster stack on the respective node (if you stopped it in Step 1):

      root # systemctl start pacemaker
    • or remove the maintenance flag to bring the node back to normal mode:

      root # crm node ready NODE_NAME
  4. Check the cluster status with crm status or with Hawk2.

5.4 For More Information

For detailed information about any changes and new features of the product you are upgrading to, refer to its release notes. They are available from https://www.suse.com/releasenotes/.

Part II Configuration and Administration

6 Configuration and Administration Basics

The main purpose of an HA cluster is to manage user services. Typical examples of user services are an Apache Web server or a database. From the user's point of view, the services do something specific when ordered to do so. To the cluster, however, they are only resources which may be started or stopped—the nature of the service is irrelevant to the cluster.

In this chapter, we will introduce some basic concepts you need to know when configuring resources and administering your cluster. The following chapters show you how to execute the main configuration and administration tasks with each of the management tools the High Availability Extension provides.

7 Configuring and Managing Cluster Resources with Hawk2

To configure and manage cluster resources, either use HA Web Konsole (Hawk2), or the crm shell (crmsh) command line utility. If you upgrade from an earlier version of SUSE® Linux Enterprise High Availability Extension where Hawk was installed, the package will be replaced with the current version, Hawk2.

Hawk2's Web-based user-interface allows you to monitor and administer your Linux cluster from non-Linux machines. Furthermore, it is the ideal solution in case your system only provides a minimal graphical user interface.

8 Configuring and Managing Cluster Resources (Command Line)

To configure and manage cluster resources, either use the crm shell (crmsh) command line utility or HA Web Konsole (Hawk2), a Web-based user interface.

This chapter introduces crm, the command line tool and covers an overview of this tool, how to use templates, and mainly configuring and managing cluster resources: creating basic and advanced types of resources (groups and clones), configuring constraints, specifying failover nodes and failback nodes, configuring resource monitoring, starting, cleaning up or removing resources, and migrating resources manually.

9 Adding or Modifying Resource Agents

All tasks that need to be managed by a cluster must be available as a resource. There are two major groups here to consider: resource agents and STONITH agents. For both categories, you can add your own agents, extending the abilities of the cluster to your own needs.

10 Fencing and STONITH

Fencing is a very important concept in computer clusters for HA (High Availability). A cluster sometimes detects that one of the nodes is behaving strangely and needs to remove it. This is called fencing and is commonly done with a STONITH resource. Fencing may be defined as a method to bring an HA cluster to a known state.

Every resource in a cluster has a state attached. For example: resource r1 is started on alice. In an HA cluster, such a state implies that resource r1 is stopped on all nodes except alice, because the cluster must make sure that every resource may be started on only one node. Every node must report every change that happens to a resource. The cluster state is thus a collection of resource states and node states.

When the state of a node or resource cannot be established with certainty, fencing comes in. Even when the cluster is not aware of what is happening on a given node, fencing can ensure that the node does not run any important resources.

11 Storage Protection and SBD

SBD (STONITH Block Device) provides a node fencing mechanism for Pacemaker-based clusters through the exchange of messages via shared block storage (SAN, iSCSI, FCoE, etc.). This isolates the fencing mechanism from changes in firmware version or dependencies on specific firmware controllers. SBD needs a watchdog on each node to ensure that misbehaving nodes are really stopped. Under certain conditions, it is also possible to use SBD without shared storage, by running it in diskless mode.

The ha-cluster-bootstrap scripts provide an automated way to set up a cluster with the option of using SBD as fencing mechanism. For details, see the Installation and Setup Quick Start. However, manually setting up SBD provides you with more options regarding the individual settings.

This chapter explains the concepts behind SBD. It guides you through configuring the components needed by SBD to protect your cluster from potential data corruption in case of a split brain scenario.

In addition to node level fencing, you can use additional mechanisms for storage protection, such as LVM2 exclusive activation or OCFS2 file locking support (resource level fencing). They protect your system against administrative or application faults.

12 Access Control Lists

The cluster administration tools like crm shell (crmsh) or Hawk2 can be used by root or any user in the group haclient. By default, these users have full read/write access. To limit access or assign more fine-grained access rights, you can use Access control lists (ACLs).

Access control lists consist of an ordered set of access rules. Each rule allows read or write access or denies access to a part of the cluster configuration. Rules are typically combined to produce a specific role, then users may be assigned to a role that matches their tasks.

13 Network Device Bonding

For many systems, it is desirable to implement network connections that comply to more than the standard data security or availability requirements of a typical Ethernet device. In these cases, several Ethernet devices can be aggregated to a single bonding device.

14 Load Balancing

Load Balancing makes a cluster of servers appear as one large, fast server to outside clients. This apparent single server is called a virtual server. It consists of one or more load balancers dispatching incoming requests and several real servers running the actual services. With a load balancing setup of High Availability Extension, you can build highly scalable and highly available network services, such as Web, cache, mail, FTP, media and VoIP services.

15 Geo Clusters (Multi-Site Clusters)

Apart from local clusters and metro area clusters, SUSE® Linux Enterprise High Availability Extension 12 SP3 also supports geographically dispersed clusters (Geo clusters, sometimes also called multi-site clusters). That means you can have multiple, geographically dispersed sites with a local cluster each. Failover between these clusters is coordinated by a higher level entity, the so-called booth. Support for Geo clusters is available as a separate extension to Geo Clustering for SUSE Linux Enterprise High Availability Extension. For details on how to use and set up Geo clusters, refer to the Geo Clustering Quick Start or the Geo Clustering Guide. Both are available from http://www.suse.com/documentation/sle-ha-geo-12.

16 Executing Maintenance Tasks

To perform maintenance tasks on the cluster nodes, you might need to stop the resources running on that node, to move them, or to shut down or reboot the node. It might also be necessary to temporarily take over the control of resources from the cluster, or even to stop the cluster service while resources remain running.

This chapter explains how to manually take down a cluster node without negative side-effects. It also gives an overview of different options the cluster stack provides for executing maintenance tasks.

6 Configuration and Administration Basics

Abstract

The main purpose of an HA cluster is to manage user services. Typical examples of user services are an Apache Web server or a database. From the user's point of view, the services do something specific when ordered to do so. To the cluster, however, they are only resources which may be started or stopped—the nature of the service is irrelevant to the cluster.

In this chapter, we will introduce some basic concepts you need to know when configuring resources and administering your cluster. The following chapters show you how to execute the main configuration and administration tasks with each of the management tools the High Availability Extension provides.

6.1 Use Case Scenarios

In general, clusters fall into one of two categories:

  • Two-node clusters

  • clusters with more than two nodes. This means usually an odd number of nodes.

Adding also different topologies, different use cases can be derived. The following use cases are the most common:

Two-node cluster in one location

Configuration: FC SAN or similar shared storage, layer 2 network.

Usage scenario: Embedded clusters that focus on service high availability and not data redundancy for data replication. Such a setup is used for radio stations or assembly line controllers, for example.

Two-node clusters in two locations (most widely used)

Configuration: Symmetrical stretched cluster, FC SAN, and layer 2 network all across two locations.

Usage scenario: Classical stretched clusters, focus on service high availability and local data redundancy. For databases and enterprise resource planning. One of the most popular setup during the last years.

Odd number of nodes in three locations

Configuration: 2×N+1 nodes, FC SAN across two main locations. Auxiliary third site with no FC SAN, but acts as a majority maker. Layer 2 network at least across two main locations.

Usage scenario: Classical stretched cluster, focus on service high availability and data redudancy. For example, databases, enterprise resource planning.

6.2 Quorum Determination

Whenever communication fails between one or more nodes and the rest of the cluster, a cluster partition occurs. The nodes can only communicate with other nodes in the same partition and are unaware of the separated nodes. A cluster partition is defined to have quorum (is quorate) if it has the majority of nodes (or votes). How this is achieved is done by quorum calculation. Quorum is a requirement for fencing.

Quorum calculation has changed between SUSE Linux Enterprise High Availability Extension 11 and SUSE Linux Enterprise High Availability Extension 15. For SUSE Linux Enterprise High Availability Extension 11, quorum was calculated by Pacemaker. Starting with SUSE Linux Enterprise High Availability Extension 12, Corosync can handle quorum for two-node clusters directly without changing the Pacemaker configuration.

How quorum is calculated is influenced by the following factors:

Number of Cluster Nodes

To keep services running, a cluster with more than two nodes relies on quorum (majority vote) to resolve cluster partitions. Based on the following formula, you can calculate the minimum number of operational nodes required for the cluster to function:

N ≥ C/2 + 1

N = minimum number of operational nodes
C = number of cluster nodes

For example, a five-node cluster needs a minimum of three operational nodes (or two nodes which can fail).

We strongly recommend to use either a two-node cluster or an odd number of cluster nodes. Two-node clusters make sense for stretched setups across two sites. Clusters with an odd number of nodes can be built on either one single site or might be spread across three sites.

Corosync Configuration

Corosync is a messaging and membership layer, see Section 6.2.4, “Corosync Configuration for Two-Node Clusters” and Section 6.2.5, “Corosync Configuration for N-Node Clusters”.

6.2.1 Global Cluster Options

Global cluster options control how the cluster behaves when confronted with certain situations. They are grouped into sets and can be viewed and modified with the cluster management tools like Hawk2 and the crm shell.

The predefined values can usually be kept. However, to make key functions of your cluster work correctly, you need to adjust the following parameters after basic cluster setup:

6.2.2 Global Option no-quorum-policy

This global option defines what to do when a cluster partition does not have quorum (no majority of nodes is part of the partition).

Allowed values are:

ignore

Setting no-quorum-policy to ignore makes the cluster behave like it has quorum. Resource management is continued.

This was the default for SLES 11 for a two-node cluster. Starting with SLES 12, this option is obsolete. Based on configuration and conditions, Corosync gives cluster nodes or a single node quorum—or not.

For two node clusters the only meaningful behaviour is to always react in case of quorum loss. The first step always should be trying to fence the lost node.

freeze

If quorum is lost, the cluster partition freezes. Resource management is continued: running resources are not stopped (but possibly restarted in response to monitor events), but no further resources are started within the affected partition.

This setting is recommended for clusters where certain resources depend on communication with other nodes (for example, OCFS2 mounts). In this case, the default setting no-quorum-policy=stop is not useful, as it would lead to the following scenario: Stopping those resources would not be possible while the peer nodes are unreachable. Instead, an attempt to stop them would eventually time out and cause a stop failure, triggering escalated recovery and fencing.

stop (default value)

If quorum is lost, all resources in the affected cluster partition are stopped in an orderly fashion.

suicide

If quorum is lost, all nodes in the affected cluster partition are fenced. This option works only in combination with SBD, see Chapter 11, Storage Protection and SBD.

6.2.3 Global Option stonith-enabled

This global option defines whether to apply fencing, allowing STONITH devices to shoot failed nodes and nodes with resources that cannot be stopped. By default, this global option is set to true, because for normal cluster operation it is necessary to use STONITH devices. According to the default value, the cluster will refuse to start any resources if no STONITH resources have been defined.

If you need to disable fencing for any reasons, set stonith-enabled to false, but be aware that this has impact on the support status for your product. Furthermore, with stonith-enabled="false", resources like the Distributed Lock Manager (DLM) and all services depending on DLM (such as cLVM, GFS2, and OCFS2) will fail to start.

Important
Important: No Support Without STONITH

A cluster without STONITH is not supported.

6.2.4 Corosync Configuration for Two-Node Clusters

When using the bootstrap scripts, the Corosync configuration contains a quorum section with the following options:

Example 6.1: Excerpt of Corosync Configuration for a Two-Node Cluster
quorum {
   # Enable and configure quorum subsystem (default: off)
   # see also corosync.conf.5 and votequorum.5
   provider: corosync_votequorum
   expected_votes: 2
   two_node: 1
}

As opposed to SUSE Linux Enterprise 11, the votequorum subsystem in SUSE Linux Enterprise 12 is powered by Corosync version 2.x. This means that the no-quorum-policy=ignore option must not be used.

By default, when two_node: 1 is set, the wait_for_all option is automatically enabled. If wait_for_all is not enbaled, the cluster should be started on both nodes in parallel. Otherwise the first node will perform a startup-fencing on the missing second node.

6.2.5 Corosync Configuration for N-Node Clusters

When not using a two-node cluster, we strongly recommend an odd number of nodes for your N-node cluster. With regards to quorum configuration, you have the following options:

  • Adding additional nodes with the ha-cluster-join command, or

  • Adapting the Corosync configuration manually.

If you adjust /etc/corosync/corosync.conf manually, use the following settings:

Example 6.2: Excerpt of Corosync Configuration for a N-Node Cluster
quorum {
   provider: corosync_votequorum 1
   expected_votes: N 2
   wait_for_all: 1 3
}

1

Use the quorum service from Corosync

2

The number of votes to expect. This parameter can either be provided inside the quorum section, or is automatically calculated when the nodelist section is available.

3

Enables the wait for all (WFA) feature. When WFA is enabled, the cluster will be quorate for the first time only after all nodes have been visible. To avoid some startup race conditions, setting wait_for_all to 1 may help. For example, in a five-node cluster every node has one vote and thus, expected_votes is set to 5. As soon as three or more nodes are visible to each other, the cluster partition becomes quorate and can start operating.

6.3 Cluster Resources

As a cluster administrator, you need to create cluster resources for every resource or application you run on servers in your cluster. Cluster resources can include Web sites, e-mail servers, databases, file systems, virtual machines, and any other server-based applications or services you want to make available to users at all times.

6.3.1 Resource Management

Before you can use a resource in the cluster, it must be set up. For example, if you want to use an Apache server as a cluster resource, set up the Apache server first and complete the Apache configuration before starting the respective resource in your cluster.

If a resource has specific environment requirements, make sure they are present and identical on all cluster nodes. This kind of configuration is not managed by the High Availability Extension. You must do this yourself.

Note
Note: Do Not Touch Services Managed by the Cluster

When managing a resource with the High Availability Extension, the same resource must not be started or stopped otherwise (outside of the cluster, for example manually or on boot or reboot). The High Availability Extension software is responsible for all service start or stop actions.

If you need to execute testing or maintenance tasks after the services are already running under cluster control, make sure to put the resources, nodes, or the whole cluster into maintenance mode before you touch any of them manually. For details, see Section 16.2, “Different Options for Maintenance Tasks”.

After having configured the resources in the cluster, use the cluster management tools to start, stop, clean up, remove or migrate any resources manually. For details how to do so with your preferred cluster management tool:

6.3.2 Supported Resource Agent Classes

For each cluster resource you add, you need to define the standard that the resource agent conforms to. Resource agents abstract the services they provide and present an accurate status to the cluster, which allows the cluster to be non-committal about the resources it manages. The cluster relies on the resource agent to react appropriately when given a start, stop or monitor command.

Typically, resource agents come in the form of shell scripts. The High Availability Extension supports the following classes of resource agents:

Open Cluster Framework (OCF) Resource Agents

OCF RA agents are best suited for use with High Availability, especially when you need multi-state resources or special monitoring abilities. The agents are generally located in /usr/lib/ocf/resource.d/provider/. Their functionality is similar to that of LSB scripts. However, the configuration is always done with environmental variables which allow them to accept and process parameters easily. The OCF specification (as it relates to resource agents) can be found at http://www.opencf.org/cgi-bin/viewcvs.cgi/specs/ra/resource-agent-api.txt?rev=HEAD&content-type=text/vnd.viewcvs-markup. OCF specifications have strict definitions of which exit codes must be returned by actions, see Section 9.3, “OCF Return Codes and Failure Recovery”. The cluster follows these specifications exactly.

All OCF Resource Agents are required to have at least the actions start, stop, status, monitor, and meta-data. The meta-data action retrieves information about how to configure the agent. For example, if you want to know more about the IPaddr agent by the provider heartbeat, use the following command:

OCF_ROOT=/usr/lib/ocf /usr/lib/ocf/resource.d/heartbeat/IPaddr meta-data

The output is information in XML format, including several sections (general description, available parameters, available actions for the agent).

Alternatively, use the crmsh to view information on OCF resource agents. For details, see Section 8.1.3, “Displaying Information about OCF Resource Agents”.

Linux Standards Base (LSB) Scripts

LSB resource agents are generally provided by the operating system/distribution and are found in /etc/init.d. To be used with the cluster, they must conform to the LSB init script specification. For example, they must have several actions implemented, which are, at minimum, start, stop, restart, reload, force-reload, and status. For more information, see http://refspecs.linuxbase.org/LSB_4.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html.

The configuration of those services is not standardized. If you intend to use an LSB script with High Availability, make sure that you understand how the relevant script is configured. Often you can find information about this in the documentation of the relevant package in /usr/share/doc/packages/PACKAGENAME.

Systemd

Starting with SUSE Linux Enterprise 12, systemd is a replacement for the popular System V init daemon. Pacemaker can manage systemd services if they are present. Instead of init scripts, systemd has unit files. Generally the services (or unit files) are provided by the operating system. In case you want to convert existing init scripts, find more information at http://0pointer.de/blog/projects/systemd-for-admins-3.html.

Service

There are currently many common types of system services that exist in parallel: LSB (belonging to System V init), systemd, and (in some distributions) upstart. Therefore, Pacemaker supports a special alias which intelligently figures out which one applies to a given cluster node. This is particularly useful when the cluster contains a mix of systemd, upstart, and LSB services. Pacemaker will try to find the named service in the following order: as an LSB (SYS-V) init script, a Systemd unit file, or an Upstart job.

Nagios

Monitoring plug-ins (formerly called Nagios plug-ins) allow to monitor services on remote hosts. Pacemaker can do remote monitoring with the monitoring plug-ins if they are present. For detailed information, see Section 6.6.1, “Monitoring Services on Remote Hosts with Monitoring Plug-ins”.

STONITH (Fencing) Resource Agents

This class is used exclusively for fencing related resources. For more information, see Chapter 10, Fencing and STONITH.

The agents supplied with the High Availability Extension are written to OCF specifications.

6.3.3 Types of Resources

The following types of resources can be created:

Primitives

A primitive resource, the most basic type of resource.

Learn how to create primitive resources with your preferred cluster management tool:

Groups

Groups contain a set of resources that need to be located together, started sequentially and stopped in the reverse order. For more information, refer to Section 6.3.5.1, “Groups”.

Clones

Clones are resources that can be active on multiple hosts. Any resource can be cloned, provided the respective resource agent supports it. For more information, refer to Section 6.3.5.2, “Clones”.

Multi-state Resources (formerly known as Master/Slave Resources)

Multi-state resources are a special type of clone resources that can have multiple modes. For more information, refer to Section 6.3.5.3, “Multi-state Resources”.

6.3.4 Resource Templates

If you want to create lots of resources with similar configurations, defining a resource template is the easiest way. After having been defined, it can be referenced in primitives—or in certain types of constraints, as described in Section 6.5.3, “Resource Templates and Constraints”.

If a template is referenced in a primitive, the primitive will inherit all operations, instance attributes (parameters), meta attributes, and utilization attributes defined in the template. Additionally, you can define specific operations or attributes for your primitive. If any of these are defined in both the template and the primitive, the values defined in the primitive will take precedence over the ones defined in the template.

Learn how to define resource templates with your preferred cluster configuration tool:

6.3.5 Advanced Resource Types

Whereas primitives are the simplest kind of resources and therefore easy to configure, you will probably also need more advanced resource types for cluster configuration, such as groups, clones or multi-state resources.

6.3.5.1 Groups

Some cluster resources depend on other components or resources. They require that each component or resource starts in a specific order and runs together on the same server with resources it depends on. To simplify this configuration, you can use cluster resource groups.

Example 6.3: Resource Group for a Web Server

An example of a resource group would be a Web server that requires an IP address and a file system. In this case, each component is a separate resource that is combined into a cluster resource group. The resource group would run on one or more servers. In case of a software or hardware malfunction, the group would fail over to another server in the cluster, similar to an individual cluster resource.

Group Resource
Figure 6.1: Group Resource

Groups have the following properties:

Starting and Stopping

Resources are started in the order they appear in and stopped in the reverse order.

Dependency

If a resource in the group cannot run anywhere, then none of the resources located after that resource in the group is allowed to run.

Contents

Groups may only contain a collection of primitive cluster resources. Groups must contain at least one resource, otherwise the configuration is not valid. To refer to the child of a group resource, use the child’s ID instead of the group’s ID.

Constraints

Although it is possible to reference the group’s children in constraints, it is usually preferable to use the group’s name instead.

Stickiness

Stickiness is additive in groups. Every active member of the group will contribute its stickiness value to the group’s total. So if the default resource-stickiness is 100 and a group has seven members (five of which are active), the group as a whole will prefer its current location with a score of 500.

Resource Monitoring

To enable resource monitoring for a group, you must configure monitoring separately for each resource in the group that you want monitored.

Learn how to create groups with your preferred cluster management tool:

6.3.5.2 Clones

You may want certain resources to run simultaneously on multiple nodes in your cluster. To do this you must configure a resource as a clone. Examples of resources that might be configured as clones include cluster file systems like OCFS2. You can clone any resource provided. This is supported by the resource’s Resource Agent. Clone resources may even be configured differently depending on which nodes they are hosted.

There are three types of resource clones:

Anonymous Clones

These are the simplest type of clones. They behave identically anywhere they are running. Because of this, there can only be one instance of an anonymous clone active per machine.

Globally Unique Clones

These resources are distinct entities. An instance of the clone running on one node is not equivalent to another instance on another node; nor would any two instances on the same node be equivalent.

Stateful Clones (Multi-state Resources)

Active instances of these resources are divided into two states, active and passive. These are also sometimes called primary and secondary, or master and slave. Stateful clones can be either anonymous or globally unique. See also Section 6.3.5.3, “Multi-state Resources”.

Clones must contain exactly one group or one regular resource.

When configuring resource monitoring or constraints, clones have different requirements than simple resources. For details, see Pacemaker Explained, available from http://www.clusterlabs.org/doc/. Refer to section Clones - Resources That Get Active on Multiple Hosts.

Learn how to create clones with your preferred cluster management tool:

6.3.5.3 Multi-state Resources

Multi-state resources are a specialization of clones. They allow the instances to be in one of two operating modes (called master or slave, but can mean whatever you want them to mean). Multi-state resources must contain exactly one group or one regular resource.

When configuring resource monitoring or constraints, multi-state resources have different requirements than simple resources. For details, see Pacemaker Explained, available from http://www.clusterlabs.org/doc/. Refer to section Multi-state - Resources That Have Multiple Modes.

6.3.6 Resource Options (Meta Attributes)

For each resource you add, you can define options. Options are used by the cluster to decide how your resource should behave—they tell the CRM how to treat a specific resource. Resource options can be set with the crm_resource --meta command or with Hawk2 as described in Procedure 7.5, “Adding a Primitive Resource”.

Table 6.1: Options for a Primitive Resource

Option

Description

Default

priority

If not all resources can be active, the cluster will stop lower priority resources to keep higher priority ones active.

0

target-role

In what state should the cluster attempt to keep this resource? Allowed values: stopped, started, master.

started

is-managed

Is the cluster allowed to start and stop the resource? Allowed values: true, false. If the value is set to false, the status of the resource is still monitored and any failures are reported (which is different from setting a resource to maintenance="true").

true

maintenance

Can the resources be touched manually? Allowed values: true, false. If set to true, all resources become unmanaged: the cluster will stop monitoring them and thus be oblivious about their status. You can stop or restart cluster resources at will, without the cluster attempting to restart them.

false

resource-stickiness

How much does the resource prefer to stay where it is?

calculated

migration-threshold

How many failures should occur for this resource on a node before making the node ineligible to host this resource?

INFINITY (disabled)

multiple-active

What should the cluster do if it ever finds the resource active on more than one node? Allowed values: block (mark the resource as unmanaged), stop_only, stop_start.

stop_start

failure-timeout

How many seconds to wait before acting as if the failure had not occurred (and potentially allowing the resource back to the node on which it failed)?

0 (disabled)

allow-migrate

Allow resource migration for resources which support migrate_to/migrate_from actions.

false

remote-node

The name of the remote node this resource defines. This both enables the resource as a remote node and defines the unique name used to identify the remote node. If no other parameters are set, this value will also be assumed as the host name to connect to at remote-portport.

Warning
Warning: Use Unique IDs

This value must not overlap with any existing resource or node IDs.

none (disabled)

remote-port

Custom port for the guest connection to pacemaker_remote.

3121

remote-addr

The IP address or host name to connect to if the remote node’s name is not the host name of the guest.

remote-node (value used as host name)

remote-connect-timeout

How long before a pending guest connection will time out.

60s

6.3.7 Instance Attributes (Parameters)

The scripts of all resource classes can be given parameters which determine how they behave and which instance of a service they control. If your resource agent supports parameters, you can add them with the crm_resource command or with Hawk2 as described in Procedure 7.5, “Adding a Primitive Resource”. In the crm command line utility and in Hawk2, instance attributes are called params or Parameter, respectively. The list of instance attributes supported by an OCF script can be found by executing the following command as root:

root # crm ra info [class:[provider:]]resource_agent

or (without the optional parts):

root # crm ra info resource_agent

The output lists all the supported attributes, their purpose and default values.

For example, the command

root # crm ra info IPaddr

returns the following output:

Manages virtual IPv4 addresses (portable version) (ocf:heartbeat:IPaddr)
    
This script manages IP alias IP addresses
It can add an IP alias, or remove one.   
    
Parameters (* denotes required, [] the default):
    
ip* (string): IPv4 address
The IPv4 address to be configured in dotted quad notation, for example
"192.168.1.1".                                                        
    
nic (string, [eth0]): Network interface
The base network interface on which the IP address will be brought
online.                                                           
    
If left empty, the script will try and determine this from the    
routing table.                                                    
    
Do NOT specify an alias interface in the form eth0:1 or anything here;
rather, specify the base interface only.                              
    
cidr_netmask (string): Netmask
The netmask for the interface in CIDR format. (ie, 24), or in
dotted quad notation  255.255.255.0).                        
    
If unspecified, the script will also try to determine this from the
routing table.                                                     
    
broadcast (string): Broadcast address
Broadcast address associated with the IP. If left empty, the script will
determine this from the netmask.                                        
    
iflabel (string): Interface label
You can specify an additional label for your IP address here.
    
lvs_support (boolean, [false]): Enable support for LVS DR
Enable support for LVS Direct Routing configurations. In case a IP
address is stopped, only move it to the loopback device to allow the
local node to continue to service requests, but no longer advertise it
on the network.                                                       
    
local_stop_script (string): 
Script called when the IP is released
    
local_start_script (string): 
Script called when the IP is added
    
ARP_INTERVAL_MS (integer, [500]): milliseconds between gratuitous ARPs
milliseconds between ARPs                                         
    
ARP_REPEAT (integer, [10]): repeat count
How many gratuitous ARPs to send out when bringing up a new address
    
ARP_BACKGROUND (boolean, [yes]): run in background
run in background (no longer any reason to do this)
    
ARP_NETMASK (string, [ffffffffffff]): netmask for ARP
netmask for ARP - in nonstandard hexadecimal format.
    
Operations' defaults (advisory minimum):
    
start         timeout=90
stop          timeout=100
monitor_0     interval=5s timeout=20s
Note
Note: Instance Attributes for Groups, Clones or Multi-state Resources

Note that groups, clones and multi-state resources do not have instance attributes. However, any instance attributes set will be inherited by the group's, clone's or multi-state resource's children.

6.3.8 Resource Operations

By default, the cluster will not ensure that your resources are still healthy. To instruct the cluster to do this, you need to add a monitor operation to the resource’s definition. Monitor operations can be added for all classes or resource agents. For more information, refer to Section 6.4, “Resource Monitoring”.

Table 6.2: Resource Operation Properties

Operation

Description

id

Your name for the action. Must be unique. (The ID is not shown).

name

The action to perform. Common values: monitor, start, stop.

interval

How frequently to perform the operation. Unit: seconds

timeout

How long to wait before declaring the action has failed.

requires

What conditions need to be satisfied before this action occurs. Allowed values: nothing, quorum, fencing. The default depends on whether fencing is enabled and if the resource’s class is stonith. For STONITH resources, the default is nothing.

on-fail

The action to take if this action ever fails. Allowed values:

  • ignore: Pretend the resource did not fail.

  • block: Do not perform any further operations on the resource.

  • stop: Stop the resource and do not start it elsewhere.

  • restart: Stop the resource and start it again (possibly on a different node).

  • fence: Bring down the node on which the resource failed (STONITH).

  • standby: Move all resources away from the node on which the resource failed.

enabled

If false, the operation is treated as if it does not exist. Allowed values: true, false.

role

Run the operation only if the resource has this role.

record-pending

Can be set either globally or for individual resources. Makes the CIB reflect the state of in-flight operations on resources.

description

Description of the operation.

6.3.9 Timeout Values

Timeouts values for resources can be influenced by the following parameters:

  • op_defaults (global timeout for operations),

  • a specific timeout value defined in a resource template,

  • a specific timeout value defined for a resource.

Note
Note: Priority of Values

If a specific value is defined for a resource, it takes precedence over the global default. A specific value for a resource also takes precedence over a value that is defined in a resource template.

Getting timeout values right is very important. Setting them too low will result in a lot of (unnecessary) fencing operations for the following reasons:

  1. If a resource runs into a timeout, it fails and the cluster will try to stop it.

  2. If stopping the resource also fails (for example, because the timeout for stopping is set too low), the cluster will fence the node. It considers the node where this happens to be out of control.

You can adjust the global default for operations and set any specific timeout values with both crmsh and Hawk2. The best practice for determining and setting timeout values is as follows:

Procedure 6.1: Determining Timeout Values
  1. Check how long it takes your resources to start and stop (under load).

  2. If needed, add the op_defaults parameter and set the (default) timeout value accordingly:

    1. For example, set op_defaults to 60 seconds:

      crm(live)configure#  op_defaults timeout=60
    2. For resources that need longer periods of time, define individual timeout values.

  3. When configuring operations for a resource, add separate start and stop operations. When configuring operations with Hawk2, it will provide useful timeout proposals for those operations.

6.4 Resource Monitoring

If you want to ensure that a resource is running, you must configure resource monitoring for it.

If the resource monitor detects a failure, the following takes place:

  • Log file messages are generated, according to the configuration specified in the logging section of /etc/corosync/corosync.conf.

  • The failure is reflected in the cluster management tools (Hawk2, crm status), and in the CIB status section.

  • The cluster initiates noticeable recovery actions which may include stopping the resource to repair the failed state and restarting the resource locally or on another node. The resource also may not be restarted, depending on the configuration and state of the cluster.

If you do not configure resource monitoring, resource failures after a successful start will not be communicated, and the cluster will always show the resource as healthy.

Monitoring Stopped Resources

Usually, resources are only monitored by the cluster as long as they are running. However, to detect concurrency violations, also configure monitoring for resources which are stopped. For example:

primitive dummy1 ocf:heartbeat:Dummy \
    op monitor interval="300s" role="Stopped" timeout="10s" \
    op monitor interval="30s" timeout="10s"

This configuration triggers a monitoring operation every 300 seconds for the resource dummy1 as soon as it is in role="Stopped". When running, it will be monitored every 30 seconds.

Probing

The CRM executes an initial monitoring for each resource on every node, the so-called probe. A probe is also executed after the cleanup of a resource. If multiple monitoring operations are defined for a resource, the CRM will select the one with the smallest interval and will use its timeout value as default timeout for probing. If no monitor operation is configured, the cluster-wide default applies. The default is 20 seconds (if not specified otherwise by configuring the op_defaults parameter). If you do not want to rely on the automatic calculation or the op_defaults value, define a specific monitoring operation for the probing of this resource. Do so by adding a monitoring operation with the interval set to 0, for example:

crm(live)configure# primitive rsc1 ocf:pacemaker:Dummy \
    op monitor interval="0" timeout="60"

The probe of rsc1 will time out in 60s, independent of the global timeout defined in op_defaults, or any other operation timeouts configured. If you did not set interval="0" for specifying the probing of the respective resource, the CRM will automatically check for any other monitoring operations defined for that resource and will calculate the timeout value for probing as described above.

Learn how to add monitor operations to resources with your preferred cluster management tool:

6.5 Resource Constraints

Having all the resources configured is only part of the job. Even if the cluster knows all needed resources, it might still not be able to handle them correctly. Resource constraints let you specify which cluster nodes resources can run on, what order resources will load, and what other resources a specific resource is dependent on.

6.5.1 Types of Constraints

There are three different kinds of constraints available:

Resource Location

Locational constraints that define on which nodes a resource may be run, may not be run or is preferred to be run.

Resource Colocation

Colocational constraints that tell the cluster which resources may or may not run together on a node.

Resource Order

Ordering constraints to define the sequence of actions.

Important
Important: Restrictions for Constraints and Certain Types of Resources
  • Do not create colocation constraints for members of a resource group. Create a colocation constraint pointing to the resource group as a whole instead. All other types of constraints are safe to use for members of a resource group.

  • Do not use any constraints on a resource that has a clone resource or a multi-state resource applied to it. The constraints must apply to the clone or multi-state resource, not to the child resource.

6.5.1.1 Resource Sets

6.5.1.1.1 Using Resource Sets for Defining Constraints

As an alternative format for defining location, colocation or ordering constraints, you can use resource sets, where primitives are grouped together in one set. Previously this was possible either by defining a resource group (which could not always accurately express the design), or by defining each relationship as an individual constraint. The latter caused a constraint explosion as the number of resources and combinations grew. The configuration via resource sets is not necessarily less verbose, but is easier to understand and maintain, as the following examples show.

Example 6.4: A Resource Set for Location Constraints

For example, you can use the following configuration of a resource set (loc-alice) in the crmsh to place two virtual IPs (vip1 and vip2) on the same node, alice:

crm(live)configure# primitive vip1 ocf:heartbeat:IPaddr2 params ip=192.168.1.5
crm(live)configure# primitive vip1 ocf:heartbeat:IPaddr2 params ip=192.168.1.6
crm(live)configure# location loc-alice { vip1 vip2 } inf: alice

If you want to use resource sets to replace a configuration of colocation constraints, consider the following two examples:

Example 6.5: A Chain of Colocated Resources
<constraints>
     <rsc_colocation id="coloc-1" rsc="B" with-rsc="A" score="INFINITY"/>
     <rsc_colocation id="coloc-2" rsc="C" with-rsc="B" score="INFINITY"/>
     <rsc_colocation id="coloc-3" rsc="D" with-rsc="C" score="INFINITY"/>
</constraints>

The same configuration expressed by a resource set:

<constraints>
    <rsc_colocation id="coloc-1" score="INFINITY" >
     <resource_set id="colocated-set-example" sequential="true">
      <resource_ref id="A"/>
      <resource_ref id="B"/>
      <resource_ref id="C"/>
      <resource_ref id="D"/>
     </resource_set>
    </rsc_colocation>
</constraints>

If you want to use resource sets to replace a configuration of ordering constraints, consider the following two examples:

Example 6.6: A Chain of Ordered Resources
<constraints>
     <rsc_order id="order-1" first="A" then="B" />
     <rsc_order id="order-2" first="B" then="C" />
     <rsc_order id="order-3" first="C" then="D" />
</constraints>

The same purpose can be achieved by using a resource set with ordered resources:

Example 6.7: A Chain of Ordered Resources Expressed as Resource Set
<constraints>
     <rsc_order id="order-1">
     <resource_set id="ordered-set-example" sequential="true">
     <resource_ref id="A"/>
     <resource_ref id="B"/>
     <resource_ref id="C"/>
     <resource_ref id="D"/>
     </resource_set>
     </rsc_order>
</constraints>

Sets can be either ordered (sequential=true) or unordered (sequential=false). Furthermore, the require-all attribute can be used to switch between AND and OR logic.

6.5.1.1.2 Resource Sets for Colocation Constraints Without Dependencies

Sometimes it is useful to place a group of resources on the same node (defining a colocation constraint), but without having hard dependencies between the resources. For example, you want two resources to be placed on the same node, but you do not want the cluster to restart the other one if one of them fails. This can be achieved on the crm shell by using the weak bond command.

Learn how to set these weak bonds with your preferred cluster management tool:

6.5.1.2 For More Information

Learn how to add the various kinds of constraints with your preferred cluster management tool:

For more information on configuring constraints and detailed background information about the basic concepts of ordering and colocation, refer to the following documents. They are available at http://www.clusterlabs.org/doc/:

  • Pacemaker Explained, chapter Resource Constraints

  • Colocation Explained

  • Ordering Explained

6.5.2 Scores and Infinity

When defining constraints, you also need to deal with scores. Scores of all kinds are integral to how the cluster works. Practically everything from migrating a resource to deciding which resource to stop in a degraded cluster is achieved by manipulating scores in some way. Scores are calculated on a per-resource basis and any node with a negative score for a resource cannot run that resource. After calculating the scores for a resource, the cluster then chooses the node with the highest score.

INFINITY is currently defined as 1,000,000. Additions or subtractions with it stick to the following three basic rules:

  • Any value + INFINITY = INFINITY

  • Any value - INFINITY = -INFINITY

  • INFINITY - INFINITY = -INFINITY

When defining resource constraints, you specify a score for each constraint. The score indicates the value you are assigning to this resource constraint. Constraints with higher scores are applied before those with lower scores. By creating additional location constraints with different scores for a given resource, you can specify an order for the nodes that a resource will fail over to.

6.5.3 Resource Templates and Constraints

If you have defined a resource template (see Section 6.3.4, “Resource Templates”), it can be referenced in the following types of constraints:

  • order constraints,

  • colocation constraints,

  • rsc_ticket constraints (for Geo clusters).

However, colocation constraints must not contain more than one reference to a template. Resource sets must not contain a reference to a template.

Resource templates referenced in constraints stand for all primitives which are derived from that template. This means, the constraint applies to all primitive resources referencing the resource template. Referencing resource templates in constraints is an alternative to resource sets and can simplify the cluster configuration considerably. For details about resource sets, refer to Procedure 7.17, “Using a Resource Set for Constraints”.

6.5.4 Failover Nodes

A resource will be automatically restarted if it fails. If that cannot be achieved on the current node, or it fails N times on the current node, it will try to fail over to another node. Each time the resource fails, its failcount is raised. You can define a number of failures for resources (a migration-threshold), after which they will migrate to a new node. If you have more than two nodes in your cluster, the node a particular resource fails over to is chosen by the High Availability software.

However, you can specify the node a resource will fail over to by configuring one or several location constraints and a migration-threshold for that resource.

Learn how to specify failover nodes with your preferred cluster management tool:

Example 6.8: Migration Threshold—Process Flow

For example, let us assume you have configured a location constraint for resource rsc1 to preferably run on alice. If it fails there, migration-threshold is checked and compared to the failcount. If failcount >= migration-threshold then the resource is migrated to the node with the next best preference.

After the threshold has been reached, the node will no longer be allowed to run the failed resource until the resource's failcount is reset. This can be done manually by the cluster administrator or by setting a failure-timeout option for the resource.

For example, a setting of migration-threshold=2 and failure-timeout=60s would cause the resource to migrate to a new node after two failures. It would be allowed to move back (depending on the stickiness and constraint scores) after one minute.

There are two exceptions to the migration threshold concept, occurring when a resource either fails to start or fails to stop:

  • Start failures set the failcount to INFINITY and thus always cause an immediate migration.

  • Stop failures cause fencing (when stonith-enabled is set to true which is the default).

    In case there is no STONITH resource defined (or stonith-enabled is set to false), the resource will not migrate.

For details on using migration thresholds and resetting failcounts with your preferred cluster management tool:

6.5.5 Failback Nodes

A resource might fail back to its original node when that node is back online and in the cluster. To prevent a resource from failing back to the node that it was running on, or to specify a different node for the resource to fail back to, change its resource stickiness value. You can either specify resource stickiness when you are creating a resource or afterward.

Consider the following implications when specifying resource stickiness values:

Value is 0:

This is the default. The resource will be placed optimally in the system. This may mean that it is moved when a better or less loaded node becomes available. This option is almost equivalent to automatic failback, except that the resource may be moved to a node that is not the one it was previously active on.

Value is greater than 0:

The resource will prefer to remain in its current location, but may be moved if a more suitable node is available. Higher values indicate a stronger preference for a resource to stay where it is.

Value is less than 0:

The resource prefers to move away from its current location. Higher absolute values indicate a stronger preference for a resource to be moved.

Value is INFINITY:

The resource will always remain in its current location unless forced off because the node is no longer eligible to run the resource (node shutdown, node standby, reaching the migration-threshold, or configuration change). This option is almost equivalent to completely disabling automatic failback.

Value is -INFINITY:

The resource will always move away from its current location.

6.5.6 Placing Resources Based on Their Load Impact

Not all resources are equal. Some, such as Xen guests, require that the node hosting them meets their capacity requirements. If resources are placed such that their combined need exceed the provided capacity, the resources diminish in performance (or even fail).

To take this into account, the High Availability Extension allows you to specify the following parameters:

  1. The capacity a certain node provides.

  2. The capacity a certain resource requires.

  3. An overall strategy for placement of resources.

Learn how to configure these settings with your preferred cluster management tool:

A node is considered eligible for a resource if it has sufficient free capacity to satisfy the resource's requirements. The nature of the capacities is completely irrelevant for the High Availability Extension; it only makes sure that all capacity requirements of a resource are satisfied before moving a resource to a node.

To manually configure the resource's requirements and the capacity a node provides, use utilization attributes. You can name the utilization attributes according to your preferences and define as many name/value pairs as your configuration needs. However, the attribute's values must be integers.

If multiple resources with utilization attributes are grouped or have colocation constraints, the High Availability Extension takes that into account. If possible, the resources will be placed on a node that can fulfill all capacity requirements.

Note
Note: Utilization Attributes for Groups

It is impossible to set utilization attributes directly for a resource group. However, to simplify the configuration for a group, you can add a utilization attribute with the total capacity needed to any of the resources in the group.

The High Availability Extension also provides means to detect and configure both node capacity and resource requirements automatically:

The NodeUtilization resource agent checks the capacity of a node (regarding CPU and RAM). To configure automatic detection, create a clone resource of the following class, provider, and type: ocf:pacemaker:NodeUtilization. One instance of the clone should be running on each node. After the instance has started, a utilization section will be added to the node's configuration in CIB.

For automatic detection of a resource's minimal requirements (regarding RAM and CPU) the Xen resource agent has been improved. Upon start of a Xen resource, it will reflect the consumption of RAM and CPU. Utilization attributes will automatically be added to the resource configuration.

Note
Note: Different Resource Agents for Xen and libvirt

The ocf:heartbeat:Xen resource agent should not be used with libvirt, as libvirt expects to be able to modify the machine description file.

For libvirt, use the ocf:heartbeat:VirtualDomain resource agent.

Apart from detecting the minimal requirements, the High Availability Extension also allows to monitor the current utilization via the VirtualDomain resource agent. It detects CPU and RAM use of the virtual machine. To use this feature, configure a resource of the following class, provider and type: ocf:heartbeat:VirtualDomain. The following instance attributes are available: autoset_utilization_cpu and autoset_utilization_hv_memory. Both default to true. This updates the utilization values in the CIB during each monitoring cycle.

Independent of manually or automatically configuring capacity and requirements, the placement strategy must be specified with the placement-strategy property (in the global cluster options). The following values are available:

default (default value)

Utilization values are not considered. Resources are allocated according to location scoring. If scores are equal, resources are evenly distributed across nodes.

utilization

Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. However, load-balancing is still done based on the number of resources allocated to a node.

minimal

Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. An attempt is made to concentrate the resources on as few nodes as possible (to achieve power savings on the remaining nodes).

balanced

Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. An attempt is made to distribute the resources evenly, thus optimizing resource performance.

Note
Note: Configuring Resource Priorities

The available placement strategies are best-effort—they do not yet use complex heuristic solvers to always reach optimum allocation results. Ensure that resource priorities are properly set so that your most important resources are scheduled first.

Example 6.9: Example Configuration for Load-Balanced Placing

The following example demonstrates a three-node cluster of equal nodes, with four virtual machines.

node alice utilization memory="4000"
node bob utilization memory="4000"
node  charlie utilization memory="4000"
primitive xenA ocf:heartbeat:Xen utilization hv_memory="3500" \
     params xmfile="/etc/xen/shared-vm/vm1"
     meta priority="10" 
primitive xenB ocf:heartbeat:Xen utilization hv_memory="2000" \
     params xmfile="/etc/xen/shared-vm/vm2"
     meta priority="1"
primitive xenC ocf:heartbeat:Xen utilization hv_memory="2000" \
     params xmfile="/etc/xen/shared-vm/vm3"
     meta priority="1"
primitive xenD ocf:heartbeat:Xen utilization hv_memory="1000" \
     params xmfile="/etc/xen/shared-vm/vm4"
     meta priority="5"
property placement-strategy="minimal"

With all three nodes up, resource xenA will be placed onto a node first, followed by xenD. xenB and xenC would either be allocated together or one of them with xenD.

If one node failed, too little total memory would be available to host them all. xenA would be ensured to be allocated, as would xenD. However, only one of the remaining resources xenB or xenC could still be placed. Since their priority is equal, the result would still be open. To resolve this ambiguity as well, you would need to set a higher priority for either one.

6.5.7 Grouping Resources by Using Tags

Tags are a new feature that has been added to Pacemaker recently. Tags are a way to refer to multiple resources at once, without creating any colocation or ordering relationship between them. This can be useful for grouping conceptually related resources. For example, if you have several resources related to a database, create a tag called databases and add all resources related to the database to this tag. This allows you to stop or start them all with a single command.

Tags can also be used in constraints. For example, the following location constraint loc-db-prefer applies to the set of resources tagged with databases:

location loc-db-prefer databases 100: alice

Learn how to create tags with your preferred cluster management tool:

6.6 Managing Services on Remote Hosts

The possibilities for monitoring and managing services on remote hosts has become increasingly important during the last few years. SUSE Linux Enterprise High Availability Extension 11 SP3 offered fine-grained monitoring of services on remote hosts via monitoring plug-ins. The recent addition of the pacemaker_remote service now allows SUSE Linux Enterprise High Availability Extension 12 SP3 to fully manage and monitor resources on remote hosts just as if they were a real cluster node—without the need to install the cluster stack on the remote machines.

6.6.1 Monitoring Services on Remote Hosts with Monitoring Plug-ins

Monitoring of virtual machines can be done with the VM agent (which only checks if the guest shows up in the hypervisor), or by external scripts called from the VirtualDomain or Xen agent. Up to now, more fine-grained monitoring was only possible with a full setup of the High Availability stack within the virtual machines.

By providing support for monitoring plug-ins (formerly named Nagios plug-ins), the High Availability Extension now also allows you to monitor services on remote hosts. You can collect external statuses on the guests without modifying the guest image. For example, VM guests might run Web services or simple network resources that need to be accessible. With the Nagios resource agents, you can now monitor the Web service or the network resource on the guest. In case these services are not reachable anymore, the High Availability Extension will trigger a restart or migration of the respective guest.

If your guests depend on a service (for example, an NFS server to be used by the guest), the service can either be an ordinary resource, managed by the cluster, or an external service that is monitored with Nagios resources instead.

To configure the Nagios resources, the following packages must be installed on the host:

  • monitoring-plugins

  • monitoring-plugins-metadata

YaST or Zypper will resolve any dependencies on further packages, if required.

A typical use case is to configure the monitoring plug-ins as resources belonging to a resource container, which usually is a VM. The container will be restarted if any of its resources has failed. Refer to Example 6.10, “Configuring Resources for Monitoring Plug-ins” for a configuration example. Alternatively, Nagios resource agents can also be configured as ordinary resources if you want to use them for monitoring hosts or services via the network.

Example 6.10: Configuring Resources for Monitoring Plug-ins
primitive vm1 ocf:heartbeat:VirtualDomain \
    params hypervisor="qemu:///system" config="/etc/libvirt/qemu/vm1.xml" \
    op start interval="0" timeout="90" \
    op stop interval="0" timeout="90" \
    op monitor interval="10" timeout="30"
primitive vm1-sshd nagios:check_tcp \
    params hostname="vm1" port="22" \ 1
    op start interval="0" timeout="120" \ 2
    op monitor interval="10"
group g-vm1-and-services vm1 vm1-sshd \
    meta container="vm1" 3

1

The supported parameters are the same as the long options of a monitoring plug-in. Monitoring plug-ins connect to services with the parameter hostname. Therefore the attribute's value must be a resolvable host name or an IP address.

2

As it takes some time to get the guest operating system up and its services running, the start timeout of the monitoring resource must be long enough.

3

A cluster resource container of type ocf:heartbeat:Xen, ocf:heartbeat:VirtualDomain or ocf:heartbeat:lxc. It can either be a VM or a Linux Container.

The example above contains only one resource for the check_tcpplug-in, but multiple resources for different plug-in types can be configured (for example, check_http or check_udp).

If the host names of the services are the same, the hostname parameter can also be specified for the group, instead of adding it to the individual primitives. For example:

group g-vm1-and-services vm1 vm1-sshd vm1-httpd \ 
     meta container="vm1" \ 
     params hostname="vm1"

If any of the services monitored by the monitoring plug-ins fail within the VM, the cluster will detect that and restart the container resource (the VM). Which action to take in this case can be configured by specifying the on-fail attribute for the service's monitoring operation. It defaults to restart-container.

Failure counts of services will be taken into account when considering the VM's migration-threshold.

6.6.2 Managing Services on Remote Nodes with pacemaker_remote

With the pacemaker_remote service, High Availability clusters can be extended to virtual nodes or remote bare-metal machines. They do not need to run the cluster stack to become members of the cluster.

The High Availability Extension can now launch virtual environments (KVM and LXC), plus the resources that live within those virtual environments without requiring the virtual environments to run Pacemaker or Corosync.

For the use case of managing both virtual machines as cluster resources plus the resources that live within the VMs, you can now use the following setup:

  • The normal (bare-metal) cluster nodes run the High Availability Extension.

  • The virtual machines run the pacemaker_remote service (almost no configuration required on the VM's side).

  • The cluster stack on the normal cluster nodes launches the VMs and connects to the pacemaker_remote service running on the VMs to integrate them as remote nodes into the cluster.

As the remote nodes do not have the cluster stack installed, this has the following implications:

  • Remote nodes do not take part in quorum.

  • Remote nodes cannot become the DC.

  • Remote nodes are not bound by the scalability limits (Corosync has a member limit of 32 nodes).

Find more information about the remote_pacemaker service, including multiple use cases with detailed setup instructions in Pacemaker Remote—Extending High Availability into Virtual Nodes, available at http://www.clusterlabs.org/doc/.

6.7 Monitoring System Health

To prevent a node from running out of disk space and thus being unable to manage any resources that have been assigned to it, the High Availability Extension provides a resource agent, ocf:pacemaker:SysInfo. Use it to monitor a node's health with regard to disk partitions. The SysInfo RA creates a node attribute named #health_disk which will be set to red if any of the monitored disks' free space is below a specified limit.

To define how the CRM should react in case a node's health reaches a critical state, use the global cluster option node-health-strategy.

Procedure 6.2: Configuring System Health Monitoring

To automatically move resources away from a node in case the node runs out of disk space, proceed as follows:

  1. Configure an ocf:pacemaker:SysInfo resource:

    primitive sysinfo ocf:pacemaker:SysInfo \ 
         params disks="/tmp /var"1 min_disk_free="100M"2 disk_unit="M"3 \ 
         op monitor interval="15s"

    1

    Which disk partitions to monitor. For example, /tmp, /usr, /var, and /dev. To specify multiple partitions as attribute values, separate them with a blank.

    Note
    Note: / File System Always Monitored

    You do not need to specify the root partition (/) in disks. It is always monitored by default.

    2

    The minimum free disk space required for those partitions. Optionally, you can specify the unit to use for measurement (in the example above, M for megabytes is used). If not specified, min_disk_free defaults to the unit defined in the disk_unit parameter.

    3

    The unit in which to report the disk space.

  2. To complete the resource configuration, create a clone of ocf:pacemaker:SysInfo and start it on each cluster node.

  3. Set the node-health-strategy to migrate-on-red:

    property node-health-strategy="migrate-on-red"

    In case of a #health_disk attribute set to red, the policy engine adds -INF to the resources' score for that node. This will cause any resources to move away from this node. The STONITH resource will be the last one to be stopped but even if the STONITH resource is not running anymore, the node can still be fenced. Fencing has direct access to the CIB and will continue to work.

After a node's health status has turned to red, solve the issue that led to the problem. Then clear the red status to make the node eligible again for running resources. Log in to the cluster node and use one of the following methods:

  • Execute the following command:

    root # crm node status-attr NODE delete #health_disk
  • Restart Pacemaker on that node.

  • Reboot the node.

The node will be returned to service and can run resources again.

6.8 For More Information

http://crmsh.github.io/

Home page of the crm shell (crmsh), the advanced command line interface for High Availability cluster management.

http://crmsh.github.io/documentation

Holds several documents about the crm shell, including a Getting Started tutorial for basic cluster setup with crmsh and the comprehensive Manual for the crm shell. The latter is available at http://crmsh.github.io/man-2.0/. Find the tutorial at http://crmsh.github.io/start-guide/.

http://clusterlabs.org/

Home page of Pacemaker, the cluster resource manager shipped with the High Availability Extension.

http://www.clusterlabs.org/doc/

Holds several comprehensive manuals and some shorter documents explaining general concepts. For example:

  • Pacemaker Explained: Contains comprehensive and very detailed information for reference.

  • Configuring Fencing with crmsh: How to configure and use STONITH devices.

  • Colocation Explained

  • Ordering Explained

http://linux-ha.org

Home page of the The High Availability Linux Project.

7 Configuring and Managing Cluster Resources with Hawk2

Abstract

To configure and manage cluster resources, either use HA Web Konsole (Hawk2), or the crm shell (crmsh) command line utility. If you upgrade from an earlier version of SUSE® Linux Enterprise High Availability Extension where Hawk was installed, the package will be replaced with the current version, Hawk2.

Hawk2's Web-based user-interface allows you to monitor and administer your Linux cluster from non-Linux machines. Furthermore, it is the ideal solution in case your system only provides a minimal graphical user interface.

7.1 Hawk2 Requirements

Before users can log in to Hawk2, the following requirements need to be fulfilled:

  • The hawk2 package must be installed on all cluster nodes you want to connect to with Hawk2.

  • On the machine from which to access a cluster node using Hawk2, you need a (graphical) Web browser (with JavaScript and cookies enabled) to establish the connection.

  • To use Hawk2, the respective Web service must be started on the node that you want to connect to via the Web interface. See Procedure 7.1, “Starting Hawk2 Services”.

    If you have set up your cluster with the scripts from the ha-cluster-bootstrap package, the Hawk2 service is already enabled.

  • Hawk2 users must be members of the haclient group. The installation creates a Linux user named hacluster, who is added to the haclient group. When using the ha-cluster-init script for setup, a default password is set for the hacluster user.

    Before starting Hawk2, set or change the password for the hacluster user. Alternatively, create a new user which is a member of the haclient group.

    Do this on every node you will connect to with Hawk2.

Procedure 7.1: Starting Hawk2 Services
  1. On the node you want to connect to, open a shell and log in as root.

  2. Check the status of the service by entering

    root # systemctl status hawk
  3. If the service is not running, start it with

    root # systemctl start hawk

    If you want Hawk2 to start automatically at boot time, execute the following command:

    root # systemctl enable hawk

7.2 Logging In

The Hawk2 Web interface uses the HTTPS protocol and port 7630.

Instead of logging in to an individual cluster node with Hawk2, you can configure a floating, virtual IP address (IPaddr or IPaddr2) as a cluster resource. It does not need any special configuration. It allows clients to connect to the Hawk service no matter which physical node the service is running on.

When setting up the cluster with the ha-cluster-bootstrap scripts, you will be asked whether to configure a virtual IP for cluster administration.

Procedure 7.2: Logging In to the Hawk2 Web Interface
  1. On any machine, start a Web browser and enter the following URL:

    https://HAWKSERVER:7630/

    Replace HAWKSERVER with the IP address or host name of any cluster node running the Hawk Web service. If a virtual IP address has been configured for cluster administration with Hawk2, replace HAWKSERVER with the virtual IP address.

    Note
    Note: Certificate Warning

    If a certificate warning appears when you try to access the URL for the first time, a self-signed certificate is in use. Self-signed certificates are not considered trustworthy by default.

    To verify the certificate, ask your cluster operator for the certificate details.

    To proceed anyway, you can add an exception in the browser to bypass the warning.

    For information on how to replace the self-signed certificate with a certificate signed by an official Certificate Authority, refer to Replacing the Self-Signed Certificate.

  2. On the Hawk2 login screen, enter the Username and Password of the hacluster user (or of any other user that is a member of the haclient group).

  3. Click Log In.

7.3 Hawk2 Overview: Main Elements

After logging in to Hawk2, you will see a navigation bar on the left-hand side and a top-level row with several links on the right-hand side.

Note
Note: Available Functions in Hawk2

By default, users logged in as root or hacluster have full read-write access to all cluster configuration tasks. However, Access Control Lists (ACLs) can be used to define fine-grained access permissions.

If ACLs are enabled in the CRM, the available functions in Hawk2 depend on the user role and their assigned access permissions. The History Explorer in Hawk2 can only be executed by the user hacluster.

7.3.1 Left Navigation Bar

Manage
Configuration
Access Control

7.3.2 Top-Level Row

Hawk2's top-level row shows the following entries:

  • Batch: Click to switch to batch mode. This allows you to simulate and stage changes and to apply them as a single transaction. For details, see Section 7.9, “Using the Batch Mode”.

  • USERNAME: Allows you to set preferences for Hawk2 (for example, the language for the Web interface, or whether to display a warning if STONITH is disabled).

  • Help: Access the SUSE Linux Enterprise High Availability Extension documentation, read the release notes or report a bug.

  • Logout: Click to log out.

7.4 Configuring Global Cluster Options

Global cluster options control how the cluster behaves when confronted with certain situations. They are grouped into sets and can be viewed and modified with cluster management tools like Hawk2 and crmsh. The predefined values can usually be kept. However, to ensure the key functions of your cluster work correctly, you need to adjust the following parameters after basic cluster setup:

Procedure 7.3: Modifying Global Cluster Options
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Cluster Configuration.

    The Cluster Configuration screen opens. It displays the global cluster options and their current values.

    To display a short description of the parameter on the right-hand side of the screen, hover your mouse over a parameter.

    Hawk2—Cluster Configuration
    Figure 7.1: Hawk2—Cluster Configuration
  3. Check the values for no-quorum-policy and stonith-enabled and adjust them, if necessary:

    1. Set no-quorum-policy to the appropriate value. See Section 6.2.2, “Global Option no-quorum-policy for more details.

    2. If you need to disable fencing for any reason, set stonith-enabled to no. By default, it is set to true, because using STONITH devices is necessary for normal cluster operation. According to the default value, the cluster will refuse to start any resources if no STONITH resources have been configured.

      Important
      Important: No Support Without STONITH
      • You must have a node fencing mechanism for your cluster.

      • The global cluster options stonith-enabled and startup-fencing must be set to true. When you change them, you lose support.

    3. To remove a parameter from the cluster configuration, click the Minus icon next to the parameter. If a parameter is deleted, the cluster will behave as if that parameter had the default value.

    4. To add a new parameter to the cluster configuration, choose one from the drop-down box.

  4. If you need to change Resource Defaults or Operation Defaults, proceed as follows:

    1. To adjust a value, either select a different value from the drop-down box or edit the value directly.

    2. To add a new resource default or operation default, choose one from the empty drop-down box and enter a value. If there are default values, Hawk2 proposes them automatically.

    3. To remove a parameter, click the Minus icon next to it. If no values are specified for Resource Defaults and Operation Defaults, the cluster uses the default values that are documented in Section 6.3.6, “Resource Options (Meta Attributes)” and Section 6.3.8, “Resource Operations”.

  5. Confirm your changes.

7.5 Configuring Cluster Resources

A cluster administrator needs to create cluster resources for every resource or application that runs on the servers in your cluster. Cluster resources can include Web sites, mail servers, databases, file systems, virtual machines, and any other server-based applications or services you want to make available to users at all times.

For an overview of the resource types you can create, refer to Section 6.3.3, “Types of Resources”. After you have specified the resource basics (ID, class, provider, and type), Hawk2 shows the following categories:

Parameters (Instance Attributes)

Determines which instance of a service the resource controls. For more information, refer to Section 6.3.7, “Instance Attributes (Parameters)”.

When creating a resource, Hawk2 automatically shows any required parameters. Edit them to get a valid resource configuration.

Operations

Needed for resource monitoring. For more information, refer to Section 6.3.8, “Resource Operations”.

When creating a resource, Hawk2 displays the most important resource operations (monitor, start, and stop).

Meta Attributes

Tells the CRM how to treat a specific resource. For more information, refer to Section 6.3.6, “Resource Options (Meta Attributes)”.

When creating a resource, Hawk2 automatically lists the important meta attributes for that resource (for example, the target-role attribute that defines the initial state of a resource. By default, it is set to Stopped, so the resource will not start immediately).

Utilization

Tells the CRM what capacity a certain resource requires from a node. For more information, refer to Section 7.6.8, “Configuring Placement of Resources Based on Load Impact”.

You can adjust the entries and values in those categories either during resource creation or later.

7.5.1 Showing the Current Cluster Configuration (CIB)

Sometimes a cluster administrator needs to know the cluster configuration. Hawk2 can show the current configuration in crm shell syntax, as XML and as a graph. To view the cluster configuration in crm shell syntax, from the left navigation bar select Edit Configuration and click Show. To show the configuration in raw XML instead, click XML. Click Graph for a graphical representation of the nodes and resources configured in the CIB. It also shows the relationships between resources.

7.5.2 Adding Resources with the Wizard

The Hawk2 wizard is a convenient way of setting up simple resources like a virtual IP address or an SBD STONITH resource, for example. It is also useful for complex configurations that include multiple resources, like the resource configuration for a DRBD block device or an Apache Web server. The wizard guides you through the configuration steps and provides information about the parameters you need to enter.

Procedure 7.4: Using the Resource Wizard
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Wizards.

  3. Expand the individual categories by clicking the arrow down icon next to them and select the desired wizard.

  4. Follow the instructions on the screen. After the last configuration step, Verify the values you have entered.

    Hawk2 shows which actions it is going to perform and what the configuration looks like. Depending on the configuration, you might be prompted for the root password before you can Apply the configuration.

Hawk2—Wizard for Apache Web Server
Figure 7.2: Hawk2—Wizard for Apache Web Server

7.5.3 Adding Simple Resources

To create the most basic type of resource, proceed as follows:

Procedure 7.5: Adding a Primitive Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Primitive.

  3. Enter a unique Resource ID.

  4. In case a resource template exists on which you want to base the resource configuration, select the respective Template. For details about configuring templates, see Procedure 7.6, “Adding a Resource Template”.

  5. Select the resource agent Class you want to use: lsb, ocf, service, stonith, or systemd. For more information, see Section 6.3.2, “Supported Resource Agent Classes”.

  6. If you selected ocf as class, specify the Provider of your OCF resource agent. The OCF specification allows multiple vendors to supply the same resource agent.

  7. From the Type list, select the resource agent you want to use (for example, IPaddr or Filesystem). A short description for this resource agent is displayed.

    With that, you have specified the resource basics.

    Note
    Note

    The selection you get in the Type list depends on the Class (and for OCF resources also on the Provider) you have chosen.

    Hawk2—Primitive Resource
    Figure 7.3: Hawk2—Primitive Resource
  8. To keep the Parameters, Operations, and Meta Attributes as suggested by Hawk2, click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

    To adjust the parameters, operations, or meta attributes, refer to Section 7.5.5, “Modifying Resources”. To configure Utilization attributes for the resource, see Procedure 7.21, “Configuring the Capacity a Resource Requires”.

7.5.4 Adding Resource Templates

To create lots of resources with similar configurations, defining a resource template is the easiest way. After being defined, it can be referenced in primitives or in certain types of constraints. For detailed information about function and use of resource templates, refer to Section 6.5.3, “Resource Templates and Constraints”.

Procedure 7.6: Adding a Resource Template

Resource templates are configured like primitive resources.

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Template.

  3. Enter a unique Resource ID.

  4. Follow the instructions in Procedure 7.5, “Adding a Primitive Resource”, starting from Step 5.

7.5.5 Modifying Resources

If you have created a resource, you can edit its configuration at any time by adjusting parameters, operations, or meta attributes as needed.

Procedure 7.7: Modifying Parameters, Operations, or Meta Attributes for a Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. On the Hawk2 Status screen, go to the Resources list.

  3. In the Operations column, click the arrow down icon next to the resource or group you want to modify and select Edit.

    The resource configuration screen opens.

    Hawk2—Editing A Primitive Resource
    Figure 7.4: Hawk2—Editing A Primitive Resource
  4. To add a new parameter, operation, or meta attribute, select an entry from the empty drop-down box.

  5. To edit any values in the Operations category, click the Edit icon of the respective entry, enter a different value for the operation, and click Apply.

  6. When you are finished, click the Apply button in the resource configuration screen to confirm your changes to the parameters, operations, or meta attributes.

    A message at the top of the screen shows if the action has been successful.

7.5.6 Adding STONITH Resources

Important
Important: No Support Without STONITH
  • You must have a node fencing mechanism for your cluster.

  • The global cluster options stonith-enabled and startup-fencing must be set to true. When you change them, you lose support.

By default, the global cluster option stonith-enabled is set to true. If no STONITH resources have been defined, the cluster will refuse to start any resources. Configure one or more STONITH resources to complete the STONITH setup. To add a STONITH resource for SBD, for libvirt (KVM/Xen) or for vCenter/ESX Server, the easiest way is to use the Hawk2 wizard (see Section 7.5.2, “Adding Resources with the Wizard”). While STONITH resources are configured similarly to other resources, their behavior is different in some respects. For details refer to Section 10.3, “STONITH Resources and Configuration”.

Procedure 7.8: Adding a STONITH Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Primitive.

  3. Enter a unique Resource ID.

  4. From the Class list, select the resource agent class stonith.

  5. From the Type list, select the STONITH plug-in to control your STONITH device. A short description for this plug-in is displayed.

  6. Hawk2 automatically shows the required Parameters for the resource. Enter values for each parameter.

  7. Hawk2 displays the most important resource Operations and proposes default values. If you do not modify any settings here, Hawk2 adds the proposed operations and their default values when you confirm.

  8. If there is no reason to change them, keep the default Meta Attributes settings.

    Hawk2—STONITH Resource
    Figure 7.5: Hawk2—STONITH Resource
  9. Confirm your changes to create the STONITH resource.

    A message at the top of the screen shows if the action has been successful.

To complete your fencing configuration, add constraints. For more details, refer to Chapter 10, Fencing and STONITH.

7.5.7 Adding Cluster Resource Groups

Some cluster resources depend on other components or resources. They require that each component or resource starts in a specific order and runs on the same server. To simplify this configuration SUSE Linux Enterprise High Availability Extension supports the concept of groups.

Resource groups contain a set of resources that need to be located together, be started sequentially and stopped in the reverse order. For an example of a resource group and more information about groups and their properties, refer to Section 6.3.5.1, “Groups”.

Note
Note: Empty Groups

Groups must contain at least one resource, otherwise the configuration is not valid. While creating a group, Hawk2 allows you to create more primitives and add them to the group. For details, see Section 7.7.1, “Editing Resources and Groups”.

Procedure 7.9: Adding a Resource Group
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Group.

  3. Enter a unique Group ID.

  4. To define the group members, select one or multiple entries in the list of Children. Re-sort group members by dragging and dropping them into the order you want by using the handle icon on the right.

  5. If needed, modify or add Meta Attributes.

  6. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Resource Group
Figure 7.6: Hawk2—Resource Group

7.5.8 Adding Clone Resources

If you want certain resources to run simultaneously on multiple nodes in your cluster, configure these resources as clones. An example of a resource that can be configured as a clone is ocf:pacemaker:controld for cluster file systems like OCFS2. Any regular resources or resource groups can be cloned. Instances of cloned resources may behave identically. However, they may also be configured differently, depending on which node they are hosted on.

For an overview of the available types of resource clones, refer to Section 6.3.5.2, “Clones”.

Note
Note: Child Resources for Clones

Clones can either contain a primitive or a group as child resources. In Hawk2, child resources cannot be created or modified while creating a clone. Before adding a clone, create child resources and configure them as desired. For details, refer to Section 7.5.3, “Adding Simple Resources” or Section 7.5.7, “Adding Cluster Resource Groups”.

Procedure 7.10: Adding a Clone Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Clone.

  3. Enter a unique Clone ID.

  4. From the Child Resource list, select the primitive or group to use as a sub-resource for the clone.

  5. If needed, modify or add Meta Attributes.

  6. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Clone Resource
Figure 7.7: Hawk2—Clone Resource

7.5.9 Adding Multi-state Resources

Multi-state resources are a specialization of clones. They allow the instances to be in one of two operating modes (called active/passive, primary/secondary, or master/slave). Multi-state resources must contain exactly one group or one regular resource.

When configuring resource monitoring or constraints, multi-state resources have different requirements than simple resources. For details, see Pacemaker Explained, available from http://www.clusterlabs.org/doc/. Refer to section Multi-state - Resources That Have Multiple Modes.

Note
Note: Child Resources for Multi-state Resources

Multi-state resources can either contain a primitive or a group as child resources. In Hawk2, child resources cannot be created or modified while creating a multi-state resource. Before adding a multi-state resource, create child resources and configure them as desired. For details, refer to Section 7.5.3, “Adding Simple Resources” or Section 7.5.7, “Adding Cluster Resource Groups”.

Procedure 7.11: Adding a Multi-state Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Multi-state.

  3. Enter a unique Multi-state ID.

  4. From the Child Resource list, select the primitive or group to use as a sub-resource for the multi-state resource.

  5. If needed, modify or add Meta Attributes.

  6. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Multi-state Resource
Figure 7.8: Hawk2—Multi-state Resource

7.5.10 Grouping Resources by Using Tags

Tags are a way to refer to multiple resources at once, without creating any colocation or ordering relationship between them. You can use tags for grouping conceptually related resources. For example, if you have several resources related to a database, you can add all related resources to a tag named database.

All resources belonging to a tag can be started or stopped with a single command.

Procedure 7.12: Adding a Tag
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Resource › Tag.

  3. Enter a unique Tag ID.

  4. From the Objects list, select the resources you want to refer to with the tag.

  5. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Tag
Figure 7.9: Hawk2—Tag

7.5.11 Configuring Resource Monitoring

The High Availability Extension does not only detect node failures, but also when an individual resource on a node has failed. If you want to ensure that a resource is running, configure resource monitoring for it. Usually, resources are only monitored by the cluster while they are running. However, to detect concurrency violations, also configure monitoring for resources which are stopped. For resource monitoring, specify a timeout and/or start delay value, and an interval. The interval tells the CRM how often it should check the resource status. You can also set particular parameters such as timeout for start or stop operations.

Procedure 7.13: Adding and Modifying an Operation
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. Add a resource as described in Procedure 7.5, “Adding a Primitive Resource” or select an existing primitive to edit.

    Hawk2 automatically shows the most important Operations (start, stop, monitor) and proposes default values.

    To see the attributes belonging to each proposed value, hover the mouse pointer over the respective value.

  3. To change the suggested timeout values for the start or stop operation:

    1. Click the pen icon next to the operation.

    2. In the dialog that opens, enter a different value for the timeout parameter, for example 10, and confirm your change.

  4. To change the suggested interval value for the monitor operation:

    1. Click the pen icon next to the operation.

    2. In the dialog that opens, enter a different value for the monitoring interval.

    3. To configure resource monitoring in the case that the resource is stopped:

      1. Select the role entry from the empty drop-down box below.

      2. From the role drop-down box, select Stopped.

      3. Click Apply to confirm your changes and to close the dialog for the operation.

  5. Confirm your changes in the resource configuration screen. A message at the top of the screen shows if the action has been successful.

For the processes that take place if the resource monitor detects a failure, refer to Section 6.4, “Resource Monitoring”.

To view resource failures, switch to the Status screen in Hawk2 and select the resource you are interested in. In the Operations column click the arrow down icon and select Recent Events. The dialog that opens lists recent actions performed for the resource. Failures are displayed in red. To view the resource details, click the magnifier icon in the Operations column.

Hawk2—Resource Details
Figure 7.10: Hawk2—Resource Details

7.6 Configuring Constraints

After you have configured all resources, specify how the cluster should handle them correctly. Resource constraints let you specify on which cluster nodes resources can run, in which order to load resources, and what other resources a specific resource depends on.

For an overview of available types of constraints, refer to Section 6.5.1, “Types of Constraints”. When defining constraints, you also need to specify scores. For more information on scores and their implications in the cluster, see Section 6.5.2, “Scores and Infinity”.

7.6.1 Adding Location Constraints

A location constraint determines on which node a resource may be run, is preferably run, or may not be run. An example of a location constraint is to place all resources related to a certain database on the same node.

Procedure 7.14: Adding a Location Constraint

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Constraint › Location.

  3. Enter a unique Constraint ID.

  4. From the list of Resources select the resource or resources for which to define the constraint.

  5. Enter a Score. The score indicates the value you are assigning to this resource constraint. Positive values indicate the resource can run on the Node you specify in the next step. Negative values mean it should not run on that node. Constraints with higher scores are applied before those with lower scores.

    Some often-used values can also be set via the drop-down box:

    • To force the resources to run on the node, click the arrow icon and select Always. This sets the score to INFINITY.

    • If you never want the resources to run on the node, click the arrow icon and select Never. This sets the score to -INFINITY, meaning that the resources must not run on the node.

    • To set the score to 0, click the arrow icon and select Advisory. This disables the constraint. This is useful when you want to set resource discovery but do not want to constrain the resources.

  6. Select a Node.

  7. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Location Constraint
Figure 7.11: Hawk2—Location Constraint

7.6.2 Adding Colocation Constraints

A colocational constraint tells the cluster which resources may or may not run together on a node. As a colocation constraint defines a dependency between resources, you need at least two resources to create a colocation constraint.

Procedure 7.15: Adding a Colocation Constraint
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Constraint › Colocation.

  3. Enter a unique Constraint ID.

  4. Enter a Score. The score determines the location relationship between the resources. Positive values indicate that the resources should run on the same node. Negative values indicate that the resources should not run on the same node. The score will be combined with other factors to decide where to put the resource.

    Some often-used values can also be set via the drop-down box:

    • If you want to force the resources to run on the same node, click the arrow icon and select Always. This sets the score to INFINITY.

    • If you never want the resources to run on the same node, click the arrow icon and select Never. This sets the score to -INFINITY, meaning that the resources must not run on the same node.

  5. To define the resources for the constraint:

    1. From the drop-down box in the Resources category, select a resource (or a template).

      The resource is added and a new empty drop-down box appears beneath.

    2. Repeat this step to add more resources.

      As the topmost resource depends on the next resource and so on, the cluster will first decide where to put the last resource, then place the depending ones based on that decision. If the constraint cannot be satisfied, the cluster may not allow the dependent resource to run.

    3. To swap the order of resources within the colocation constraint, click the arrow up icon next to a resource to swap it with the entry above.

  6. If needed, specify further parameters for each resource (such as Started, Stopped, Master, Slave, Promote, Demote): Click the empty drop-down box next to the resource and select the desired entry.

  7. Click Create to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Colocation Constraint
Figure 7.12: Hawk2—Colocation Constraint

7.6.3 Adding Order Constraints

Order constraints define the order in which resources are started and stopped. As an order constraint defines a dependency between resources, you need at least two resources to create an order constraint.

Procedure 7.16: Adding an Order Constraint
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Add Constraint › Order.

  3. Enter a unique Constraint ID.

  4. Enter a Score. If the score is greater than zero, the order constraint is mandatory, otherwise it is optional.

    Some often-used values can also be set via the drop-down box:

    • If you want to make the order constraint mandatory, click the arrow icon and select Mandatory.

    • If you want the order constraint to be a suggestion only, click the arrow icon and select Optional.

    • Serialize: To ensure that no two stop/start actions occur concurrently for the resources, click the arrow icon and select Serialize. This makes sure that one resource must complete starting before the other can be started. A typical use case are resources that put a high load on the host during start-up.

  5. For order constraints, you can usually keep the option Symmetrical enabled. This specifies that resources are stopped in reverse order.

  6. To define the resources for the constraint:

    1. From the drop-down box in the Resources category, select a resource (or a template).

      The resource is added and a new empty drop-down box appears beneath.

    2. Repeat this step to add more resources.

      The topmost resource will start first, then the second, etc. Usually the resources will be stopped in reverse order.

    3. To swap the order of resources within the order constraint, click the arrow up icon next to a resource to swap it with the entry above.

  7. If needed, specify further parameters for each resource (like Started, Stopped, Master, Slave, Promote, Demote): Click the empty drop-down box next to the resource and select the desired entry.

  8. Confirm your changes to finish the configuration. A message at the top of the screen shows if the action has been successful.

Hawk2—Order Constraint
Figure 7.13: Hawk2—Order Constraint

7.6.4 Using Resource Sets for Constraints

As an alternative format for defining constraints, you can use Resource Sets. They have the same ordering semantics as Groups.

Procedure 7.17: Using a Resource Set for Constraints
  1. To use a resource set within a location constraint:

    1. Proceed as outlined in Procedure 7.14, “Adding a Location Constraint”, apart from Step 4: Instead of selecting a single resource, select multiple resources by pressing Ctrl or Shift and mouse click. This creates a resource set within the location constraint.

    2. To remove a resource from the location constraint, press Ctrl and click the resource again to deselect it.

  2. To use a resource set within a colocation or order constraint:

    1. Proceed as described in Procedure 7.15, “Adding a Colocation Constraint” or Procedure 7.16, “Adding an Order Constraint”, apart from the step where you define the resources for the constraint (Step 5.a or Step 6.a):

    2. Add multiple resources.

    3. To create a resource set, click the chain icon next to a resource to link it to the resource above. A resource set is visualized by a frame around the resources belonging to a set.

    4. You can combine multiple resources in a resource set or create multiple resource sets.

      Hawk2—Two Resource Sets in a Colocation Constraint
      Figure 7.14: Hawk2—Two Resource Sets in a Colocation Constraint
    5. To unlink a resource from the resource above, click the scissors icon next to the resource.

  3. Confirm your changes to finish the constraint configuration.

7.6.5 For More Information

For more information on configuring constraints and detailed background information about the basic concepts of ordering and colocation, refer to the documentation available at http://www.clusterlabs.org/doc/:

  • Pacemaker Explained, chapter Resource Constraints

  • Colocation Explained

  • Ordering Explained

7.6.6 Specifying Resource Failover Nodes

A resource will be automatically restarted if it fails. If that cannot be achieved on the current node, or it fails N times on the current node, it will try to fail over to another node. You can define several failures for resources (a migration-threshold), after which they will migrate to a new node. If you have more than two nodes in your cluster, the node to which a particular resource fails over is chosen by the High Availability software.

You can specify a specific node to which a resource will fail over by proceeding as follows:

Procedure 7.18: Specifying a Failover Node
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. Configure a location constraint for the resource as described in Procedure 7.14, “Adding a Location Constraint”.

  3. Add the migration-threshold meta attribute to the resource as described in Procedure 7.7: Modifying Parameters, Operations, or Meta Attributes for a Resource, Step 4 and enter a value for the migration-threshold. The value should be positive and less than INFINITY.

  4. If you want to automatically expire the failcount for a resource, add the failure-timeout meta attribute to the resource as described in Procedure 7.5: Adding a Primitive Resource, Step 4 and enter a Value for the failure-timeout.

  5. If you want to specify additional failover nodes with preferences for a resource, create additional location constraints.

The process flow regarding migration thresholds and failcounts is demonstrated in Example 6.8, “Migration Threshold—Process Flow”.

Instead of letting the failcount for a resource expire automatically, you can also clean up failcounts for a resource manually at any time. Refer to Section 7.7.3, “Cleaning Up Resources” for details.

7.6.7 Specifying Resource Failback Nodes (Resource Stickiness)

A resource may fail back to its original node when that node is back online and in the cluster. To prevent this or to specify a different node for the resource to fail back to, change the stickiness value of the resource. You can either specify the resource stickiness when creating it or afterward.

For the implications of different resource stickiness values, refer to Section 6.5.5, “Failback Nodes”.

Procedure 7.19: Specifying Resource Stickiness
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. Add the resource-stickiness meta attribute to the resource as described in Procedure 7.7: Modifying Parameters, Operations, or Meta Attributes for a Resource, Step 4.

  3. Specify a value between -INFINITY and INFINITY for resource-stickiness.

7.6.8 Configuring Placement of Resources Based on Load Impact

Not all resources are equal. Some, such as Xen guests, require that the node hosting them meets their capacity requirements. If resources are placed so that their combined needs exceed the provided capacity, the performance of the resources diminishes or they fail.

To take this into account, the High Availability Extension allows you to specify the following parameters:

  1. The capacity a certain node provides.

  2. The capacity a certain resource requires.

  3. An overall strategy for placement of resources.

For more details and a configuration example, refer to Section 6.5.6, “Placing Resources Based on Their Load Impact”.

Utilization attributes are used to configure both the resource's requirements and the capacity a node provides. You first need to configure a node's capacity before you can configure the capacity a resource requires.

Procedure 7.20: Configuring the Capacity a Node Provides
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status.

  3. On the Nodes tab, select the node whose capacity you want to configure.

  4. In the Operations column, click the arrow down icon and select Edit.

    The Edit Node screen opens.

  5. Below Utilization, enter a name for a utilization attribute into the empty drop-down box.

    The name can be arbitrary (for example, RAM_in_GB).

  6. Click the Add icon to add the attribute.

  7. In the empty text box next to the attribute, enter an attribute value. The value must be an integer.

  8. Add as many utilization attributes as you need and add values for all of them.

  9. Confirm your changes. A message at the top of the screen shows if the action has been successful.

Procedure 7.21: Configuring the Capacity a Resource Requires

Configure the capacity a certain resource requires from a node either when creating a primitive resource or when editing an existing primitive resource.

Before you can add utilization attributes to a resource, you need to have set utilization attributes for your cluster nodes as described in Procedure 7.20.

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. To add a utilization attribute to an existing resource: Go to Manage › Status and open the resource configuration dialog as described in Section 7.7.1, “Editing Resources and Groups”.

    If you create a new resource: Go to Configuration › Add Resource and proceed as described in Section 7.5.3, “Adding Simple Resources”.

  3. In the resource configuration dialog, go to the Utilization category.

  4. From the empty drop-down box, select one of the utilization attributes that you have configured for the nodes in Procedure 7.20.

  5. In the empty text box next to the attribute, enter an attribute value. The value must be an integer.

  6. Add as many utilization attributes as you need and add values for all of them.

  7. Confirm your changes. A message at the top of the screen shows if the action has been successful.

After you have configured the capacities your nodes provide and the capacities your resources require, set the placement strategy in the global cluster options. Otherwise the capacity configurations have no effect. Several strategies are available to schedule the load: for example, you can concentrate it on as few nodes as possible, or balance it evenly over all available nodes. For more information, refer to Section 6.5.6, “Placing Resources Based on Their Load Impact”.

Procedure 7.22: Setting the Placement Strategy
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Cluster Configuration to open the respective screen. It shows global cluster options and resource and operation defaults.

  3. From the empty drop-down box in the upper part of the screen, select placement-strategy.

    By default, its value is set to Default, which means that utilization attributes and values are not considered.

  4. Depending on your requirements, set Placement Strategy to the appropriate value.

  5. Confirm your changes.

7.7 Managing Cluster Resources

In addition to configuring your cluster resources, Hawk2 allows you to manage existing resources from the Status screen. For a general overview of the screen refer to Section 7.8.1, “Monitoring a Single Cluster”.

7.7.1 Editing Resources and Groups

In case you need to edit existing resources, go to the Status screen. In the Operations column, click the arrow down icon next to the resource or group you want to modify and select Edit.

The editing screen appears. If you edit a primitive resource, the following operations are available:

Operations for Primitives
  • Copying the resource.

  • Renaming the resource (changing its ID).

  • Deleting the resource.

If you edit a group, the following operations are available:

Operations for Groups
  • Creating a new primitive which will be added to this group.

  • Renaming the group (changing its ID).

  • Re-sort group members by dragging and dropping them into the order you want using the handle icon on the right.

7.7.2 Starting Resources

Before you start a cluster resource, make sure it is set up correctly. For example, if you use an Apache server as a cluster resource, set up the Apache server first. Complete the Apache configuration before starting the respective resource in your cluster.

Note
Note: Do Not Touch Services Managed by the Cluster

When managing a resource via the High Availability Extension, the resource must not be started or stopped otherwise (outside of the cluster, for example manually or on boot or reboot). The High Availability Extension software is responsible for all service start or stop actions.

However, if you want to check if the service is configured properly, start it manually, but make sure that it is stopped again before the High Availability Extension takes over.

For interventions in resources that are currently managed by the cluster, set the resource to maintenance mode first. For details, see Procedure 16.5, “Putting a Resource Into Maintenance Mode with Hawk2”.

When creating a resource with Hawk2, you can set its initial state with the target-role meta attribute. If you set its value to stopped, the resource does not start automatically after being created.

Procedure 7.23: Starting A New Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status. The list of Resources also shows the Status.

  3. Select the resource to start. In its Operations column click the Start icon. To continue, confirm the message that appears.

    When the resource has started, Hawk2 changes the resource's Status to green and shows on which node it is running.

7.7.3 Cleaning Up Resources

A resource will be automatically restarted if it fails, but each failure increases the resource's failcount.

If a migration-threshold has been set for the resource, the node will no longer run the resource when the number of failures reaches the migration threshold.

A resource's failcount can either be reset automatically (by setting a failure-timeout option for the resource) or it can be reset manually as described below.

Procedure 7.24: Cleaning Up A Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status. The list of Resources also shows the Status.

  3. Go to the resource to clean up. In the Operations column click the arrow down button and select Cleanup. To continue, confirm the message that appears.

    This executes the command crm resource cleanup and cleans up the resource on all nodes.

7.7.4 Removing Cluster Resources

If you need to remove a resource from the cluster, follow the procedure below to avoid configuration errors:

Procedure 7.25: Removing a Cluster Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. Clean up the resource on all nodes as described in Procedure 7.24, “Cleaning Up A Resource”.

  3. Stop the resource:

    1. In the left navigation bar, select Status. The list of Resources also shows the Status.

    2. In the Operations column click the Stop button next to the resource.

    3. To continue, confirm the message that appears.

      The Status column will reflect the change when the resource is stopped.

  4. Delete the resource:

    1. In the left navigation bar, select Edit Configuration.

    2. In the list of Resources, go to the respective resource. From the Operations column click the Delete icon next to the resource.

    3. To continue, confirm the message that appears.

7.7.5 Migrating Cluster Resources

As mentioned in Section 7.6.6, “Specifying Resource Failover Nodes”, the cluster will fail over (migrate) resources automatically in case of software or hardware failures—according to certain parameters you can define (for example, migration threshold or resource stickiness). You can also manually migrate a resource to another node in the cluster. Or you decide to move the resource away from the current node and let the cluster decide where to put it.

Procedure 7.26: Manually Migrating a Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status. The list of Resources also shows the Status.

  3. In the list of Resources, select the respective resource.

  4. In the Operations column click the arrow down button and select Migrate.

  5. In the window that opens you have the following choices:

    • Away from current node: This creates a location constraint with a -INFINITY score for the current node.

    • Alternatively, you can move the resource to another node. This creates a location constraint with an INFINITY score for the destination node.

  6. Confirm your choice.

To allow a resource to move back again, proceed as follows:

Procedure 7.27: Unmigrating a Resource
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status. The list of Resources also shows the Status.

  3. In the list of Resources, go to the respective resource.

  4. In the Operations column click the arrow down button and select Unmigrate. To continue, confirm the message that appears.

    Hawk2 uses the crm_resource  -U command. The resource can move back to its original location or it may stay where it is (depending on resource stickiness).

For more information, see Pacemaker Explained, available from http://www.clusterlabs.org/doc/. Refer to section Resource Migration.

7.8 Monitoring Clusters

Hawk2 has different screens for monitoring single clusters and multiple clusters: the Status and the Dashboard screen.

7.8.1 Monitoring a Single Cluster

To monitor a single cluster, use the Status screen. After you have logged in to Hawk2, the Status screen is displayed by default. An icon in the upper right corner shows the cluster status at a glance. For further details, have a look at the following categories:

Errors

If errors have occurred, they are shown at the top of the page.

Resources

Shows the configured resources including their Status, Name (ID), Location (node on which they are running), and resource agent Type. From the Operations column, you can start or stop a resource, trigger several actions, or view details. Actions that can be triggered include setting the resource to maintenance mode (or removing maintenance mode), migrating it to a different node, cleaning up the resource, showing any recent events, or editing the resource.

Nodes

Shows the nodes belonging to the cluster site you are logged in to, including the nodes' Status and Name. In the Maintenance and Standby columns, you can set or remove the maintenance or standby flag for a node. The Operations column allows you to view recent events for the node or further details: for example, if a utilization, standby or maintenance attribute is set for the respective node.

Tickets

Only shown if tickets have been configured (for use with Geo clustering).

Hawk2—Cluster Status
Figure 7.15: Hawk2—Cluster Status

7.8.2 Monitoring Multiple Clusters

To monitor multiple clusters, use the Hawk2 Dashboard. The cluster information displayed in the Dashboard screen is stored on the server side. It is synchronized between the cluster nodes (if passwordless SSH access between the cluster nodes has been configured). For details, see Section D.2, “Configuring a Passwordless SSH Account”. However, the machine running Hawk2 does not even need to be part of any cluster for that purpose—it can be a separate, unrelated system.

In addition to the general Hawk2 Requirements, the following prerequisites need to be fulfilled to monitor multiple clusters with Hawk2:

Prerequisites
  • All clusters to be monitored from Hawk2's Dashboard must be running SUSE Linux Enterprise High Availability Extension 12 SP3.

  • If you did not replace the self-signed certificate for Hawk2 on every cluster node with your own certificate (or a certificate signed by an official Certificate Authority) yet, do the following: Log in to Hawk2 on every node in every cluster at least once. Verify the certificate (or add an exception in the browser to bypass the warning). Otherwise Hawk2 cannot connect to the cluster.

Procedure 7.28: Monitoring Multiple Clusters with the Dashboard
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Dashboard.

    Hawk2 shows an overview of the resources and nodes on the current cluster site. In addition, it shows any Tickets that have been configured for use with a Geo cluster. If you need information about the icons used in this view, click Legend. To search for a resource ID, enter the name (ID) into the Search text box. To only show specific nodes, click the filter icon and select a filtering option.

    Hawk2 Dashboard with One Cluster Site (amsterdam)
    Figure 7.16: Hawk2 Dashboard with One Cluster Site (amsterdam)
  3. To add dashboards for multiple clusters:

    1. Click Add Cluster.

    2. Enter the Cluster name with which to identify the cluster in the Dashboard. For example, berlin.

    3. Enter the fully qualified host name of one of the nodes in the second cluster. For example, charlie.

    4. Click Add. Hawk2 will display a second tab for the newly added cluster site with an overview of its nodes and resources.

      Note
      Note: Connection Error

      If instead you are prompted to log in to this node by entering a password, you probably did not connect to this node yet and have not replaced the self-signed certificate. In that case, even after entering the password, the connection will fail with the following message: Error connecting to server. Retrying every 5 seconds... '.

      To proceed, see Replacing the Self-Signed Certificate.

  4. To view more details for a cluster site or to manage it, switch to the site's tab and click the chain icon.

    Hawk2 opens the Status view for this site in a new browser window or tab. From there, you can administer this part of the Geo cluster.

  5. To remove a cluster from the dashboard, click the x icon on the right-hand side of the cluster's details.

7.9 Using the Batch Mode

Hawk2 provides a Batch Mode, including a cluster simulator. It can be used for the following:

  • Staging changes to the cluster and applying them as a single transaction, instead of having each change take effect immediately.

  • Simulating changes and cluster events, for example, to explore potential failure scenarios.

For example, batch mode can be used when creating groups of resources that depend on each other. Using batch mode, you can avoid applying intermediate or incomplete configurations to the cluster.

While batch mode is enabled, you can add or edit resources and constraints or change the cluster configuration. It is also possible to simulate events in the cluster, including nodes going online or offline, resource operations and tickets being granted or revoked. See Procedure 7.30, “Injecting Node, Resource or Ticket Events” for details.

The cluster simulator runs automatically after every change and shows the expected outcome in the user interface. For example, this also means: If you stop a resource while in batch mode, the user interface shows the resource as stopped—while actually, the resource is still running.

Important
Important: Wizards and Changes to the Live System

Some wizards include actions beyond mere cluster configuration. When using those wizards in batch mode, any changes that go beyond cluster configuration would be applied to the live system immediately.

Therefore wizards that require root permission cannot be executed in batch mode.

Procedure 7.29: Working with the Batch Mode
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. To activate the batch mode, select Batch from the top-level row.

    An additional bar appears below the top-level row. It indicates that batch mode is active and contains links to actions that you can execute in batch mode.

    Hawk2 Batch Mode Activated
    Figure 7.17: Hawk2 Batch Mode Activated
  3. While batch mode is active, perform any changes to your cluster, like adding or editing resources and constraints or editing the cluster configuration.

    The changes will be simulated and shown in all screens.

  4. To view details of the changes you have made, select Show from the batch mode bar. The Batch Mode window opens.

    For any configuration changes it shows the difference between the live state and the simulated changes in crmsh syntax: Lines starting with a - character represent the current state whereas lines starting with + show the proposed state.

  5. To inject events or view even more details, see Procedure 7.30. Otherwise Close the window.

  6. Choose to either Discard or Apply the simulated changes and confirm your choice. This also deactivates batch mode and takes you back to normal mode.

When running in batch mode, Hawk2 also allows you to inject Node Events and Resource Events.

Node Events

Let you change the state of a node. Available states are online, offline, and unclean.

Resource Events

Let you change some properties of a resource. For example, you can set an operation (like start, stop, monitor), the node it applies to, and the expected result to be simulated.

Ticket Events

Let you test the impact of granting and revoking tickets (used for Geo clusters).

Procedure 7.30: Injecting Node, Resource or Ticket Events
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. If batch mode is not active yet, click Batch at the top-level row to switch to batch mode.

  3. In the batch mode bar, click Show to open the Batch Mode window.

  4. To simulate a status change of a node:

    1. Click Inject › Node Event.

    2. Select the Node you want to manipulate and select its target State.

    3. Confirm your changes. Your event is added to the queue of events listed in the Batch Mode dialog.

  5. To simulate a resource operation:

    1. Click Inject › Resource Event.

    2. Select the Resource you want to manipulate and select the Operation to simulate.

    3. If necessary, define an Interval.

    4. Select the Node on which to run the operation and the targeted Result. Your event is added to the queue of events listed in the Batch Mode dialog.

    5. Confirm your changes.

  6. To simulate a ticket action:

    1. Click Inject › Ticket Event.

    2. Select the Ticket you want to manipulate and select the Action to simulate.

    3. Confirm your changes. Your event is added to the queue of events listed in the Batch Mode dialog.

  7. The Batch Mode dialog (Figure 7.18) shows a new line per injected event. Any event listed here is simulated immediately and is reflected on the Status screen.

    If you have made any configuration changes, too, the difference between the live state and the simulated changes is shown below the injected events.

    Hawk2 Batch Mode—Injected Invents and Configuration Changes
    Figure 7.18: Hawk2 Batch Mode—Injected Invents and Configuration Changes
  8. To remove an injected event, click the Remove icon next to it. Hawk2 updates the Status screen accordingly.

  9. To view more details about the simulation run, click Simulator and choose one of the following:

    Summary

    Shows a detailed summary.

    CIB (in)/CIB (out)

    CIB (in) shows the initial CIB state. CIB (out) shows what the CIB would look like after the transition.

    Transition Graph

    Shows a graphical representation of the transition.

    Transition

    Shows an XML representation of the transition.

  10. If you have reviewed the simulated changes, close the Batch Mode window.

  11. To leave the batch mode, either Apply or Discard the simulated changes.

7.10 Viewing the Cluster History

Hawk2 provides the following possibilities to view past events on the cluster (on different levels and in varying detail):

7.10.1 Viewing Recent Events of Nodes or Resources

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Status. It lists Resources and Nodes.

  3. To view recent events of a resource:

    1. Click Resources and select the respective resource.

    2. In the Operations column for the resource, click the arrow down button and select Recent events.

      Hawk2 opens a new window and displays a table view of the latest events.

  4. To view recent events of a node:

    1. Click Nodes and select the respective node.

    2. In the Operations column for the node, select Recent events.

      Hawk2 opens a new window and displays a table view of the latest events.

7.10.2 Using the History Explorer for Cluster Reports

From the left navigation bar, select History to access the History Explorer. The History Explorer allows you to create detailed cluster reports and view transition information. It provides the following options:

Generate

Create a cluster report for a certain time. Hawk2 calls the crm report command to generate the report.

Upload

Allows you to upload crm report archives that have either been created with the crm shell directly or even on a different cluster.

After reports have been generated or uploaded, they are shown below Reports. From the list of reports, you can show a report's details, download or delete the report.

Hawk2—History Explorer Main View
Figure 7.19: Hawk2—History Explorer Main View
Procedure 7.31: Generating or Uploading a Cluster Report
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select History.

    The History Explorer screen opens in the Generate view. By default, the suggested time frame for a report is the last hour.

  3. To create a cluster report:

    1. To immediately start a report, click Generate.

    2. To modify the time frame for the report, click anywhere on the suggested time frame and select another option from the drop-down box. You can also enter a Custom start date, end date and hour, respectively. To start the report, click Generate.

      After the report has finished, it is shown below Reports.

  4. To upload a cluster report, the crm report archive must be located on a file system that you can access with Hawk2. Proceed as follows:

    1. Switch to the Upload tab.

    2. Browse for the cluster report archive and click Upload.

      After the report is uploaded, it is shown below Reports.

  5. To download or delete a report, click the respective icon next to the report in the Operations column.

  6. To view Report Details in History Explorer, click the report's name or select Show from the Operations column.

  7. Return to the list of reports by clicking the Reports button.

Report Details in History Explorer
  • Name of the report.

  • Start time of the report.

  • End time of the report.

  • Number of transitions plus time line of all transitions in the cluster that are covered by the report. To learn how to view more details for a transition, see Section 7.10.3.

  • Node events.

  • Resource events.

7.10.3 Viewing Transition Details in the History Explorer

For each transition, the cluster saves a copy of the state which it provides as input to the policy engine (PE). The path to this archive is logged. All pe-input* files are generated on the Designated Coordinator (DC). As the DC can change in a cluster, there may be pe-input* files from several nodes. Any pe-input* files show what the PE planned to do.

In Hawk2, you can display the name of each pe-input* file plus the time and node on which it was created. In addition, the History Explorer can visualize the following details, based on the respective pe-input* file:

Transition Details in the History Explorer
Details

Shows snippets of logging data that belongs to the transition. Displays the output of the following command (including the resource agents' log messages):

crm history transition peinput
Configuration

Shows the cluster configuration at the time that the pe-input* file was created.

Diff

Shows the differences of configuration and status between the selected pe-input* file and the following one.

Log

Shows snippets of logging data that belongs to the transition. Displays the output of the following command:

crm history transition log peinput

This includes details from the pengine, crmd, and lrmd.

Graph

Shows a graphical representation of the transition. If you click Graph, the PE is re-invoked (using the pe-input* files), and generates a graphical visualization of the transition.

Procedure 7.32: Viewing Transition Details
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select History.

    If reports have already been generated or uploaded, they are shown in the list of Reports. Otherwise generate or upload a report as described in Procedure 7.31.

  3. Click the report's name or select Show from the Operations column to open the Report Details in History Explorer.

  4. To access the transition details, you need to select a transition point in the transition time line that is shown below. Use the Previous and Next icons and the Zoom In and Zoom Out icons to find the transition that you are interested in.

  5. To display the name of a pe-input* file plus the time and node on which it was created, hover the mouse pointer over a transition point in the time line.

  6. To view the Transition Details in the History Explorer, click the transition point for which you want to know more.

  7. To show Details, Configuration, Diff, Logs or Graph, click the respective buttons to show the content described in Transition Details in the History Explorer.

  8. To return to the list of reports, click the Reports button.

7.11 Verifying Cluster Health

Hawk2 provides a wizard which checks and detects issues with your cluster. After the analysis is complete, Hawk2 creates a cluster report with further details. To verify cluster health and generate the report, Hawk2 requires passwordless SSH access between the nodes. Otherwise it can only collect data from the current node. If you have set up your cluster with the bootstrap scripts, provided by the ha-cluster-bootstrap package, passwordless SSH access is already configured. In case you need to configure it manually, see Section D.2, “Configuring a Passwordless SSH Account”.

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. From the left navigation bar, select Wizards.

  3. Expand the Basic category.

  4. Select the Verify health and configuration wizard.

  5. Confirm with Verify.

  6. Enter the root password for your cluster and click Apply. Hawk2 will generate the report.

8 Configuring and Managing Cluster Resources (Command Line)

Abstract

To configure and manage cluster resources, either use the crm shell (crmsh) command line utility or HA Web Konsole (Hawk2), a Web-based user interface.

This chapter introduces crm, the command line tool and covers an overview of this tool, how to use templates, and mainly configuring and managing cluster resources: creating basic and advanced types of resources (groups and clones), configuring constraints, specifying failover nodes and failback nodes, configuring resource monitoring, starting, cleaning up or removing resources, and migrating resources manually.

Note
Note: User Privileges

Sufficient privileges are necessary to manage a cluster. The crm command and its subcommands need to be run either as root user or as the CRM owner user (typically the user hacluster).

However, the user option allows you to run crm and its subcommands as a regular (unprivileged) user and to change its ID using sudo whenever necessary. For example, with the following command crm will use hacluster as the privileged user ID:

root # crm options user hacluster

Note that you need to set up /etc/sudoers so that sudo does not ask for a password.

8.1 crmsh—Overview

The crm command has several subcommands which manage resources, CIBs, nodes, resource agents, and others. It offers a thorough help system with embedded examples. All examples follow a naming convention described in Appendix B.

Tip
Tip: Distinguish Between Shell Prompt and Interactive crm Prompt

To make all the code and examples more readable, this chapter uses the following notations between shell prompts and the interactive crm prompt:

  • Shell prompt for user root:

    root # 
  • Interactive crmsh prompt (displayed in green, if terminal supports colors):

    crm(live)# 

8.1.1 Getting Help

Help can be accessed in several ways:

  • To output the usage of crm and its command line options:

    root # crm --help
  • To give a list of all available commands:

    root # crm help
  • To access other help sections, not just the command reference:

    root # crm help topics
  • To view the extensive help text of the configure subcommand:

    root # crm configure help
  • To print the syntax, its usage, and examples of the group subcommand of configure:

    root # crm configure help group

    This is the same:

    root # crm help configure group

Almost all output of the help subcommand (do not mix it up with the --help option) opens a text viewer. This text viewer allows you to scroll up or down and read the help text more comfortably. To leave the text viewer, press the Q key.

Tip
Tip: Use Tab Completion in Bash and Interactive Shell

The crmsh supports full tab completion in Bash directly, not only for the interactive shell. For example, typing crm help config→| will complete the word like in the interactive shell.

8.1.2 Executing crmsh's Subcommands

The crm command itself can be used in the following ways:

  • Directly:  Concatenate all subcommands to crm, press Enter and you see the output immediately. For example, enter crm help ra to get information about the ra subcommand (resource agents).

    It is possible to abbreviate subcommands as long as they are unique. For example, you can shorten status as st and crmsh will know what you have meant.

    Another feature is to shorten parameters. Usually, you add parameters through the params keyword. You can leave out the params section if it is the first and only section. For example, this line:

    root # crm primitive ipaddr ocf:heartbeat:IPaddr2 params ip=192.168.0.55

    is equivalent to this line:

    root # crm primitive ipaddr ocf:heartbeat:IPaddr2 ip=192.168.0.55
  • As crm Shell Script:  Crm shell scripts contain subcommands of crm. For more information, see Section 8.1.4, “Using crmsh's Shell Scripts”.

  • As crmsh Cluster Scripts: These are a collection of metadata, references to RPM packages, configuration files, and crmsh subcommands bundled under a single, yet descriptive name. They are managed through the crm script command.

    Do not confuse them with crmsh shell scripts: although both share some common objectives, the crm shell scripts only contain subcommands whereas cluster scripts incorporate much more than a simple enumeration of commands. For more information, see Section 8.1.5, “Using crmsh's Cluster Scripts”.

  • Interactive as Internal Shell:  Type crm to enter the internal shell. The prompt changes to crm(live). With help you can get an overview of the available subcommands. As the internal shell has different levels of subcommands, you can enter one by typing this subcommand and press Enter.

    For example, if you type resource you enter the resource management level. Your prompt changes to crm(live)resource#. If you want to leave the internal shell, use the commands quit, bye, or exit. If you need to go one level back, use back, up, end, or cd.

    You can enter the level directly by typing crm and the respective subcommand(s) without any options and press Enter.

    The internal shell supports also tab completion for subcommands and resources. Type the beginning of a command, press →| and crm completes the respective object.

In addition to previously explained methods, crmsh also supports synchronous command execution. Use the -w option to activate it. If you have started crm without -w, you can enable it later with the user preference's wait set to yes (options wait yes). If this option is enabled, crm waits until the transition is finished. Whenever a transaction is started, dots are printed to indicate progress. Synchronous command execution is only applicable for commands like resource start.

Note
Note: Differentiate Between Management and Configuration Subcommands

The crm tool has management capability (the subcommands resource and node) and can be used for configuration (cib, configure).

The following subsections give you an overview of some important aspects of the crm tool.

8.1.3 Displaying Information about OCF Resource Agents

As you need to deal with resource agents in your cluster configuration all the time, the crm tool contains the ra command. Use it to show information about resource agents and to manage them (for additional information, see also Section 6.3.2, “Supported Resource Agent Classes”):

root # crm ra
crm(live)ra# 

The command classes lists all classes and providers:

crm(live)ra# classes
 lsb
 ocf / heartbeat linbit lvm2 ocfs2 pacemaker
 service
 stonith
 systemd

To get an overview of all available resource agents for a class (and provider) use the list command:

crm(live)ra# list ocf
AoEtarget           AudibleAlarm        CTDB                ClusterMon
Delay               Dummy               EvmsSCC             Evmsd
Filesystem          HealthCPU           HealthSMART         ICP
IPaddr              IPaddr2             IPsrcaddr           IPv6addr
LVM                 LinuxSCSI           MailTo              ManageRAID
ManageVE            Pure-FTPd           Raid1               Route
SAPDatabase         SAPInstance         SendArp             ServeRAID
...

An overview of a resource agent can be viewed with info:

crm(live)ra# info ocf:linbit:drbd
This resource agent manages a DRBD* resource
as a master/slave resource. DRBD is a shared-nothing replicated storage
device. (ocf:linbit:drbd)

Master/Slave OCF Resource Agent for DRBD

Parameters (* denotes required, [] the default):

drbd_resource* (string): drbd resource name
    The name of the drbd resource from the drbd.conf file.

drbdconf (string, [/etc/drbd.conf]): Path to drbd.conf
    Full path to the drbd.conf file.

Operations' defaults (advisory minimum):

    start         timeout=240
    promote       timeout=90 
    demote        timeout=90 
    notify        timeout=90 
    stop          timeout=100
    monitor_Slave_0 interval=20 timeout=20 start-delay=1m
    monitor_Master_0 interval=10 timeout=20 start-delay=1m

Leave the viewer by pressing Q.

Tip
Tip: Use crm Directly

In the former example we used the internal shell of the crm command. However, you do not necessarily need to use it. You get the same results if you add the respective subcommands to crm. For example, you can list all the OCF resource agents by entering crm ra list ocf in your shell.

8.1.4 Using crmsh's Shell Scripts

The crmsh shell scripts provide a convenient way to enumerate crmsh subcommands into a file. This makes it easy to comment specific lines or to replay them later. Keep in mind that a crmsh shell script can contain only crmsh subcommands. Any other commands are not allowed.

Before you can use a crmsh shell script, create a file with specific commands. For example, the following file prints the status of the cluster and gives a list of all nodes:

Example 8.1: A Simple crmsh Shell Script
# A small example file with some crm subcommands
status
node list

Any line starting with the hash symbol (#) is a comment and is ignored. If a line is too long, insert a backslash (\) at the end and continue in the next line. It is recommended to indent lines that belong to a certain subcommand to improve readability.

To use this script, use one of the following methods:

root # crm -f example.cli
root # crm < example.cli

8.1.5 Using crmsh's Cluster Scripts

Collecting information from all cluster nodes and deploying any changes is a key cluster administration task. Instead of performing the same procedures manually on different nodes (which is error-prone), you can use the crmsh cluster scripts.

Do not confuse them with the crmsh shell scripts, which are explained in Section 8.1.4, “Using crmsh's Shell Scripts”.

In contrast to crmsh shell scripts, cluster scripts performs additional tasks like:

  • Installing software that is required for a specific task.

  • Creating or modifying any configuration files.

  • Collecting information and reporting potential problems with the cluster.

  • Deploying the changes to all nodes.

crmsh cluster scripts do not replace other tools for managing clusters—they provide an integrated way to perform the above tasks across the cluster. Find detailed information at http://crmsh.github.io/scripts/.

8.1.5.1 Usage

To get a list of all available cluster scripts, run:

root # crm script list

To view the components of a script, use the show command and the name of the cluster script, for example:

root # crm script show mailto
mailto (Basic)
MailTo

 This is a resource agent for MailTo. It sends email to a sysadmin
whenever  a takeover occurs.

1. Notifies recipients by email in the event of resource takeover

  id (required)  (unique)
      Identifier for the cluster resource
  email (required)
      Email address
  subject
      Subject

The output of show contains a title, a short description, and a procedure. Each procedure is divided into a series of steps, performed in the given order.

Each step contains a list of required and optional parameters, along with a short description and its default value.

Each cluster script understands a set of common parameters. These parameters can be passed to any script:

Table 8.1: Common Parameters
ParameterArgumentDescription
actionINDEXIf set, only execute a single action (index, as returned by verify)
dry_runBOOLIf set, simulate execution only (default: no)
nodesLISTList of nodes to execute the script for
portNUMBERPort to connect to
statefileFILEWhen single-stepping, the state is saved in the given file
sudoBOOLIf set, crm will prompt for a sudo password and use sudo where appropriate (default: no)
timeoutNUMBERExecution timeout in seconds (default: 600)
userUSERRun script as the given user

8.1.5.2 Verifying and Running a Cluster Script

Before running a cluster script, review the actions that it will perform and verify its parameters to avoid problems. A cluster script can potentially perform a series of actions and may fail for various reasons. Thus, verifying your parameters before running it helps to avoid problems.

For example, the mailto resource agent requires a unique identifier and an e-mail address. To verify these parameters, run:

root # crm script verify mailto id=sysadmin email=tux@example.org
1. Ensure mail package is installed

        mailx

2. Configure cluster resources

        primitive sysadmin ocf:heartbeat:MailTo
                email="tux@example.org"
                op start timeout="10"
                op stop timeout="10"
                op monitor interval="10" timeout="10"

        clone c-sysadmin sysadmin

The verify prints the steps and replaces any placeholders with your given parameters. If verify finds any problems, it will report it. If everything is ok, replace the verify command with run:

root # crm script run mailto id=sysadmin email=tux@example.org
INFO: MailTo
INFO: Nodes: alice, bob
OK: Ensure mail package is installed
OK: Configure cluster resources

Check whether your resource is integrated into your cluster with crm status:

root # crm status
[...]
 Clone Set: c-sysadmin [sysadmin]
     Started: [ alice bob ]

8.1.6 Using Configuration Templates

Note
Note: Deprecation Notice

The use of configuration templates is deprecated and will be removed in the future. Configuration templates will be replaced by cluster scripts, see Section 8.1.5, “Using crmsh's Cluster Scripts”.

Configuration templates are ready-made cluster configurations for crmsh. Do not confuse them with the resource templates (as described in Section 8.4.3, “Creating Resource Templates”). Those are templates for the cluster and not for the crm shell.

Configuration templates require minimum effort to be tailored to the particular user's needs. Whenever a template creates a configuration, warning messages give hints which can be edited later for further customization.

The following procedure shows how to create a simple yet functional Apache configuration:

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Create a new configuration from a configuration template:

    1. Switch to the template subcommand:

      crm(live)configure# template
    2. List the available configuration templates:

      crm(live)configure template# list templates
      gfs2-base   filesystem  virtual-ip  apache   clvm     ocfs2    gfs2
    3. Decide which configuration template you need. As we need an Apache configuration, we select the apache template and name it g-intranet:

      crm(live)configure template# new g-intranet apache
      INFO: pulling in template apache
      INFO: pulling in template virtual-ip
  3. Define your parameters:

    1. List the configuration you have created:

      crm(live)configure template# list
      g-intranet
    2. Display the minimum required changes that need to be filled out by you:

      crm(live)configure template# show
      ERROR: 23: required parameter ip not set
      ERROR: 61: required parameter id not set
      ERROR: 65: required parameter configfile not set
    3. Invoke your preferred text editor and fill out all lines that have been displayed as errors in Step 3.b:

      crm(live)configure template# edit
  4. Show the configuration and check whether it is valid (bold text depends on the configuration you have entered in Step 3.c):

    crm(live)configure template# show
    primitive virtual-ip ocf:heartbeat:IPaddr \
        params ip="192.168.1.101"
    primitive apache ocf:heartbeat:apache \
        params configfile="/etc/apache2/httpd.conf"
        monitor apache 120s:60s
    group g-intranet \
        apache virtual-ip
  5. Apply the configuration:

    crm(live)configure template# apply
    crm(live)configure# cd ..
    crm(live)configure# show
  6. Submit your changes to the CIB:

    crm(live)configure# commit

It is possible to simplify the commands even more, if you know the details. The above procedure can be summarized with the following command on the shell:

root # crm configure template \
   new g-intranet apache params \
   configfile="/etc/apache2/httpd.conf" ip="192.168.1.101"

If you are inside your internal crm shell, use the following command:

crm(live)configure template# new intranet apache params \
   configfile="/etc/apache2/httpd.conf" ip="192.168.1.101"

However, the previous command only creates its configuration from the configuration template. It does not apply nor commit it to the CIB.

8.1.7 Testing with Shadow Configuration

A shadow configuration is used to test different configuration scenarios. If you have created several shadow configurations, you can test them one by one to see the effects of your changes.

The usual process looks like this:

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Create a new shadow configuration:

    crm(live)configure# cib new myNewConfig
    INFO: myNewConfig shadow CIB created

    If you omit the name of the shadow CIB, a temporary name @tmp@ is created.

  3. If you want to copy the current live configuration into your shadow configuration, use the following command, otherwise skip this step:

    crm(myNewConfig)# cib reset myNewConfig

    The previous command makes it easier to modify any existing resources later.

  4. Make your changes as usual. After you have created the shadow configuration, all changes go there. To save all your changes, use the following command:

    crm(myNewConfig)# commit
  5. If you need the live cluster configuration again, switch back with the following command:

    crm(myNewConfig)configure# cib use live
    crm(live)# 

8.1.8 Debugging Your Configuration Changes

Before loading your configuration changes back into the cluster, it is recommended to review your changes with ptest. The ptest command can show a diagram of actions that will be induced by committing the changes. You need the graphviz package to display the diagrams. The following example is a transcript, adding a monitor operation:

root # crm configure
crm(live)configure# show fence-bob 
primitive fence-bob stonith:apcsmart \
        params hostlist="bob"
crm(live)configure# monitor fence-bob 120m:60s
crm(live)configure# show changed
primitive fence-bob stonith:apcsmart \
        params hostlist="bob" \
        op monitor interval="120m" timeout="60s"
crm(live)configure# ptest
crm(live)configure# commit

8.1.9 Cluster Diagram

To output a cluster diagram, use the command crm configure graph. It displays the current configuration on its current window, therefore requiring X11.

If you prefer Scalable Vector Graphics (SVG), use the following command:

root # crm configure graph dot config.svg svg

8.2 Managing Corosync Configuration

Corosync is the underlying messaging layer for most HA clusters. The corosync subcommand provides commands for editing and managing the Corosync configuration.

For example, to list the status of the cluster, use status:

root # crm corosync status
Printing ring status.
Local node ID 175704363
RING ID 0
        id      = 10.121.9.43
        status  = ring 0 active with no faults
Quorum information
------------------
Date:             Thu May  8 16:41:56 2014
Quorum provider:  corosync_votequorum
Nodes:            2
Node ID:          175704363
Ring ID:          4032
Quorate:          Yes

Votequorum information
----------------------
Expected votes:   2
Highest expected: 2
Total votes:      2
Quorum:           2  
Flags:            Quorate 

Membership information
----------------------
    Nodeid      Votes Name
 175704363          1 alice.example.com (local)
 175704619          1 bob.example.com

The diff command is very helpful: It compares the Corosync configuration on all nodes (if not stated otherwise) and prints the difference between:

root # crm corosync diff
--- bob
+++ alice
@@ -46,2 +46,2 @@
-       expected_votes: 2
-       two_node: 1
+       expected_votes: 1
+       two_node: 0

For more details, see http://crmsh.nongnu.org/crm.8.html#cmdhelp_corosync.

8.3 Configuring Global Cluster Options

Global cluster options control how the cluster behaves when confronted with certain situations. The predefined values can usually be kept. However, to make key functions of your cluster work correctly, you need to adjust the following parameters after basic cluster setup:

Procedure 8.1: Modifying Global Cluster Options With crm
  1. Log in as root and start the crm tool:

    root # crm configure
  2. Use the following commands to set the options for two-node clusters only:

    crm(live)configure# property no-quorum-policy=stop
    crm(live)configure# property stonith-enabled=true
    Important
    Important: No Support Without STONITH

    A cluster without STONITH is not supported.

  3. Show your changes:

    crm(live)configure# show
    property $id="cib-bootstrap-options" \
       dc-version="1.1.1-530add2a3721a0ecccb24660a97dbfdaa3e68f51" \
       cluster-infrastructure="corosync" \
       expected-quorum-votes="2" \
       no-quorum-policy="stop" \
       stonith-enabled="true"
  4. Commit your changes and exit:

    crm(live)configure# commit
    crm(live)configure# exit

8.4 Configuring Cluster Resources

As a cluster administrator, you need to create cluster resources for every resource or application you run on servers in your cluster. Cluster resources can include Web sites, e-mail servers, databases, file systems, virtual machines, and any other server-based applications or services you want to make available to users at all times.

For an overview of resource types you can create, refer to Section 6.3.3, “Types of Resources”.

8.4.1 Loading Cluster Resources from a File

Parts or all of the configuration can be loaded from a local file or a network URL. Three different methods can be definied:

replace

This option replaces the current configuration with the new source configuration.

update

This option tries to import the source configuration. It adds new items or updates existing items to the current configuration.

push

This option imports the content from the source into the current configuration (same as update). However, it removes objects that are not available in the new configuration.

To load the new configuration from the file mycluster-config.txt use the following syntax:

root # crm configure load push mycluster-config.txt

8.4.2 Creating Cluster Resources

There are three types of RAs (Resource Agents) available with the cluster (for background information, see Section 6.3.2, “Supported Resource Agent Classes”). To add a new resource to the cluster, proceed as follows:

  1. Log in as root and start the crm tool:

    root # crm configure
  2. Configure a primitive IP address:

    crm(live)configure# primitive myIP ocf:heartbeat:IPaddr \
         params ip=127.0.0.99 op monitor interval=60s

    The previous command configures a primitive with the name myIP. You need to choose a class (here ocf), provider (heartbeat), and type (IPaddr). Furthermore, this primitive expects other parameters like the IP address. Change the address to your setup.

  3. Display and review the changes you have made:

    crm(live)configure# show
  4. Commit your changes to take effect:

    crm(live)configure# commit

8.4.3 Creating Resource Templates

If you want to create several resources with similar configurations, a resource template simplifies the task. See also Section 6.5.3, “Resource Templates and Constraints” for some basic background information. Do not confuse them with the normal templates from Section 8.1.6, “Using Configuration Templates”. Use the rsc_template command to get familiar with the syntax:

root # crm configure rsc_template
usage: rsc_template <name> [<class>:[<provider>:]]<type>
        [params <param>=<value> [<param>=<value>...]]
        [meta <attribute>=<value> [<attribute>=<value>...]]
        [utilization <attribute>=<value> [<attribute>=<value>...]]
        [operations id_spec
            [op op_type [<attribute>=<value>...] ...]]

For example, the following command creates a new resource template with the name BigVM derived from the ocf:heartbeat:Xen resource and some default values and operations:

crm(live)configure# rsc_template BigVM ocf:heartbeat:Xen \
   params allow_mem_management="true" \
   op monitor timeout=60s interval=15s \
   op stop timeout=10m \
   op start timeout=10m

Once you defined the new resource template, you can use it in primitives or reference it in order, colocation, or rsc_ticket constraints. To reference the resource template, use the @ sign:

crm(live)configure# primitive MyVM1 @BigVM \
   params xmfile="/etc/xen/shared-vm/MyVM1" name="MyVM1"

The new primitive MyVM1 is going to inherit everything from the BigVM resource templates. For example, the equivalent of the above two would be:

crm(live)configure# primitive MyVM1 ocf:heartbeat:Xen \
   params xmfile="/etc/xen/shared-vm/MyVM1" name="MyVM1" \
   params allow_mem_management="true" \
   op monitor timeout=60s interval=15s \
   op stop timeout=10m \
   op start timeout=10m

If you want to overwrite some options or operations, add them to your (primitive) definition. For instance, the following new primitive MyVM2 doubles the timeout for monitor operations but leaves others untouched:

crm(live)configure# primitive MyVM2 @BigVM \
   params xmfile="/etc/xen/shared-vm/MyVM2" name="MyVM2" \
   op monitor timeout=120s interval=30s

A resource template may be referenced in constraints to stand for all primitives which are derived from that template. This helps to produce a more concise and clear cluster configuration. Resource template references are allowed in all constraints except location constraints. Colocation constraints may not contain more than one template reference.

8.4.4 Creating a STONITH Resource

From the crm perspective, a STONITH device is just another resource. To create a STONITH resource, proceed as follows:

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Get a list of all STONITH types with the following command:

    crm(live)# ra list stonith
    apcmaster                  apcmastersnmp              apcsmart
    baytech                    bladehpi                   cyclades
    drac3                      external/drac5             external/dracmc-telnet
    external/hetzner           external/hmchttp           external/ibmrsa
    external/ibmrsa-telnet     external/ipmi              external/ippower9258
    external/kdumpcheck        external/libvirt           external/nut
    external/rackpdu           external/riloe             external/sbd
    external/vcenter           external/vmware            external/xen0
    external/xen0-ha           fence_legacy               ibmhmc
    ipmilan                    meatware                   nw_rpc100s
    rcd_serial                 rps10                      suicide
    wti_mpc                    wti_nps
  3. Choose a STONITH type from the above list and view the list of possible options. Use the following command:

    crm(live)# ra info stonith:external/ipmi
    IPMI STONITH external device (stonith:external/ipmi)
    
    ipmitool based power management. Apparently, the power off
    method of ipmitool is intercepted by ACPI which then makes
    a regular shutdown. If case of a split brain on a two-node
    it may happen that no node survives. For two-node clusters
    use only the reset method.
    
    Parameters (* denotes required, [] the default):
    
    hostname (string): Hostname
        The name of the host to be managed by this STONITH device.
    ...
  4. Create the STONITH resource with the stonith class, the type you have chosen in Step 3, and the respective parameters if needed, for example:

    crm(live)# configure
    crm(live)configure# primitive my-stonith stonith:external/ipmi \
        params hostname="alice" \
        ipaddr="192.168.1.221" \
        userid="admin" passwd="secret" \
        op monitor interval=60m timeout=120s

8.4.5 Configuring Resource Constraints

Having all the resources configured is only one part of the job. Even if the cluster knows all needed resources, it might still not be able to handle them correctly. For example, try not to mount the file system on the slave node of DRBD (in fact, this would fail with DRBD). Define constraints to make these kind of information available to the cluster.

For more information about constraints, see Section 6.5, “Resource Constraints”.

8.4.5.1 Locational Constraints

The location command defines on which nodes a resource may be run, may not be run or is preferred to be run.

This type of constraint may be added multiple times for each resource. All location constraints are evaluated for a given resource. A simple example that expresses a preference to run the resource fs1 on the node with the name alice to 100 would be the following:

crm(live)configure# location loc-fs1 fs1 100: alice

Another example is a location with pingd:

crm(live)configure# primitive pingd pingd \
    params name=pingd dampen=5s multiplier=100 host_list="r1 r2"
crm(live)configure# location loc-node_pref internal_www \
    rule 50: #uname eq alice \
    rule pingd: defined pingd

Another use case for location constraints are grouping primitives as a resource set. This can be useful if several resources depend on, for example, a ping attribute for network connectivity. In former times, the -inf/ping rules needed to be duplicated several times in the configuration, making it unnecessarily complex.

The following example creates a resource set loc-alice, referencing the virtual IP addresses vip1 and vip2:

crm(live)configure# primitive vip1 ocf:heartbeat:IPaddr2 params ip=192.168.1.5
crm(live)configure# primitive vip2 ocf:heartbeat:IPaddr2 params ip=192.168.1.6
crm(live)configure# location loc-alice { vip1 vip2 } inf: alice

In some cases it is much more efficient and convenient to use resource patterns for your location command. A resource pattern is a regular expression between two slashes. For example, the above virtual IP addresses can be all matched with the following:

crm(live)configure# location  loc-alice /vip.*/ inf: alice

8.4.5.2 Colocational Constraints

The colocation command is used to define what resources should run on the same or on different hosts.

It is only possible to set a score of either +inf or -inf, defining resources that must always or must never run on the same node. It is also possible to use non-infinite scores. In that case the colocation is called advisory and the cluster may decide not to follow them in favor of not stopping other resources if there is a conflict.

For example, to run the resources with the IDs filesystem_resource and nfs_group always on the same host, use the following constraint:

crm(live)configure# colocation nfs_on_filesystem inf: nfs_group filesystem_resource

For a master slave configuration, it is necessary to know if the current node is a master in addition to running the resource locally.

8.4.5.3 Collocating Sets for Resources Without Dependency

Sometimes it is useful to be able to place a group of resources on the same node (defining a colocation constraint), but without having hard dependencies between the resources.

Use the command weak-bond if you want to place resources on the same node, but without any action if one of them fails.

root # crm configure assist weak-bond RES1 RES2

The implementation of weak-bond creates a dummy resource and a colocation constraint with the given resources automatically.

8.4.5.4 Ordering Constraints

The order command defines a sequence of action.

Sometimes it is necessary to provide an order of resource actions or operations. For example, you cannot mount a file system before the device is available to a system. Ordering constraints can be used to start or stop a service right before or after a different resource meets a special condition, such as being started, stopped, or promoted to master.

Use the following command in the crm shell to configure an ordering constraint:

crm(live)configure# order nfs_after_filesystem mandatory: filesystem_resource nfs_group

8.4.5.5 Constraints for the Example Configuration

The example used for this section would not work without additional constraints. It is essential that all resources run on the same machine as the master of the DRBD resource. The DRBD resource must be master before any other resource starts. Trying to mount the DRBD device when it is not the master simply fails. The following constraints must be fulfilled:

  • The file system must always be on the same node as the master of the DRBD resource.

    crm(live)configure# colocation filesystem_on_master inf: \
        filesystem_resource drbd_resource:Master
  • The NFS server and the IP address must be on the same node as the file system.

    crm(live)configure# colocation nfs_with_fs inf: \
       nfs_group filesystem_resource
  • The NFS server and the IP address start after the file system is mounted:

    crm(live)configure# order nfs_second mandatory: \
       filesystem_resource:start nfs_group
  • The file system must be mounted on a node after the DRBD resource is promoted to master on this node.

    crm(live)configure# order drbd_first inf: \
        drbd_resource:promote filesystem_resource:start

8.4.6 Specifying Resource Failover Nodes

To determine a resource failover, use the meta attribute migration-threshold. In case failcount exceeds migration-threshold on all nodes, the resource will remain stopped. For example:

crm(live)configure# location rsc1-alice rsc1 100: alice

Normally, rsc1 prefers to run on alice. If it fails there, migration-threshold is checked and compared to the failcount. If failcount >= migration-threshold then it is migrated to the node with the next best preference.

Start failures set the failcount to inf depend on the start-failure-is-fatal option. Stop failures cause fencing. If there is no STONITH defined, the resource will not migrate.

For an overview, refer to Section 6.5.4, “Failover Nodes”.

8.4.7 Specifying Resource Failback Nodes (Resource Stickiness)

A resource might fail back to its original node when that node is back online and in the cluster. To prevent a resource from failing back to the node that it was running on, or to specify a different node for the resource to fail back to, change its resource stickiness value. You can either specify resource stickiness when you are creating a resource or afterward.

For an overview, refer to Section 6.5.5, “Failback Nodes”.

8.4.8 Configuring Placement of Resources Based on Load Impact

Some resources may have specific capacity requirements such as minimum amount of memory. Otherwise, they may fail to start completely or run with degraded performance.

To take this into account, the High Availability Extension allows you to specify the following parameters:

  1. The capacity a certain node provides.

  2. The capacity a certain resource requires.

  3. An overall strategy for placement of resources.

For detailed background information about the parameters and a configuration example, refer to Section 6.5.6, “Placing Resources Based on Their Load Impact”.

To configure the resource's requirements and the capacity a node provides, use utilization attributes. You can name the utilization attributes according to your preferences and define as many name/value pairs as your configuration needs. In certain cases, some agents update the utilization themselves, for example the VirtualDomain.

In the following example, we assume that you already have a basic configuration of cluster nodes and resources. You now additionally want to configure the capacities a certain node provides and the capacity a certain resource requires.

Procedure 8.2: Adding Or Modifying Utilization Attributes With crm
  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. To specify the capacity a node provides, use the following command and replace the placeholder NODE_1 with the name of your node:

    crm(live)configure# node
    NODE_1 utilization memory=16384 cpu=8

    With these values, NODE_1 would be assumed to provide 16GB of memory and 8 CPU cores to resources.

  3. To specify the capacity a resource requires, use:

    crm(live)configure# primitive xen1 ocf:heartbeat:Xen ... \
         utilization memory=4096 cpu=4

    This would make the resource consume 4096 of those memory units from NODE_1, and 4 of the CPU units.

  4. Configure the placement strategy with the property command:

    crm(live)configure# property ...

    The following values are available:

    default (default value)

    Utilization values are not considered. Resources are allocated according to location scoring. If scores are equal, resources are evenly distributed across nodes.

    utilization

    Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. However, load-balancing is still done based on the number of resources allocated to a node.

    minimal

    Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. An attempt is made to concentrate the resources on as few nodes as possible (to achieve power savings on the remaining nodes).

    balanced

    Utilization values are considered when deciding if a node has enough free capacity to satisfy a resource's requirements. An attempt is made to distribute the resources evenly, thus optimizing resource performance.

    Note
    Note: Configuring Resource Priorities

    The available placement strategies are best-effort—they do not yet use complex heuristic solvers to always reach optimum allocation results. Ensure that resource priorities are properly set so that your most important resources are scheduled first.

  5. Commit your changes before leaving crmsh:

    crm(live)configure# commit

The following example demonstrates a three node cluster of equal nodes, with 4 virtual machines:

crm(live)configure# node alice utilization memory="4000"
crm(live)configure# node bob utilization memory="4000"
crm(live)configure# node charlie utilization memory="4000"
crm(live)configure# primitive xenA ocf:heartbeat:Xen \
    utilization hv_memory="3500" meta priority="10" \
    params xmfile="/etc/xen/shared-vm/vm1"
crm(live)configure# primitive xenB ocf:heartbeat:Xen \
    utilization hv_memory="2000" meta priority="1" \
    params xmfile="/etc/xen/shared-vm/vm2"
crm(live)configure# primitive xenC ocf:heartbeat:Xen \
    utilization hv_memory="2000" meta priority="1" \
    params xmfile="/etc/xen/shared-vm/vm3"
crm(live)configure# primitive xenD ocf:heartbeat:Xen \
    utilization hv_memory="1000" meta priority="5" \
    params xmfile="/etc/xen/shared-vm/vm4"
crm(live)configure# property placement-strategy="minimal"

With all three nodes up, xenA will be placed onto a node first, followed by xenD. xenB and xenC would either be allocated together or one of them with xenD.

If one node failed, too little total memory would be available to host them all. xenA would be ensured to be allocated, as would xenD. However, only one of xenB or xenC could still be placed, and since their priority is equal, the result is not defined yet. To resolve this ambiguity as well, you would need to set a higher priority for either one.

8.4.9 Configuring Resource Monitoring

To monitor a resource, there are two possibilities: either define a monitor operation with the op keyword or use the monitor command. The following example configures an Apache resource and monitors it every 60 seconds with the op keyword:

crm(live)configure# primitive apache apache \
  params ... \
  op monitor interval=60s timeout=30s

The same can be done with:

crm(live)configure# primitive apache apache \
   params ...
crm(live)configure# monitor apache 60s:30s

For an overview, refer to Section 6.4, “Resource Monitoring”.

8.4.10 Configuring a Cluster Resource Group

One of the most common elements of a cluster is a set of resources that needs to be located together. Start sequentially and stop in the reverse order. To simplify this configuration we support the concept of groups. The following example creates two primitives (an IP address and an e-mail resource):

  1. Run the crm command as system administrator. The prompt changes to crm(live).

  2. Configure the primitives:

    crm(live)# configure
    crm(live)configure# primitive Public-IP ocf:heartbeat:IPaddr \
       params ip=1.2.3.4 id= Public-IP
    crm(live)configure# primitive Email systemd:postfix \
       params id=Email
  3. Group the primitives with their relevant identifiers in the correct order:

    crm(live)configure# group g-mailsvc Public-IP Email

To change the order of a group member, use the modgroup command from the configure subcommand. Use the following commands to move the primitive Email before Public-IP. (This is just to demonstrate the feature):

crm(live)configure# modgroup g-mailsvc add Email before Public-IP

In case you want to remove a resource from a group (for example, Email), use this command:

crm(live)configure# modgroup g-mailsvc remove Email

For an overview, refer to Section 6.3.5.1, “Groups”.

8.4.11 Configuring a Clone Resource

Clones were initially conceived as a convenient way to start N instances of an IP resource and have them distributed throughout the cluster for load balancing. They have turned out to be useful for several other purposes, including integrating with DLM, the fencing subsystem and OCFS2. You can clone any resource, provided the resource agent supports it.

Learn more about cloned resources in Section 6.3.5.2, “Clones”.

8.4.11.1 Creating Anonymous Clone Resources

To create an anonymous clone resource, first create a primitive resource and then refer to it with the clone command. Do the following:

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Configure the primitive, for example:

    crm(live)configure# primitive Apache ocf:heartbeat:apache
  3. Clone the primitive:

    crm(live)configure# clone cl-apache Apache

8.4.11.2 Creating Stateful/Multi-State Clone Resources

Multi-state resources are a specialization of clones. This type allows the instances to be in one of two operating modes, be it active/passive, primary/secondary, or master/slave.

To create a stateful clone resource, first create a primitive resource and then the multi-state resource. The multi-state resource must support at least promote and demote operations.

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Configure the primitive. Change the intervals if needed:

    crm(live)configure# primitive my-rsc ocf:myCorp:myAppl \
        op monitor interval=60 \
        op monitor interval=61 role=Master
  3. Create the multi-state resource:

    crm(live)configure# ms ms-rsc my-rsc

8.5 Managing Cluster Resources

Apart from the possibility to configure your cluster resources, the crm tool also allows you to manage existing resources. The following subsections gives you an overview.

8.5.1 Showing Cluster Resources

When administering a cluster the command crm configure show lists the current CIB objects like cluster configuration, global options, primitives, and others:

root # crm configure show
node 178326192: alice
node 178326448: bob
primitive admin_addr IPaddr2 \
        params ip=192.168.2.1 \
        op monitor interval=10 timeout=20
primitive stonith-sbd stonith:external/sbd \
        params pcmk_delay_max=30
property cib-bootstrap-options: \
        have-watchdog=true \
        dc-version=1.1.15-17.1-e174ec8 \
        cluster-infrastructure=corosync \
        cluster-name=hacluster \
        stonith-enabled=true \
        placement-strategy=balanced \
        standby-mode=true
rsc_defaults rsc-options: \
        resource-stickiness=1 \
        migration-threshold=3
op_defaults op-options: \
        timeout=600 \
        record-pending=true

In case you have lots of resources, the output of show is too verbose. To restrict the output, use the name of the resource. For example, to list the properties of the primitive admin_addr only, append the resource name to show:

root # crm configure show admin_addr
primitive admin_addr IPaddr2 \
        params ip=192.168.2.1 \
        op monitor interval=10 timeout=20

However, in some cases, you want to limit the output of specific resources even more. This can be achieved with filters. Filters limit the output to specific components. For example, to list the nodes only, use type:node:

root # crm configure show type:node
node 178326192: alice
node 178326448: bob

In case you are also interested in primitives, use the or operator:

root # crm configure show type:node or type:primitive
node 178326192: alice
node 178326448: bob
primitive admin_addr IPaddr2 \
        params ip=192.168.2.1 \
        op monitor interval=10 timeout=20
primitive stonith-sbd stonith:external/sbd \
        params pcmk_delay_max=30

Furthermore, to search for an object that starts with a certain string, use this notation:

root # crm configure show type:primitive and and 'admin*'
primitive admin_addr IPaddr2 \
        params ip=192.168.2.1 \
        op monitor interval=10 timeout=20

To list all available types, enter crm configure show type: and press the →| key. The bash completion will give you a list of all types.

8.5.2 Starting a New Cluster Resource

To start a new cluster resource you need the respective identifier. Proceed as follows:

  1. Log in as root and start the crm interactive shell:

    root # crm
  2. Switch to the resource level:

    crm(live)# resource
  3. Start the resource with start and press the →| key to show all known resources:

    crm(live)resource# start ID

8.5.3 Cleaning Up Resources

A resource will be automatically restarted if it fails, but each failure raises the resource's failcount. If a migration-threshold has been set for that resource, the node will no longer be allowed to run the resource as soon as the number of failures has reached the migration threshold.

  1. Open a shell and log in as user root.

  2. Get a list of all your resources:

    root # crm resource list
      ...
    Resource Group: dlm-clvm:1
             dlm:1  (ocf:pacemaker:controld) Started
             clvm:1 (ocf:heartbeat:clvm) Started
  3. To clean up the resource dlm, for example:

    root # crm resource cleanup dlm

8.5.4 Removing a Cluster Resource

Proceed as follows to remove a cluster resource:

  1. Log in as root and start the crm interactive shell:

    root # crm configure
  2. Run the following command to get a list of your resources:

    crm(live)# resource status

    For example, the output can look like this (whereas myIP is the relevant identifier of your resource):

    myIP    (ocf:IPaddr:heartbeat) ...
  3. Delete the resource with the relevant identifier (which implies a commit too):

    crm(live)# configure delete YOUR_ID
  4. Commit the changes:

    crm(live)# configure commit

8.5.5 Migrating a Cluster Resource

Although resources are configured to automatically fail over (or migrate) to other nodes of the cluster if a hardware or software failure occurs, you can also manually move a resource to another node using either Hawk2 or the command line.

Use the migrate command for this task. For example, to migrate the resource ipaddress1 to a cluster node named bob, use these commands:

root # crm resource
crm(live)resource# migrate ipaddress1 bob

8.5.6 Grouping/Tagging Resources

Tags are a way to refer to multiple resources at once, without creating any colocation or ordering relationship between them. This can be useful for grouping conceptually related resources. For example, if you have several resources related to a database, create a tag called databases and add all resources related to the database to this tag:

root # crm configure databases: db1 db2 db3

This allows you to start them all with a single command:

root # crm resource start databases

Similarly, you can stop them all too:

root # crm resource stop databases

8.5.7 Getting Health Status

The health status of a cluster or node can be displayed with so called scripts. A script can perform different tasks—they are not targeted to health. However, for this subsection, we focus on how to get the health status.

To get all the details about the health command, use describe:

root # crm script describe health

It shows a description and a list of all parameters and their default values. To execute a script, use run:

root # crm script run health

If you prefer to run only one step from the suite, the describe command lists all available steps in the Steps category.

For example, the following command executes the first step of the health command. The output is stored in the health.json file for further investigation:

root # crm script run health
    statefile='health.json'

It is also possible to run the above commands with crm cluster health.

For additional information regarding scripts, see http://crmsh.github.io/scripts/.

8.6 Setting Passwords Independent of cib.xml

In case your cluster configuration contains sensitive information, such as passwords, it should be stored in local files. That way, these parameters will never be logged or leaked in support reports.

Before using secret, better run the show command first to get an overview of all your resources:

root # crm configure show
primitive mydb ocf:heartbeat:mysql \
   params replication_user=admin ...

If you want to set a password for the above mydb resource, use the following commands:

root # crm resource secret mydb set passwd linux
INFO: syncing /var/lib/heartbeat/lrm/secrets/mydb/passwd to [your node list]

You can get the saved password back with:

root # crm resource secret mydb show passwd
linux

Note that the parameters need to be synchronized between nodes; the crm resource secret command will take care of that. We highly recommend to only use this command to manage secret parameters.

8.7 Retrieving History Information

Investigating the cluster history is a complex task. To simplify this task, crmsh contains the history command with its subcommands. It is assumed SSH is configured correctly.

Each cluster moves states, migrates resources, or starts important processes. All these actions can be retrieved by subcommands of history.

By default, all history commands look at the events of the last hour. To change this time frame, use the limit subcommand. The syntax is:

root # crm history
crm(live)history# limit FROM_TIME [TO_TIME]

Some valid examples include:

limit4:00pm , limit16:00

Both commands mean the same, today at 4pm.

limit2012/01/12 6pm

January 12th 2012 at 6pm

limit"Sun 5 20:46"

In the current year of the current month at Sunday the 5th at 8:46pm

Find more examples and how to create time frames at http://labix.org/python-dateutil.

The info subcommand shows all the parameters which are covered by the crm report:

crm(live)history# info
Source: live
Period: 2012-01-12 14:10:56 - end
Nodes: alice
Groups: 
Resources:

To limit crm report to certain parameters view the available options with the subcommand help.

To narrow down the level of detail, use the subcommand detail with a level:

crm(live)history# detail 1

The higher the number, the more detailed your report will be. Default is 0 (zero).

After you have set above parameters, use log to show the log messages.

To display the last transition, use the following command:

crm(live)history# transition -1
INFO: fetching new logs, please wait ...

This command fetches the logs and runs dotty (from the graphviz package) to show the transition graph. The shell opens the log file which you can browse with the and cursor keys.

If you do not want to open the transition graph, use the nograph option:

crm(live)history# transition -1 nograph

8.8 For More Information

  • The crm man page.

  • Visit the upstream project documentation at http://crmsh.github.io/documentation.

  • See Article “Highly Available NFS Storage with DRBD and Pacemaker” for an exhaustive example.

9 Adding or Modifying Resource Agents

Abstract

All tasks that need to be managed by a cluster must be available as a resource. There are two major groups here to consider: resource agents and STONITH agents. For both categories, you can add your own agents, extending the abilities of the cluster to your own needs.

9.1 STONITH Agents

A cluster sometimes detects that one of the nodes is behaving strangely and needs to remove it. This is called fencing and is commonly done with a STONITH resource.

Warning
Warning: External SSH/STONITH Are Not Supported

It is impossible to know how SSH might react to other system problems. For this reason, external SSH/STONITH agents (like stonith:external/ssh) are not supported for production environments. If you still want to use such agents for testing, install the libglue-devel package.

To get a list of all currently available STONITH devices (from the software side), use the command crm ra list stonith. If you do not find your favorite agent, install the -devel package. For more information on STONITH devices and resource agents, see Chapter 10, Fencing and STONITH.

As of yet there is no documentation about writing STONITH agents. If you want to write new STONITH agents, consult the examples available in the source of the cluster-glue package.

9.2 Writing OCF Resource Agents

All OCF resource agents (RAs) are available in /usr/lib/ocf/resource.d/, see Section 6.3.2, “Supported Resource Agent Classes” for more information. Each resource agent must supported the following operations to control it:

start

start or enable the resource

stop

stop or disable the resource

status

returns the status of the resource

monitor

similar to status, but checks also for unexpected states

validate

validate the resource's configuration

meta-data

returns information about the resource agent in XML

The general procedure of how to create an OCF RA is like the following:

  1. Load the file /usr/lib/ocf/resource.d/pacemaker/Dummy as a template.

  2. Create a new subdirectory for each new resource agents to avoid naming contradictions. For example, if you have a resource group kitchen with the resource coffee_machine, add this resource to the directory /usr/lib/ocf/resource.d/kitchen/. To access this RA, execute the command crm:

    root # crm configure primitive coffee_1 ocf:coffee_machine:kitchen ...
  3. Implement the different shell functions and save your file under a different name.

More details about writing OCF resource agents can be found at http://linux-ha.org/wiki/Resource_Agents. Find special information about several concepts at Chapter 1, Product Overview.

9.3 OCF Return Codes and Failure Recovery

According to the OCF specification, there are strict definitions of the exit codes an action must return. The cluster always checks the return code against the expected result. If the result does not match the expected value, then the operation is considered to have failed and a recovery action is initiated. There are three types of failure recovery:

Table 9.1: Failure Recovery Types

Recovery Type

Description

Action Taken by the Cluster

soft

A transient error occurred.

Restart the resource or move it to a new location.

hard

A non-transient error occurred. The error may be specific to the current node.

Move the resource elsewhere and prevent it from being retried on the current node.

fatal

A non-transient error occurred that will be common to all cluster nodes. This means a bad configuration was specified.

Stop the resource and prevent it from being started on any cluster node.

Assuming an action is considered to have failed, the following table outlines the different OCF return codes. It also shows the type of recovery the cluster will initiate when the respective error code is received.

Table 9.2: OCF Return Codes

OCF Return Code

OCF Alias

Description

Recovery Type

0

OCF_SUCCESS

Success. The command completed successfully. This is the expected result for all start, stop, promote and demote commands.

soft

1

OCF_ERR_­GENERIC

Generic there was a problem error code.

soft

2

OCF_ERR_ARGS

The resource’s configuration is not valid on this machine (for example, it refers to a location/tool not found on the node).

hard

3

OCF_­ERR_­UN­IMPLEMENTED

The requested action is not implemented.

hard

4

OCF_ERR_PERM

The resource agent does not have sufficient privileges to complete the task.

hard

5

OCF_ERR_­INSTALLED

The tools required by the resource are not installed on this machine.

hard

6

OCF_ERR_­CONFIGURED

The resource’s configuration is invalid (for example, required parameters are missing).

fatal

7

OCF_NOT_­RUNNING

The resource is not running. The cluster will not attempt to stop a resource that returns this for any action.

This OCF return code may or may not require resource recovery—it depends on what is the expected resource status. If unexpected, then soft recovery.

N/A

8

OCF_RUNNING_­MASTER

The resource is running in Master mode.

soft

9

OCF_FAILED_­MASTER

The resource is in Master mode but has failed. The resource will be demoted, stopped and then started (and possibly promoted) again.

soft

other

N/A

Custom error code.

soft

10 Fencing and STONITH

Abstract

Fencing is a very important concept in computer clusters for HA (High Availability). A cluster sometimes detects that one of the nodes is behaving strangely and needs to remove it. This is called fencing and is commonly done with a STONITH resource. Fencing may be defined as a method to bring an HA cluster to a known state.

Every resource in a cluster has a state attached. For example: resource r1 is started on alice. In an HA cluster, such a state implies that resource r1 is stopped on all nodes except alice, because the cluster must make sure that every resource may be started on only one node. Every node must report every change that happens to a resource. The cluster state is thus a collection of resource states and node states.

When the state of a node or resource cannot be established with certainty, fencing comes in. Even when the cluster is not aware of what is happening on a given node, fencing can ensure that the node does not run any important resources.

10.1 Classes of Fencing

There are two classes of fencing: resource level and node level fencing. The latter is the primary subject of this chapter.

Resource Level Fencing

Resource level fencing ensures exclusive access to a given resource. Common examples of this are changing the zoning of the node from a SAN fiber channel switch (thus locking the node out of access to its disks) or methods like SCSI reserve. For examples, refer to Section 11.10, “Additional Mechanisms for Storage Protection”.

Node Level Fencing

Node level fencing prevents a failed node from accessing shared resources entirely. This is usually done in a simple and abrupt way: reset or power off the node.

10.2 Node Level Fencing

In a Pacemaker cluster, the implementation of node level fencing is STONITH (Shoot The Other Node in the Head). The High Availability Extension includes the stonith command line tool, an extensible interface for remotely powering down a node in the cluster. For an overview of the available options, run stonith --help or refer to the man page of stonith for more information.

10.2.1 STONITH Devices

To use node level fencing, you first need to have a fencing device. To get a list of STONITH devices which are supported by the High Availability Extension, run one of the following commands on any of the nodes:

root # stonith -L

or

root # crm ra list stonith

STONITH devices may be classified into the following categories:

Power Distribution Units (PDU)

Power Distribution Units are an essential element in managing power capacity and functionality for critical network, server and data center equipment. They can provide remote load monitoring of connected equipment and individual outlet power control for remote power recycling.

Uninterruptible Power Supplies (UPS)

A stable power supply provides emergency power to connected equipment by supplying power from a separate source if a utility power failure occurs.

Blade Power Control Devices

If you are running a cluster on a set of blades, then the power control device in the blade enclosure is the only candidate for fencing. Of course, this device must be capable of managing single blade computers.

Lights-out Devices

Lights-out devices (IBM RSA, HP iLO, Dell DRAC) are becoming increasingly popular and may even become standard in off-the-shelf computers. However, they are inferior to UPS devices, because they share a power supply with their host (a cluster node). If a node stays without power, the device supposed to control it would be useless. In that case, the CRM would continue its attempts to fence the node indefinitely while all other resource operations would wait for the fencing/STONITH operation to complete.

Testing Devices

Testing devices are used exclusively for testing purposes. They are usually more gentle on the hardware. Before the cluster goes into production, they must be replaced with real fencing devices.

The choice of the STONITH device depends mainly on your budget and the kind of hardware you use.

10.2.2 STONITH Implementation

The STONITH implementation of SUSE® Linux Enterprise High Availability Extension consists of two components:

stonithd

stonithd is a daemon which can be accessed by local processes or over the network. It accepts the commands which correspond to fencing operations: reset, power-off, and power-on. It can also check the status of the fencing device.

The stonithd daemon runs on every node in the CRM HA cluster. The stonithd instance running on the DC node receives a fencing request from the CRM. It is up to this and other stonithd programs to carry out the desired fencing operation.

STONITH Plug-ins

For every supported fencing device there is a STONITH plug-in which is capable of controlling said device. A STONITH plug-in is the interface to the fencing device. The STONITH plug-ins contained in the cluster-glue package reside in /usr/lib64/stonith/plugins on each node. (If you installed the fence-agents package, too, the plug-ins contained there are installed in /usr/sbin/fence_*.) All STONITH plug-ins look the same to stonithd, but are quite different on the other side reflecting the nature of the fencing device.

Some plug-ins support more than one device. A typical example is ipmilan (or external/ipmi) which implements the IPMI protocol and can control any device which supports this protocol.

10.3 STONITH Resources and Configuration

To set up fencing, you need to configure one or more STONITH resources—the stonithd daemon requires no configuration. All configuration is stored in the CIB. A STONITH resource is a resource of class stonith (see Section 6.3.2, “Supported Resource Agent Classes”). STONITH resources are a representation of STONITH plug-ins in the CIB. Apart from the fencing operations, the STONITH resources can be started, stopped and monitored, like any other resource. Starting or stopping STONITH resources means loading and unloading the STONITH device driver on a node. Starting and stopping are thus only administrative operations and do not translate to any operation on the fencing device itself. However, monitoring does translate to logging it to the device (to verify that the device will work in case it is needed). When a STONITH resource fails over to another node it enables the current node to talk to the STONITH device by loading the respective driver.

STONITH resources can be configured like any other resource. For details how to do so with your preferred cluster management tool:

The list of parameters (attributes) depends on the respective STONITH type. To view a list of parameters for a specific device, use the stonith command:

stonith -t stonith-device-type -n

For example, to view the parameters for the ibmhmc device type, enter the following:

stonith -t ibmhmc -n

To get a short help text for the device, use the -h option:

stonith -t stonith-device-type -h

10.3.1 Example STONITH Resource Configurations

In the following, find some example configurations written in the syntax of the crm command line tool. To apply them, put the sample in a text file (for example, sample.txt) and run:

root # crm < sample.txt

For more information about configuring resources with the crm command line tool, refer to Chapter 8, Configuring and Managing Cluster Resources (Command Line).

Example 10.1: Configuration of an IBM RSA Lights-out Device

An IBM RSA lights-out device might be configured like this:

configure
primitive st-ibmrsa-1 stonith:external/ibmrsa-telnet \
params nodename=alice ip_address=192.168.0.101 \
username=USERNAME password=PASSW0RD
primitive st-ibmrsa-2 stonith:external/ibmrsa-telnet \
params nodename=bob ip_address=192.168.0.102 \
username=USERNAME password=PASSW0RD
location l-st-alice st-ibmrsa-1 -inf: alice
location l-st-bob st-ibmrsa-2 -inf: bob
commit

In this example, location constraints are used for the following reason: There is always a certain probability that the STONITH operation is going to fail. Therefore, a STONITH operation on the node which is the executioner as well is not reliable. If the node is reset, it cannot send the notification about the fencing operation outcome. The only way to do that is to assume that the operation is going to succeed and send the notification beforehand. But if the operation fails, problems could arise. Therefore, by convention, stonithd refuses to terminate its host.

Example 10.2: Configuration of a UPS Fencing Device

The configuration of a UPS type fencing device is similar to the examples above. The details are not covered here. All UPS devices employ the same mechanics for fencing. How the device is accessed varies. Old UPS devices only had a serial port, usually connected at 1200baud using a special serial cable. Many new ones still have a serial port, but often they also use a USB or Ethernet interface. The kind of connection you can use depends on what the plug-in supports.

For example, compare the apcmaster with the apcsmart device by using the stonith -t stonith-device-type -n command:

stonith -t apcmaster -h

returns the following information:

STONITH Device: apcmaster - APC MasterSwitch (via telnet)
NOTE: The APC MasterSwitch accepts only one (telnet)
connection/session a time. When one session is active,
subsequent attempts to connect to the MasterSwitch will fail.
For more information see http://www.apc.com/
List of valid parameter names for apcmaster STONITH device:
ipaddr
login
 password

With

stonith -t apcsmart -h

you get the following output:

STONITH Device: apcsmart - APC Smart UPS
(via serial port - NOT USB!). 
Works with higher-end APC UPSes, like
Back-UPS Pro, Smart-UPS, Matrix-UPS, etc.
(Smart-UPS may have to be >= Smart-UPS 700?).
See http://www.networkupstools.org/protocols/apcsmart.html
for protocol compatibility details.
For more information see http://www.apc.com/
List of valid parameter names for apcsmart STONITH device:
ttydev
hostlist

The first plug-in supports APC UPS with a network port and telnet protocol. The second plug-in uses the APC SMART protocol over the serial line, which is supported by many different APC UPS product lines.

Example 10.3: Configuration of a Kdump Device

Kdump belongs to the Special Fencing Devices and is in fact the opposite of a fencing device. The plug-in checks if a Kernel dump is in progress on a node. If so, it returns true, and acts as if the node has been fenced.

Use the stonith:fence_kdump resource agent (provided by the package fence-agents) to monitor all nodes with the Kdump function enabled. Find a configuration example for the resource below:

configure
  primitive st-kdump stonith:fence_kdump \
  params nodename="alice "\ 1
  pcmk_host_check="static-list" \
  pcmk_reboot_action="off" \
  pcmk_monitor_action="metadata" \
  pcmk_reboot_retries="1" \
  timeout="60"
  commit

1

Name of the node to be monitored. If you need to monitor more than one node, configure more STONITH resources. To prevent a specific node from using a fencing device, add location constraints.

The fencing action will be started after the timeout of the resource.

In /etc/sysconfig/kdump on each node, configure KDUMP_POSTSCRIPT to send a notification to all nodes when the Kdump process is finished. For example:

/usr/lib64/fence_kdump_send -i INTERVAL -p PORT -c 1 alice bob charlie [...]

The node that does a Kdump will restart automatically after Kdump has finished. Do not forget to open a port in the firewall for the fence_kdump resource. The default port is 7410.

The kdump plug-in must be used in concert with another, real STONITH device, for example, external/ipmi. The order of the fencing devices must be specified by crm configure fencing_topology. To achieve that kdump is checked before triggering a real fencing mechanism (like external/ipmi), use a configuration similar to the following:

fencing_topology \
  alice: kdump-node1 ipmi-node1 \
  bob: kdump-node2 ipmi-node2

For more details on fencing_topology:

crm configure help fencing_topology

10.4 Monitoring Fencing Devices

Like any other resource, the STONITH class agents also support the monitoring operation for checking status.

Note
Note: Monitoring STONITH Resources

Monitor STONITH resources regularly, yet sparingly. For most devices a monitoring interval of at least 1800 seconds (30 minutes) should suffice.

Fencing devices are an indispensable part of an HA cluster, but the less you need to use them, the better. Power management equipment is often affected by too much broadcast traffic. Some devices cannot handle more than ten or so connections per minute. Some get confused if two clients try to connect at the same time. Most cannot handle more than one session at a time.

Checking the status of fencing devices once every few hours should usually be enough. The probability that a fencing operation needs to be performed and the power switch fails is low.

For detailed information on how to configure monitor operations, refer to Section 8.4.9, “Configuring Resource Monitoring” for the command line approach.

10.5 Special Fencing Devices

In addition to plug-ins which handle real STONITH devices, there are special purpose STONITH plug-ins.

Warning
Warning: For Testing Only

Some STONITH plug-ins mentioned below are for demonstration and testing purposes only. Do not use any of the following devices in real-life scenarios because this may lead to data corruption and unpredictable results:

  • external/ssh

  • ssh

fence_kdump

This plug-in checks if a Kernel dump is in progress on a node. If so, it returns true, and acts as if the node has been fenced. The node cannot run any resources during the dump anyway. This avoids fencing a node that is already down but doing a dump, which takes some time. The plug-in must be used in concert with another, real STONITH device.

For configuration details, see Example 10.3, “Configuration of a Kdump Device”.

external/sbd

This is a self-fencing device. It reacts to a so-called poison pill which can be inserted into a shared disk. On shared-storage connection loss, it stops the node from operating. Learn how to use this STONITH agent to implement storage-based fencing in Chapter 11, Procedure 11.7, “Configuring the Cluster to Use SBD”. See also http://www.linux-ha.org/wiki/SBD_Fencing for more details.

Important
Important: external/sbd and DRBD

The external/sbd fencing mechanism requires that the SBD partition is readable directly from each node. Thus, a DRBD* device must not be used for an SBD partition.

However, you can use the fencing mechanism for a DRBD cluster, provided the SBD partition is located on a shared disk that is not mirrored or replicated.

external/ssh

Another software-based fencing mechanism. The nodes must be able to log in to each other as root without passwords. It takes a single parameter, hostlist, specifying the nodes that it will target. As it is not able to reset a truly failed node, it must not be used for real-life clusters—for testing and demonstration purposes only. Using it for shared storage would result in data corruption.

meatware

meatware requires help from the user to operate. Whenever invoked, meatware logs a CRIT severity message which shows up on the node's console. The operator then confirms that the node is down and issues a meatclient(8) command. This tells meatware to inform the cluster that the node should be considered dead. See /usr/share/doc/packages/cluster-glue/README.meatware for more information.

suicide

This is a software-only device, which can reboot a node it is running on, using the reboot command. This requires action by the node's operating system and can fail under certain circumstances. Therefore avoid using this device whenever possible. However, it is safe to use on one-node clusters.

Diskless SBD

This configuration is useful if you want a fencing mechanism without shared storage. In this diskless mode, SBD fences nodes by using the hardware watchdog without relying on any shared device. However, diskless SBD cannot handle a split brain scenario for a two-node cluster. Therefore, three or more nodes are required for using diskless SBD.

suicide is the only exception to the I do not shoot my host rule.

10.6 Basic Recommendations

Check the following list of recommendations to avoid common mistakes:

  • Do not configure several power switches in parallel.

  • To test your STONITH devices and their configuration, pull the plug once from each node and verify that fencing the node does takes place.

  • Test your resources under load and verify the timeout values are appropriate. Setting timeout values too low can trigger (unnecessary) fencing operations. For details, refer to Section 6.3.9, “Timeout Values”.

  • Use appropriate fencing devices for your setup. For details, also refer to Section 10.5, “Special Fencing Devices”.

  • Configure one or more STONITH resources. By default, the global cluster option stonith-enabled is set to true. If no STONITH resources have been defined, the cluster will refuse to start any resources.

  • Do not set the global cluster option stonith-enabled to false for the following reasons:

    • Clusters without STONITH enabled are not supported.

    • DLM/OCFS2 will block forever waiting for a fencing operation that will never happen.

  • Do not set the global cluster option startup-fencing to false. By default, it is set to true for the following reason: If a node is in an unknown state during cluster start-up, the node will be fenced once to clarify its status.

10.7 For More Information

/usr/share/doc/packages/cluster-glue

In your installed system, this directory contains README files for many STONITH plug-ins and devices.

http://www.linux-ha.org/wiki/STONITH

Information about STONITH on the home page of the The High Availability Linux Project.

http://www.clusterlabs.org/doc/
  • Pacemaker Explained: Explains the concepts used to configure Pacemaker. Contains comprehensive and very detailed information for reference.

http://techthoughts.typepad.com/managing_computers/2007/10/split-brain-quo.html

Article explaining the concepts of split brain, quorum and fencing in HA clusters.

11 Storage Protection and SBD

Abstract

SBD (STONITH Block Device) provides a node fencing mechanism for Pacemaker-based clusters through the exchange of messages via shared block storage (SAN, iSCSI, FCoE, etc.). This isolates the fencing mechanism from changes in firmware version or dependencies on specific firmware controllers. SBD needs a watchdog on each node to ensure that misbehaving nodes are really stopped. Under certain conditions, it is also possible to use SBD without shared storage, by running it in diskless mode.

The ha-cluster-bootstrap scripts provide an automated way to set up a cluster with the option of using SBD as fencing mechanism. For details, see the Installation and Setup Quick Start. However, manually setting up SBD provides you with more options regarding the individual settings.

This chapter explains the concepts behind SBD. It guides you through configuring the components needed by SBD to protect your cluster from potential data corruption in case of a split brain scenario.

In addition to node level fencing, you can use additional mechanisms for storage protection, such as LVM2 exclusive activation or OCFS2 file locking support (resource level fencing). They protect your system against administrative or application faults.

11.1 Conceptual Overview

SBD expands to Storage-Based Death or STONITH Block Device.

The highest priority of the High Availability cluster stack is to protect the integrity of data. This is achieved by preventing uncoordinated concurrent access to data storage. The cluster stack takes care of this using several control mechanisms.

However, network partitioning or software malfunction could potentially cause scenarios where several DCs are elected in a cluster. If this so-called split brain scenario were allowed to unfold, data corruption might occur.

Node fencing via STONITH is the primary mechanism to prevent this. Using SBD as a node fencing mechanism is one way of shutting down nodes without using an external power off device in case of a split brain scenario.

SBD Components and Mechanisms
SBD Partition

In an environment where all nodes have access to shared storage, a small partition of the device is formatted for use with SBD. The size of the partition depends on the block size of the used disk (for example, 1 MB for standard SCSI disks with 512 Byte block size or 4 MB for DASD disks with 4 kB block size). The initialization process creates a message layout on the device with slots for up to 255 nodes.

SBD Daemon

After the respective SBD daemon is configured, it is brought online on each node before the rest of the cluster stack is started. It is terminated after all other cluster components have been shut down, thus ensuring that cluster resources are never activated without SBD supervision.

Messages

The daemon automatically allocates one of the message slots on the partition to itself, and constantly monitors it for messages addressed to itself. Upon receipt of a message, the daemon immediately complies with the request, such as initiating a power-off or reboot cycle for fencing.

Also, the daemon constantly monitors connectivity to the storage device, and terminates itself in case the partition becomes unreachable. This guarantees that it is not disconnected from fencing messages. If the cluster data resides on the same logical unit in a different partition, this is not an additional point of failure: The workload will terminate anyway if the storage connectivity has been lost.

Watchdog

Whenever SBD is used, a correctly working watchdog is crucial. Modern systems support a hardware watchdog that needs to be tickled or fed by a software component. The software component (in this case, the SBD daemon) feeds the watchdog by regularly writing a service pulse to the watchdog. If the daemon stops feeding the watchdog, the hardware will enforce a system restart. This protects against failures of the SBD process itself, such as dying, or becoming stuck on an IO error.

If Pacemaker integration is activated, SBD will not self-fence if device majority is lost. For example, your cluster contains three nodes: A, B, and C. Because of a network split, A can only see itself while B and C can still communicate. In this case, there are two cluster partitions: one with quorum because of being the majority (B, C), and one without (A). If this happens while the majority of fencing devices are unreachable, node A would immediately commit suicide, but nodes B and C would continue to run.

11.2 Overview of Manually Setting Up SBD

The following steps are necessary to manually set up storage-based protection. They must be executed as root. Before you start, check Section 11.3, “Requirements”.

  1. Setting Up the Watchdog

  2. Depending on your scenario, either use SBD with one to three devices or in diskless mode. For an outline, see Section 11.4, “Number of SBD Devices”. The detailed setup is described in:

  3. Testing SBD and Fencing

11.3 Requirements

  • You can use up to three SBD devices for storage-based fencing. When using one to three devices, the shared storage must be accessible from all nodes.

  • The path to the shared storage device must be persistent and consistent across all nodes in the cluster. Use stable device names such as /dev/disk/by-id/dm-uuid-part1-mpath-abcedf12345.

  • The shared storage can be connected via Fibre Channel (FC), Fibre Channel over Ethernet (FCoE), or even iSCSI.

  • The shared storage segment must not use host-based RAID, LVM2, or DRBD*. DRBD can be split, which is problematic for SBD, as there cannot be two states in SBD. Cluster multi-device (Cluster MD) cannot be used for SBD.

  • However, using storage-based RAID and multipathing is recommended for increased reliability.

  • An SBD device can be shared between different clusters, as long as no more than 255 nodes share the device.

  • For clusters with more than two nodes, you can also use SBD in diskless mode.

11.4 Number of SBD Devices

SBD supports the use of up to three devices:

One Device

The most simple implementation. It is appropriate for clusters where all of your data is on the same shared storage.

Two Devices

This configuration is primarily useful for environments that use host-based mirroring but where no third storage device is available. SBD will not terminate itself if it loses access to one mirror leg, allowing the cluster to continue. However, since SBD does not have enough knowledge to detect an asymmetric split of the storage, it will not fence the other side while only one mirror leg is available. Thus, it cannot automatically tolerate a second failure while one of the storage arrays is down.

Three Devices

The most reliable configuration. It is resilient against outages of one device—be it because of failures or maintenance. SBD will terminate itself only if more than one device is lost and if required, depending on the status of the cluster partition or node. If at least two devices are still accessible, fencing messages can be successfully transmitted.

This configuration is suitable for more complex scenarios where storage is not restricted to a single array. Host-based mirroring solutions can have one SBD per mirror leg (not mirrored itself), and an additional tie-breaker on iSCSI.

Diskless

This configuration is useful if you want a fencing mechanism without shared storage. In this diskless mode, SBD fences nodes by using the hardware watchdog without relying on any shared device. However, diskless SBD cannot handle a split brain scenario for a two-node cluster. Therefore, three or more nodes are required for using diskless SBD.

11.5 Calculation of Timeouts

When using SBD as a fencing mechanism, it is vital to consider the timeouts of all components, because they depend on each other.

Watchdog Timeout

This timeout is set during initialization of the SBD device. It depends mostly on your storage latency. The majority of devices must be successfully read within this time. Otherwise, the node might self-fence.

Note
Note: Multipath or iSCSI Setup

If your SBD device(s) reside on a multipath setup or iSCSI, the timeout should be set to the time required to detect a path failure and switch to the next path.

This also means that in /etc/multipath.conf the value of max_polling_interval must be less than watchdog timeout.

msgwait Timeout

This timeout is set during initialization of the SBD device. It defines the time after which a message written to a node's slot on the SBD device is considered delivered. The timeout should be long enough for the node to detect that it needs to self-fence.

However, if the msgwait timeout is relatively long, a fenced cluster node might rejoin before the fencing action returns. This can be mitigated by setting the SBD_DELAY_START parameter in the SBD configuration, as described in Procedure 11.4 in Step 4.

stonith-timeout in the CIB

This timeout is set in the CIB as a global cluster property. It defines how long to wait for the STONITH action (reboot, on, off) to complete.

stonith-watchdog-timeout in the CIB

This timeout is set in the CIB as a global cluster property. If not set explicitly, it defaults to 0, which is appropriate for using SBD with one to three devices. For use of SBD in diskless mode, see Procedure 11.8, “Configuring Diskless SBD” for more details.

If you change the watchdog timeout, you need to adjust the other two timeouts as well. The following formula expresses the relationship between these three values:

Example 11.1: Formula for Timeout Calculation
Timeout (msgwait) = (Timeout (watchdog) * 2)
stonith-timeout = Timeout (msgwait) + 20%

For example, if you set the watchdog timeout to 120, set the msgwait timeout to 240 and the stonith-timeout to 288.

If you use the ha-cluster-bootstrap scripts to set up a cluster and to initialize the SBD device, the relationship between these timeouts is automatically considered.

11.6 Setting Up the Watchdog

SUSE Linux Enterprise High Availability Extension ships with several kernel modules that provide hardware-specific watchdog drivers. For a list of the most commonly used ones, see Commonly Used Watchdog Drivers.

For clusters in production environments we recommend to use a hardware-specific watchdog driver. However, if no watchdog matches your hardware, softdog can be used as kernel watchdog module.

The High Availability Extension uses the SBD daemon as the software component that feeds the watchdog.

11.6.1 Using a Hardware Watchdog

Finding the right watchdog kernel module for a given system is not trivial. Automatic probing fails very often. As a result, lots of modules are already loaded before the right one gets a chance.

Table 11.1 lists the most commonly used watchdog drivers. If your hardware is not listed there, the directory /lib/modules/KERNEL_VERSION/kernel/drivers/watchdog gives you a list of choices, too. Alternatively, ask your hardware vendor for the name.

Table 11.1: Commonly Used Watchdog Drivers
HardwareDriver
HPhpwdt
Dell, Fujitsu, Lenovo (Intel TCO)iTCO_wdt
VM on z/VM on IBM mainframevmwatchdog
Xen VM (DomU)xen_xdt
Genericsoftdog
Important
Important: Accessing the Watchdog Timer

Some hardware vendors ship systems management software that uses the watchdog for system resets (for example, HP ASR daemon). If the watchdog is used by SBD, disable such software. No other software must access the watchdog timer.

Procedure 11.1: Loading the Correct Kernel Module

To make sure the correct watchdog module is loaded, proceed as follows:

  1. List the drivers that have been installed with your kernel version:

    root # rpm -ql kernel-VERSION | grep watchdog
  2. List any watchdog modules that are currently loaded in the kernel:

    root # lsmod | egrep "(wd|dog)"
  3. If you get a result, unload the wrong module:

    root # rmmod WRONG_MODULE
  4. Enable the watchdog module that matches your hardware:

    root # echo WATCHDOG_MODULE > /etc/modules-load.d/watchdog.conf
    root # systemctl restart systemd-modules-load
  5. Test whether the watchdog module is loaded correctly:

    root # lsmod | grep dog

11.6.2 Using the Software Watchdog (softdog)

For clusters in production environments we recommend to use a hardware-specific watchdog driver. However, if no watchdog matches your hardware, softdog can be used as kernel watchdog module.

Important
Important: Softdog Limitations

The softdog driver assumes that at least one CPU is still running. If all CPUs are stuck, the code in the softdog driver that should reboot the system will never be executed. In contrast, hardware watchdogs keep working even if all CPUs are stuck.

Procedure 11.2: Loading the Softdog Kernel Module
  1. Enable the softdog driver:

    root # echo softdog > /etc/modules-load.d/watchdog.conf
  2. Add the softdog module in /etc/modules-load.d/watchdog.conf and restart a service:

    root # echo softdog > /etc/modules-load.d/watchdog.conf
    root # systemctl restart systemd-modules-load
  3. Test whether the softdog watchdog module is loaded correctly:

    root # lsmod | grep softdog

11.7 Setting Up SBD with Devices

The following steps are necessary for setup:

Before you start, make sure the block device or devices you want to use for SBD meet the requirements specified in Section 11.3.

When setting up the SBD devices, you need to take several timeout values into account. For details, see Section 11.5, “Calculation of Timeouts”.

The node will terminate itself if the SBD daemon running on it has not updated the watchdog timer fast enough. After having set the timeouts, test them in your specific environment.

Procedure 11.3: Initializing the SBD Devices

To use SBD with shared storage, you must first create the messaging layout on one to three block devices. The sbd create command will write a metadata header to the specified device or devices. It will also initialize the messaging slots for up to 255 nodes. If executed without any further options, the command will use the default timeout settings.

Warning
Warning: Overwriting Existing Data

Make sure the device or devices you want to use for SBD do not hold any important data. When you execute the sbd create command, roughly the first megabyte of the specified block devices will be overwritten without further requests or backup.

  1. Decide which block device or block devices to use for SBD.

  2. Initialize the SBD device with the following command:

    root # sbd -d /dev/SBD create

    (Replace /dev/SBD with your actual path name, for example: /dev/disk/by-id/scsi-ST2000DM001-0123456_Wabcdefg).

    To use more than one device for SBD, specify the -d option multiple times, for example:

    root # sbd -d /dev/SBD1 -d /dev/SBD2 -d /dev/SBD3 create
  3. If your SBD device resides on a multipath group, use the -1 and -4 options to adjust the timeouts to use for SBD. For details, see Section 11.5, “Calculation of Timeouts”. All timeouts are given in seconds:

    root # sbd -d /dev/SBD -4 1801 -1 902 create

    1

    The -4 option is used to specify the msgwait timeout. In the example above, it is set to 180 seconds.

    2

    The -1 option is used to specify the watchdog timeout. In the example above, it is set to 90 seconds. The minimum allowed value for the emulated watchdog is 15 seconds.

  4. Check what has been written to the device:

    root # sbd -d /dev/SBD dump
    Header version     : 2.1
    UUID               : 619127f4-0e06-434c-84a0-ea82036e144c
    Number of slots    : 255
    Sector size        : 512
    Timeout (watchdog) : 5
    Timeout (allocate) : 2
    Timeout (loop)     : 1
    Timeout (msgwait)  : 10
    ==Header on disk /dev/SBD is dumped

    As you can see, the timeouts are also stored in the header, to ensure that all participating nodes agree on them.

After you have initialized the SBD devices, edit the SBD configuration file, then enable and start the respective services for the changes to take effect.

Procedure 11.4: Editing the SBD Configuration File
  1. Open the file /etc/sysconfig/sbd.

  2. Search for the following parameter: SBD_DEVICE.

    It specifies the devices to monitor and to use for exchanging SBD messages.

  3. Edit this line by replacing SBD with your SBD device:

    SBD_DEVICE="/dev/SBD"

    If you need to specify multiple devices in the first line, separate them with semicolons (the order of the devices does not matter):

    SBD_DEVICE="/dev/SBD1; /dev/SBD2; /dev/SBD3"

    If the SBD device is not accessible, the daemon will fail to start and inhibit cluster start-up.

  4. Search for the following parameter: SBD_DELAY_START.

    Enables or disables a delay. Set SBD_DELAY_START to yes if msgwait is relatively long, but your cluster nodes boot very fast. Setting this parameter to yes delays the start of SBD on boot. This is sometimes necessary with virtual machines.

After you have added your SBD devices to the SBD configuration file, enable the SBD daemon. The SBD daemon is a critical piece of the cluster stack. It needs to be running when the cluster stack is running. Thus, the sbd service is started as a dependency whenever the pacemaker service is started.

Procedure 11.5: Enabling and Starting the SBD Service
  1. On each node, enable the SBD service:

    root # systemctl enable sbd

    It will be started together with the Corosync service whenever the Pacemaker service is started.

  2. Restart the cluster stack on each node:

    root # systemctl stop pacemaker
    root # systemctl start pacemaker

    This automatically triggers the start of the SBD daemon.

As a next step, test the SBD devices as described in Procedure 11.6.

Procedure 11.6: Testing the SBD Devices
  1. The following command will dump the node slots and their current messages from the SBD device:

    root # sbd -d /dev/SBD list

    Now you should see all cluster nodes that have ever been started with SBD listed here. For example, if you have a two-node cluster, the message slot should show clear for both nodes:

    0       alice        clear
    1       bob          clear
  2. Try sending a test message to one of the nodes:

    root # sbd -d /dev/SBD message alice test
  3. The node will acknowledge the receipt of the message in the system log files:

    May 03 16:08:31 alice sbd[66139]: /dev/SBD: notice: servant: Received command test from bob on disk /dev/SBD

    This confirms that SBD is indeed up and running on the node and that it is ready to receive messages.

As a final step, you need to adjust the cluster configuration as described in Procedure 11.7.

Procedure 11.7: Configuring the Cluster to Use SBD

To configure the use of SBD in the cluster, you need to do the following in the cluster configuration:

  • Set the stonith-timeout parameter to a value that matches your setting.

  • Configure the SBD STONITH resource.

For the calculation of the stonith-timeout refer to Section 11.5, “Calculation of Timeouts”.

  1. Start a shell and log in as root or equivalent.

  2. Run crm configure.

  3. Enter the following:

    crm(live)configure# property stonith-enabled="true" 1
    crm(live)configure# property stonith-watchdog-timeout=0 2
    crm(live)configure# property stonith-timeout="40s" 3

    1

    This is the default configuration, because clusters without STONITH are not supported. But in case STONITH has been deactivated for testing purposes, make sure this parameter is set to true again.

    2

    If not explicitly set, this value defaults to 0, which is appropriate for use of SBD with one to three devices.

    3

    A stonith-timeout value of 40 would be appropriate if the msgwait timeout value for SBD was set to 30 seconds.

  4. For a two-node cluster, decide if you want predictable or random delays. For other cluster setups you do not need to set this parameter.

    Predictable Static Delays

    This parameter enables a static delay before executing STONITH actions. It ensures that the nodes do not fence each other if separate fencing resources and different delay values are being used. The targeted node will loose in a fencing race. The parameter can be used to mark a specific node to survive in case of a split-brain scenario in a two-node cluster. To make this succeed, it is essential to create two primitive STONITH devices for each node. In the following configuration, alice will win and survive in case of a split-brain scenario:

    crm(live)configure# primitive st-sbd-alice stonith:external/sbd params \
           pcmk_host_list=alice pcmk_delay_base=20
    crm(live)configure# primitive st-sbd-bob stonith:external/sbd params \
           pcmk_host_list=bob pcmk_delay_base=0
    Dynamic Random Delays

    This parameter prevents double fencing when using slow devices such as SBD. It adds a random delay for STONITH actions on the fencing device. It is especially important for two-node clusters where otherwise both nodes might try to fence each other in case of a split brain scenario.

    crm(live)configure# primitive stonith_sbd stonith:external/sbd
      params pcmk_delay_max=30
  5. Review your changes with show.

  6. Submit your changes with commit and leave the crm live configuration with exit.

After the resource has started, your cluster is successfully configured for use of SBD. It will use this method in case a node needs to be fenced.

11.8 Setting Up Diskless SBD

SBD can be operated in a diskless mode. In this mode, a watchdog device will be used to reset the node in the following cases: if it loses quorum, if any monitored daemon is lost and not recovered, or if Pacemaker decides that the node requires fencing. Diskless SBD is based on self-fencing of a node, depending on the status of the cluster, the quorum and some reasonable assumptions. No STONITH SBD resource primitive is needed in the CIB.

Important
Important: Number of Cluster Nodes

Do not use diskless SBD as a fencing mechanism for two-node clusters. Use it only in clusters with three or more nodes. SBD in diskless mode cannot handle split brain scenarios for two-node clusters.

Procedure 11.8: Configuring Diskless SBD
  1. Open the file /etc/sysconfig/sbd and use the following entries:

    SBD_PACEMAKER=yes
    SBD_STARTMODE=always
    SBD_DELAY_START=no
    SBD_WATCHDOG_DEV=/dev/watchdog
    SBD_WATCHDOG_TIMEOUT=5

    The SBD_DEVICE entry is not needed as no shared disk is used. When this parameter is missing, the sbd service does not start any watcher process for SBD devices.

  2. On each node, enable the SBD service:

    root # systemctl enable sbd

    It will be started together with the Corosync service whenever the Pacemaker service is started.

  3. Restart the cluster stack on each node:

    root # systemctl stop pacemaker
    root # systemctl start pacemaker

    This automatically triggers the start of the SBD daemon.

  4. Check if the parameter have-watchdog=true has been automatically set:

    root # crm configure show | grep have-watchdog
             have-watchdog=true
  5. Run crm configure and set the following cluster properties on the crm shell:

    crm(live)configure# property stonith-enabled="true" 1
    crm(live)configure# property stonith-watchdog-timeout=10 2

    1

    This is the default configuration, because clusters without STONITH are not supported. But in case STONITH has been deactivated for testing purposes, make sure this parameter is set to true again.

    2

    For diskless SBD, this parameter must not equal zero. It defines after how long it is assumed that the fencing target has already self-fenced. Therefore its value needs to be >= the value of SBD_WATCHDOG_TIMEOUT in /etc/sysconfig/sbd. Starting with SUSE Linux Enterprise High Availability Extension 15, if you set stonith-watchdog-timeout to a negative value, Pacemaker will automatically calculate this timeout and set it to twice the value of SBD_WATCHDOG_TIMEOUT.

  6. Review your changes with show.

  7. Submit your changes with commit and leave the crm live configuration with exit.

11.9 Testing SBD and Fencing

To test whether SBD works as expected for node fencing purposes, use one or all of the following methods:

Manually Triggering Fencing of a Node

To trigger a fencing action for node NODENAME:

root # crm node fence NODENAME

Check if the node is fenced and if the other nodes consider the node as fenced after the stonith-watchdog-timeout.

Simulating an SBD Failure
  1. Identify the process ID of the SBD inquisitor:

    root # systemctl status sbd
    ● sbd.service - Shared-storage based fencing daemon
    
       Loaded: loaded (/usr/lib/systemd/system/sbd.service; enabled; vendor preset: disabled)
       Active: active (running) since Tue 2018-04-17 15:24:51 CEST; 6 days ago
         Docs: man:sbd(8)
      Process: 1844 ExecStart=/usr/sbin/sbd $SBD_OPTS -p /var/run/sbd.pid watch (code=exited, status=0/SUCCESS)
     Main PID: 1859 (sbd)
        Tasks: 4 (limit: 4915)
       CGroup: /system.slice/sbd.service
               ├─1859 sbd: inquisitor
    [...]
  2. Simulate an SBD failure by terminating the SBD inquisitor process. In our example, the process ID of the SBD inquisitor is 1859):

    root # kill -9 1859

    The node proactively self-fences. The other nodes notice the loss of the node and consider it has self-fenced after the stonith-watchdog-timeout.

Triggering Fencing through a Monitor Operation Failure

With a normal configuration, a failure of a resource stop operation will trigger fencing. To trigger fencing manually, you can produce a failure of a resource stop operation. Alternatively, you can temporarily change the configuration of a resource monitor operation and produce a monitor failure as described below:

  1. Configure an on-fail=fence property for a resource monitor operation:

    op monitor interval=10 on-fail=fence
  2. Let the monitoring operation fail (for example, by terminating the respective daemon, if the resource relates to a service).

    This failure triggers a fencing action.

11.10 Additional Mechanisms for Storage Protection

Apart from node fencing via STONITH there are other methods to achieve storage protection at a resource level. For example, SCSI-3 and SCSI-4 use persistent reservations whereas sfex provides a locking mechanism. Both methods are explained in the following subsections.

11.10.1 Configuring an sg_persist Resource

The SCSI specification 3 and 4 define persistent reservations. These are SCSI protocol features and can be used for I/O fencing and failover. This feature is implemented in the sg_persist Linux command.

Note
Note: SCSI Disk Compatibility

Any backing disks for sg_persist must be SCSI disk compatible. sg_persist only works for devices like SCSI disks or iSCSI LUNs. Do not use it for IDE, SATA, or any block devices which do not support the SCSI protocol.

Before you proceed, check if your disk supports persistent reservations. Use the following command (replace DISK with your device name):

root # sg_persist -n --in --read-reservation -d /dev/DISK

The result shows whether your disk supports persistent reservations:

  • Supported disk:

    PR generation=0x0, there is NO reservation held
  • Unsupported disk:

    PR in (Read reservation): command not supported
    Illegal request, Invalid opcode

If you get an error message (like the one above), replace the old disk with an SCSI compatible disk. Otherwise proceed as follows:

  1. To create the primitive resource sg_persist, run the following commands as root:

    root # crm configure
    crm(live)configure# primitive sg sg_persist \
        params devs="/dev/sdc" reservation_type=3 \
        op monitor interval=60 timeout=60
  2. Add the sg_persist primitive to a master-slave group:

    crm(live)configure# ms ms-sg sg \
        meta master-max=1 notify=true
  3. Do some tests. When the resource is in master/slave status, on the master server, you can mount and write on /dev/sdc1, while on the slave server you cannot write.

  4. Add a file system primitive for Ext4:

    crm(live)configure# primitive ext4 ocf:heartbeat:Filesystem \
        params device="/dev/sdc1" directory="/mnt/ext4" fstype=ext4
  5. Add the following order relationship plus a collocation between the sg_persist master and the file system resource:

    crm(live)configure# order o-ms-sg-before-ext4 inf: ms-sg:promote ext4:start
    crm(live)configure# colocation col-ext4-with-sg-persist inf: ext4 ms-sg:Master
  6. Check all your changes with the show command.

  7. Commit your changes.

For more information, refer to the sg_persist man page.

11.10.2 Ensuring Exclusive Storage Activation with sfex

This section introduces sfex, an additional low-level mechanism to lock access to shared storage exclusively to one node. Note that sfex does not replace STONITH. As sfex requires shared storage, it is recommended that the SBD node fencing mechanism described above is used on another partition of the storage.

By design, sfex cannot be used with workloads that require concurrency (such as OCFS2). It serves as a layer of protection for classic failover style workloads. This is similar to an SCSI-2 reservation in effect, but more general.

11.10.2.1 Overview

In a shared storage environment, a small partition of the storage is set aside for storing one or more locks.

Before acquiring protected resources, the node must first acquire the protecting lock. The ordering is enforced by Pacemaker. The sfex component ensures that even if Pacemaker were subject to a split brain situation, the lock will never be granted more than once.

These locks must also be refreshed periodically, so that a node's death does not permanently block the lock and other nodes can proceed.

11.10.2.2 Setup

In the following, learn how to create a shared partition for use with sfex and how to configure a resource for the sfex lock in the CIB. A single sfex partition can hold any number of locks, and needs 1 KB of storage space allocated per lock. By default, sfex_init creates one lock on the partition.

Important
Important: Requirements
  • The shared partition for sfex should be on the same logical unit as the data you want to protect.

  • The shared sfex partition must not use host-based RAID, nor DRBD.

  • Using an LVM2 logical volume is possible.

Procedure 11.9: Creating an sfex Partition
  1. Create a shared partition for use with sfex. Note the name of this partition and use it as a substitute for /dev/sfex below.

  2. Create the sfex metadata with the following command:

    root # sfex_init -n 1 /dev/sfex
  3. Verify that the metadata has been created correctly:

    root # sfex_stat -i 1 /dev/sfex ; echo $?

    This should return 2, since the lock is not currently held.

Procedure 11.10: Configuring a Resource for the sfex Lock
  1. The sfex lock is represented via a resource in the CIB, configured as follows:

    crm(live)configure# primitive sfex_1 ocf:heartbeat:sfex \
    #	params device="/dev/sfex" index="1" collision_timeout="1" \
          lock_timeout="70" monitor_interval="10" \
    #	op monitor interval="10s" timeout="30s" on-fail="fence"
  2. To protect resources via an sfex lock, create mandatory ordering and placement constraints between the resources to protect and the sfex resource. If the resource to be protected has the ID filesystem1:

    crm(live)configure# order order-sfex-1 inf: sfex_1 filesystem1
    crm(live)configure# colocation colo-sfex-1 inf: filesystem1 sfex_1
  3. If using group syntax, add the sfex resource as the first resource to the group:

    crm(live)configure# group LAMP sfex_1 filesystem1 apache ipaddr

11.11 For More Information

12 Access Control Lists

Abstract

The cluster administration tools like crm shell (crmsh) or Hawk2 can be used by root or any user in the group haclient. By default, these users have full read/write access. To limit access or assign more fine-grained access rights, you can use Access control lists (ACLs).

Access control lists consist of an ordered set of access rules. Each rule allows read or write access or denies access to a part of the cluster configuration. Rules are typically combined to produce a specific role, then users may be assigned to a role that matches their tasks.

Note
Note: CIB Syntax Validation Version and ACL Differences

This ACL documentation only applies if your CIB is validated with the CIB syntax version pacemaker-2.0 or higher. For details on how to check this and upgrade the CIB version, see Note: Upgrading the CIB Syntax Version.

If you have upgraded from SUSE Linux Enterprise High Availability Extension 11 SPx and kept your former CIB version, refer to the Access Control List chapter in the Administration Guide for SUSE Linux Enterprise High Availability Extension 11 SP3 or earlier. It is available from http://www.suse.com/documentation/.

12.1 Requirements and Prerequisites

Before you start using ACLs on your cluster, make sure the following conditions are fulfilled:

  • Ensure you have the same users on all nodes in your cluster, either by using NIS, Active Directory, or by manually adding the same users to all nodes.

  • All users for whom you want to modify access rights with ACLs must belong to the haclient group.

  • All users need to run crmsh by its absolute path /usr/sbin/crm.

  • If non-privileged users want to run crmsh, their PATH variable needs to be extended with /usr/sbin.

Important
Important: Default Access Rights
  • ACLs are an optional feature. By default, use of ACLs is disabled.

  • If ACLs are not enabled, root and all users belonging to the haclient group have full read/write access to the cluster configuration.

  • Even if ACLs are enabled and configured, both root and the default CRM owner hacluster always have full access to the cluster configuration.

To use ACLs you need some knowledge about XPath. XPath is a language for selecting nodes in an XML document. Refer to http://en.wikipedia.org/wiki/XPath or look into the specification at http://www.w3.org/TR/xpath/.

12.2 Enabling Use of ACLs in Your Cluster

Before you can start configuring ACLs, you need to enable use of ACLs. To do so, use the following command in the crmsh:

root # crm configure property enable-acl=true

Alternatively, use Hawk2 as described in Procedure 12.1, “Enabling Use of ACLs with Hawk2”.

Procedure 12.1: Enabling Use of ACLs with Hawk2
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Cluster Configuration to display the global cluster options and their current values.

  3. Below Cluster Configuration click the empty drop-down box and select enable-acl to add the parameter. It is added with its default value No.

  4. Set its value to Yes and apply your changes.

12.3 The Basics of ACLs

Access control lists consist of an ordered set of access rules. Each rule allows read or write access or denies access to a part of the cluster configuration. Rules are typically combined to produce a specific role, then users may be assigned to a role that matches their tasks. An ACL role is a set of rules which describe access rights to CIB. A rule consists of the following:

  • an access right like read, write, or deny

  • a specification where to apply the rule. This specification can be a type, an ID reference, or an XPath expression.

Usually, it is convenient to bundle ACLs into roles and assign a specific role to system users (ACL targets). There are two methods to create ACL rules:

12.3.1 Setting ACL Rules via XPath Expressions

To manage ACL rules via XPath, you need to know the structure of the underlying XML. Retrieve the structure with the following command that shows your cluster configuration in XML (see Example 12.1):

root # crm configure show xml
Example 12.1: Excerpt of a Cluster Configuration in XML
<num_updates="59" 
      dc-uuid="175704363"
      crm_feature_set="3.0.9"
      validate-with="pacemaker-2.0"
      epoch="96"
      admin_epoch="0"
      cib-last-written="Fri Aug  8 13:47:28 2014"
      have-quorum="1">
  <configuration>
    <crm_config>
       <cluster_property_set id="cib-bootstrap-options">
        <nvpair name="stonith-enabled" value="true" id="cib-bootstrap-options-stonith-enabled"/>
       [...]
      </cluster_property_set>
    </crm_config>
    <nodes>
      <node id="175704363" uname="alice"/>
      <node id="175704619" uname="bob"/>
    </nodes>
    <resources> [...]  </resources>
    <constraints/>
    <rsc_defaults> [...] </rsc_defaults>
    <op_defaults> [...] </op_defaults>
  <configuration>
</cib>

With the XPath language you can locate nodes in this XML document. For example, to select the root node (cib) use the XPath expression /cib. To locate the global cluster configurations, use the XPath expression /cib/configuration/crm_config.

As an example, Table 12.1, “Operator Role—Access Types and XPath Expressions” shows the parameters (access type and XPath expression) to create an operator role. Users with this role can only execute the tasks mentioned in the second column—they cannot reconfigure any resources (for example, change parameters or operations), nor change the configuration of colocation or ordering constraints.

Table 12.1: Operator Role—Access Types and XPath Expressions

Type

XPath/Explanation

Write

//crm_config//nvpair[@name='maintenance-mode']

Turn cluster maintenance mode on or off.

Write

//op_defaults//nvpair[@name='record-pending']

Choose whether pending operations are recorded.

Write

//nodes/node//nvpair[@name='standby']

Set node in online or standby mode.

Write

//resources//nvpair[@name='target-role']

Start, stop, promote or demote any resource.

Write

//resources//nvpair[@name='maintenance']

Select if a resource should be put to maintenance mode or not.

Write

//constraints/rsc_location

Migrate/move resources from one node to another.

Read

/cib

View the status of the cluster.

12.3.2 Setting ACL Rules via Abbreviations

For users who do not want to deal with the XML structure there is an easier method.

For example, consider the following XPath:

//*[@id='rsc1']

which locates all the XML nodes with the ID rsc1.

The abbreviated syntax is written like this:

ref:"rsc1"

This also works for constraints. Here is the verbose XPath:

//constraints/rsc_location

The abbreviated syntax is written like this:

type:"rsc_location"

The abbreviated syntax can be used in crmsh and Hawk2. The CIB daemon knows how to apply the ACL rules to the matching objects.

12.4 Configuring ACLs with Hawk2

The following procedures show how to configure read-only access to the cluster configuration by defining a monitor role and assigning it to a user. Alternatively, you can use crmsh to do so, as described in Procedure 12.4, “Adding a Monitor Role and Assigning a User with crmsh”.

Procedure 12.2: Adding a Monitor Role with Hawk2
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Roles.

  3. Click Create.

  4. Enter a unique Role ID, for example, monitor.

  5. As access Right, select Read.

  6. As Xpath, enter the Xpath expression /cib.

  7. Click Create.

    This creates a new role with the name monitor, sets the read rights and applies this to all elements in the CIB by using the XPath expression/cib.

  8. If necessary, add more rules by clicking the plus icon and specifying the respective parameters.

  9. Sort the individual rules by using the arrow up or down buttons.

Procedure 12.3: Assigning a Role to a Target with Hawk2

To assign the role we created in Procedure 12.2 to a system user (target), proceed as follows:

  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Targets.

  3. To create a system user (ACL Target), click Create and enter a unique Target ID, for example, tux. Make sure this user belongs to the haclient group.

  4. To assign a role to the target, select one or multiple Roles.

    In our example, select the monitor role you created in Procedure 12.2.

  5. Confirm your choice.

To configure access rights for resources or constraints, you can also use the abbreviated syntax as explained in Section 12.3.2, “Setting ACL Rules via Abbreviations”.

12.5 Configuring ACLs with crmsh

The following procedure shows how to configure a read-only access to the cluster configuration by defining a monitor role and assigning it to a user.

Procedure 12.4: Adding a Monitor Role and Assigning a User with crmsh
  1. Log in as root.

  2. Start the interactive mode of crmsh:

    root # crm configure
    crm(live)configure# 
  3. Define your ACL role(s):

    1. Use the role command to define a new role:

      crm(live)configure# role monitor read xpath:"/cib"

      The previous command creates a new role with the name monitor, sets the read rights and applies it to all elements in the CIB by using the XPath expression /cib. If necessary, you can add more access rights and XPath arguments.

    2. Add additional roles as needed.

  4. Assign your roles to one or multiple ACL targets, which are the corresponding system users. Make sure they belong to the haclient group.

    crm(live)configure# acl_target tux monitor
  5. Check your changes:

    crm(live)configure# show
  6. Commit your changes:

    crm(live)configure# commit

To configure access rights for resources or constraints, you can also use the abbreviated syntax as explained in Section 12.3.2, “Setting ACL Rules via Abbreviations”.

13 Network Device Bonding

Abstract

For many systems, it is desirable to implement network connections that comply to more than the standard data security or availability requirements of a typical Ethernet device. In these cases, several Ethernet devices can be aggregated to a single bonding device.

The configuration of the bonding device is done by means of bonding module options. The behavior is determined through the mode of the bonding device. By default, this is mode=active-backup, which means that a different slave device will become active if the active slave fails.

When using Corosync, the bonding device is not managed by the cluster software. Therefore, the bonding device must be configured on each cluster node that might possibly need to access the bonding device.

13.1 Configuring Bonding Devices with YaST

To configure a bonding device, you need to have multiple Ethernet devices that can be aggregated to a single bonding device. Proceed as follows:

  1. Start YaST as root and select System › Network Settings.

  2. In the Network Settings, switch to the Overview tab, which shows the available devices.

  3. Check if the Ethernet devices to be aggregate to a bonding device have an IP address assigned. If yes, change it:

    1. Select the device to change and click Edit.

    2. In the Address tab of the Network Card Setup dialog that opens, select the option No Link and IP Setup (Bonding Slaves).

    3. Click Next to return to the Overview tab in the Network Settings dialog.

  4. To add a new bonding device:

    1. Click Add and set the Device Type to Bond. Proceed with Next.

    2. Select how to assign the IP address to the bonding device. Three methods are at your disposal:

      • No Link and IP Setup (Bonding Slaves)

      • Dynamic Address (with DHCP or Zeroconf)

      • Statically assigned IP Address

      Use the method that is appropriate for your environment. If Corosync manages virtual IP addresses, select Statically assigned IP Address and assign an IP address to the interface.

    3. Switch to the Bond Slaves tab.

    4. It shows any Ethernet devices that have been configured as bonding slaves in Step 3.b. To select the Ethernet devices that you want to include into the bond, below Bond Slaves and Order activate the check box in front of the respective devices.

    5. Edit the Bond Driver Options. The following modes are available:

      balance-rr

      Provides load balancing and fault tolerance, at the cost of out-of-order packet transmission. This may cause delays, for example, for TCP reassembly.

      active-backup

      Provides fault tolerance.

      balance-xor

      Provides load balancing and fault tolerance.

      broadcast

      Provides fault tolerance.

      802.3ad

      Provides dynamic link aggregation if supported by the connected switch.

      balance-tlb

      Provides load balancing for outgoing traffic.

      balance-alb

      Provides load balancing for incoming and outgoing traffic, if the network devices used allow the modifying of the network device's hardware address while in use.

    6. Make sure to add the parameter miimon=100 to Bond Driver Options. Without this parameter, the link is not checked regularly, so the bonding driver might continue to lose packets on a faulty link.

  5. Click Next and leave YaST with OK to finish the configuration of the bonding device. YaST writes the configuration to /etc/sysconfig/network/ifcfg-bondDEVICENUMBER.

13.2 Hotplugging of Bonding Slaves

Sometimes it is necessary to replace a bonding slave interface with another one, for example, if the respective network device constantly fails. The solution is to set up hotplugging bonding slaves. It is also necessary to change the udev rules to match the device by bus ID instead of by MAC address. This enables you to replace defective hardware (a network card in the same slot but with a different MAC address), if the hardware allows for that.

Procedure 13.1: Configuring Hotplugging of Bonding Slaves with YaST

If you prefer manual configuration instead, refer to the SUSE Linux Enterprise Server SUSE Linux Enterprise High Availability Extension Administration Guide, chapter Basic Networking, section Hotplugging of Bonding Slaves.

  1. Start YaST as root and select System › Network Settings.

  2. In the Network Settings, switch to the Overview tab, which shows the already configured devices. If bonding slaves are already configured, the Note column shows it.

  3. For each of the Ethernet devices that have been aggregated to a bonding device, execute the following steps:

    1. Select the device to change and click Edit. The Network Card Setup dialog opens.

    2. Switch to the General tab and make sure that Activate device is set to On Hotplug.

    3. Switch to the Hardware tab.

    4. For the Udev rules, click Change and select the BusID option.

    5. Click OK and Next to return to the Overview tab in the Network Settings dialog. If you click the Ethernet device entry now, the bottom pane shows the device's details, including the bus ID.

  4. Click OK to confirm your changes and leave the network settings.

At boot time, the network setup does not wait for the hotplug slaves, but for the bond to become ready, which needs at least one available slave. When one of the slave interfaces is removed from the system (unbind from NIC driver, rmmod of the NIC driver or true PCI hotplug removal), the Kernel removes it from the bond automatically. When a new card is added to the system (replacement of the hardware in the slot), udev renames it by applying the bus-based persistent name rule and calls ifup for it. The ifup call automatically joins it into the bond.

13.3 For More Information

All modes and many other options are explained in detail in the Linux Ethernet Bonding Driver HOWTO. The file can be found at /usr/src/linux/Documentation/networking/bonding.txt after you have installed the package kernel-source.

For High Availability setups, the following options described therein are especially important: miimon and use_carrier.

14 Load Balancing

Abstract

Load Balancing makes a cluster of servers appear as one large, fast server to outside clients. This apparent single server is called a virtual server. It consists of one or more load balancers dispatching incoming requests and several real servers running the actual services. With a load balancing setup of High Availability Extension, you can build highly scalable and highly available network services, such as Web, cache, mail, FTP, media and VoIP services.

14.1 Conceptual Overview

High Availability Extension supports two technologies for load balancing: Linux Virtual Server (LVS) and HAProxy. The key difference is Linux Virtual Server operates at OSI layer 4 (Transport), configuring the network layer of kernel, while HAProxy operates at layer 7 (Application), running in user space. Thus Linux Virtual Server needs fewer resources and can handle higher loads, while HAProxy can inspect the traffic, do SSL termination and make dispatching decisions based on the content of the traffic.

On the other hand, Linux Virtual Server includes two different software: IPVS (IP Virtual Server) and KTCPVS (Kernel TCP Virtual Server). IPVS provides layer 4 load balancing whereas KTCPVS provides layer 7 load balancing.

This section gives you a conceptual overview of load balancing in combination with high availability, then briefly introduces you to Linux Virtual Server and HAProxy. Finally, it points you to further reading.

The real servers and the load balancers may be interconnected by either high-speed LAN or by geographically dispersed WAN. The load balancers dispatch requests to the different servers. They make parallel services of the cluster appear as one virtual service on a single IP address (the virtual IP address or VIP). Request dispatching can use IP load balancing technologies or application-level load balancing technologies. Scalability of the system is achieved by transparently adding or removing nodes in the cluster.

High availability is provided by detecting node or service failures and reconfiguring the whole virtual server system appropriately, as usual.

There are several load balancing strategies. Here are some Layer 4 strategies, suitable for Linux Virtual Server:

  • Round Robin.  The simplest strategy is to direct each connection to a different address, taking turns. For example, a DNS server can have several entries for a given host name. With DNS roundrobin, the DNS server will return all of them in a rotating order. Thus different clients will see different addresses.

  • Selecting the best server.  Although this has several drawbacks, balancing could be implemented with an the first server who responds or the least loaded server approach.

  • Balance number of connections per server.  A load balancer between users and servers can divide the number of users across multiple servers.

  • Geo Location.  It is possible to direct clients to a server nearby.

Here are some Layer 7 strategies, suitable for HAProxy:

  • URI.  Inspect the HTTP content and dispatch to a server most suitable for this specific URI.

  • URL parameter, RDP cookie.  Inspect the HTTP content for a session parameter, possibly in post parameters, or the RDP (remote desktop protocol) session cookie, and dispatch to the server serving this session.

Although there is some overlap, HAProxy can be used in scenarios where LVS/ipvsadm is not adequate and vice versa:

  • SSL termination.  The front-end load balancers can handle the SSL layer. Thus the cloud nodes do not need to have access to the SSL keys, or could take advantage of SSL accelerators in the load balancers.

  • Application level.  HAProxy operates at the application level, allowing the load balancing decisions to be influenced by the content stream. This allows for persistence based on cookies and other such filters.

On the other hand, LVS/ipvsadm cannot be fully replaced by HAProxy:

  • LVS supports direct routing, where the load balancer is only in the inbound stream, whereas the outbound traffic is routed to the clients directly. This allows for potentially much higher throughput in asymmetric environments.

  • LVS supports stateful connection table replication (via conntrackd). This allows for load balancer failover that is transparent to the client and server.

14.2 Configuring Load Balancing with Linux Virtual Server

The following sections give an overview of the main LVS components and concepts. Then we explain how to set up Linux Virtual Server on High Availability Extension.

14.2.1 Director

The main component of LVS is the ip_vs (or IPVS) Kernel code. It implements transport-layer load balancing inside the Linux Kernel (layer-4 switching). The node that runs a Linux Kernel including the IPVS code is called director. The IPVS code running on the director is the essential feature of LVS.

When clients connect to the director, the incoming requests are load-balanced across all cluster nodes: The director forwards packets to the real servers, using a modified set of routing rules that make the LVS work. For example, connections do not originate or terminate on the director, it does not send acknowledgments. The director acts as a specialized router that forwards packets from end users to real servers (the hosts that run the applications that process the requests).

By default, the Kernel does not need the IPVS module installed. The IPVS Kernel module is included in the cluster-network-kmp-default package.

14.2.2 User Space Controller and Daemons

The ldirectord daemon is a user-space daemon for managing Linux Virtual Server and monitoring the real servers in an LVS cluster of load balanced virtual servers. A configuration file, /etc/ha.d/ldirectord.cf, specifies the virtual services and their associated real servers and tells ldirectord how to configure the server as an LVS redirector. When the daemon is initialized, it creates the virtual services for the cluster.

By periodically requesting a known URL and checking the responses, the ldirectord daemon monitors the health of the real servers. If a real server fails, it will be removed from the list of available servers at the load balancer. When the service monitor detects that the dead server has recovered and is working again, it will add the server back to the list of available servers. In case that all real servers should be down, a fall-back server can be specified to which to redirect a Web service. Typically the fall-back server is localhost, presenting an emergency page about the Web service being temporarily unavailable.

The ldirectord uses the ipvsadm tool (package ipvsadm) to manipulate the virtual server table in the Linux Kernel.

14.2.3 Packet Forwarding

There are three different methods of how the director can send packets from the client to the real servers:

Network Address Translation (NAT)

Incoming requests arrive at the virtual IP. They are forwarded to the real servers by changing the destination IP address and port to that of the chosen real server. The real server sends the response to the load balancer which in turn changes the destination IP address and forwards the response back to the client. Thus, the end user receives the replies from the expected source. As all traffic goes through the load balancer, it usually becomes a bottleneck for the cluster.

IP Tunneling (IP-IP Encapsulation)

IP tunneling enables packets addressed to an IP address to be redirected to another address, possibly on a different network. The LVS sends requests to real servers through an IP tunnel (redirecting to a different IP address) and the real servers reply directly to the client using their own routing tables. Cluster members can be in different subnets.

Direct Routing

Packets from end users are forwarded directly to the real server. The IP packet is not modified, so the real servers must be configured to accept traffic for the virtual server's IP address. The response from the real server is sent directly to the client. The real servers and load balancers need to be in the same physical network segment.

14.2.4 Scheduling Algorithms

Deciding which real server to use for a new connection requested by a client is implemented using different algorithms. They are available as modules and can be adapted to specific needs. For an overview of available modules, refer to the ipvsadm(8) man page. Upon receiving a connect request from a client, the director assigns a real server to the client based on a schedule. The scheduler is the part of the IPVS Kernel code which decides which real server will get the next new connection.

More detailed description about Linux Virtual Server scheduling algorithms can be found at http://kb.linuxvirtualserver.org/wiki/IPVS. Furthermore, search for --scheduler in the ipvsadm man page.

Related load balancing strategies for HAProxy can be found at http://www.haproxy.org/download/1.6/doc/configuration.txt.

14.2.5 Setting Up IP Load Balancing with YaST

You can configure Kernel-based IP load balancing with the YaST IP Load Balancing module. It is a front-end for ldirectord.

To access the IP Load Balancing dialog, start YaST as root and select High Availability › IP Load Balancing. Alternatively, start the YaST cluster module as root on a command line with yast2 iplb.

The YaST module writes its configuration to /etc/ha.d/ldirectord.cf. The tabs available in the YaST module correspond to the structure of the /etc/ha.d/ldirectord.cf configuration file, defining global options and defining the options for the virtual services.

For an example configuration and the resulting processes between load balancers and real servers, refer to Example 14.1, “Simple ldirectord Configuration”.

Note
Note: Global Parameters and Virtual Server Parameters

If a certain parameter is specified in both the virtual server section and in the global section, the value defined in the virtual server section overrides the value defined in the global section.

Procedure 14.1: Configuring Global Parameters

The following procedure describes how to configure the most important global parameters. For more details about the individual parameters (and the parameters not covered here), click Help or refer to the ldirectord man page.

  1. With Check Interval, define the interval in which ldirectord will connect to each of the real servers to check if they are still online.

  2. With Check Timeout, set the time in which the real server should have responded after the last check.

  3. With Failure Count you can define how many times ldirectord will attempt to request the real servers until the check is considered failed.

  4. With Negotiate Timeout define a timeout in seconds for negotiate checks.

  5. In Fallback, enter the host name or IP address of the Web server onto which to redirect a Web service in case all real servers are down.

  6. If you want the system to send alerts in case the connection status to any real server changes, enter a valid e-mail address in Email Alert.

  7. With Email Alert Frequency, define after how many seconds the e-mail alert should be repeated if any of the real servers remains inaccessible.

  8. In Email Alert Status specify the server states for which e-mail alerts should be sent. If you want to define more than one state, use a comma-separated list.

  9. With Auto Reload define, if ldirectord should continuously monitor the configuration file for modification. If set to yes, the configuration is automatically reloaded upon changes.

  10. With the Quiescent switch, define whether to remove failed real servers from the Kernel's LVS table or not. If set to Yes, failed servers are not removed. Instead their weight is set to 0 which means that no new connections will be accepted. Already established connections will persist until they time out.

  11. If you want to use an alternative path for logging, specify a path for the log files in Log File. By default, ldirectord writes its log files to /var/log/ldirectord.log.

YaST IP Load Balancing—Global Parameters
Figure 14.1: YaST IP Load Balancing—Global Parameters
Procedure 14.2: Configuring Virtual Services

You can configure one or more virtual services by defining a couple of parameters for each. The following procedure describes how to configure the most important parameters for a virtual service. For more details about the individual parameters (and the parameters not covered here), click Help or refer to the ldirectord man page.

  1. In the YaST IP Load Balancing module, switch to the Virtual Server Configuration tab.

  2. Add a new virtual server or Edit an existing virtual server. A new dialog shows the available options.

  3. In Virtual Server enter the shared virtual IP address (IPv4 or IPv6) and port under which the load balancers and the real servers are accessible as LVS. Instead of IP address and port number you can also specify a host name and a service. Alternatively, you can also use a firewall mark. A firewall mark is a way of aggregating an arbitrary collection of VIP:port services into one virtual service.

  4. To specify the Real Servers, you need to enter the IP addresses (IPv4, IPv6, or host names) of the servers, the ports (or service names) and the forwarding method. The forwarding method must either be gate, ipip or masq, see Section 14.2.3, “Packet Forwarding”.

    Click the Add button and enter the required arguments for each real server.

  5. As Check Type, select the type of check that should be performed to test if the real servers are still alive. For example, to send a request and check if the response contains an expected string, select Negotiate.

  6. If you have set the Check Type to Negotiate, you also need to define the type of service to monitor. Select it from the Service drop-down box.

  7. In Request, enter the URI to the object that is requested on each real server during the check intervals.

  8. If you want to check if the response from the real servers contains a certain string (I'm alive message), define a regular expression that needs to be matched. Enter the regular expression into Receive. If the response from a real server contains this expression, the real server is considered to be alive.

  9. Depending on the type of Service you have selected in Step 6, you also need to specify further parameters for authentication. Switch to the Auth type tab and enter the details like Login, Password, Database, or Secret. For more information, refer to the YaST help text or to the ldirectord man page.

  10. Switch to the Others tab.

  11. Select the Scheduler to be used for load balancing. For information on the available schedulers, refer to the ipvsadm(8) man page.

  12. Select the Protocol to be used. If the virtual service is specified as an IP address and port, it must be either tcp or udp. If the virtual service is specified as a firewall mark, the protocol must be fwm.

  13. Define further parameters, if needed. Confirm your configuration with OK. YaST writes the configuration to /etc/ha.d/ldirectord.cf.

YaST IP Load Balancing—Virtual Services
Figure 14.2: YaST IP Load Balancing—Virtual Services
Example 14.1: Simple ldirectord Configuration

The values shown in Figure 14.1, “YaST IP Load Balancing—Global Parameters” and Figure 14.2, “YaST IP Load Balancing—Virtual Services”, would lead to the following configuration, defined in /etc/ha.d/ldirectord.cf:

autoreload = yes 1
    checkinterval = 5 2
    checktimeout = 3 3
    quiescent = yes 4
    virtual = 192.168.0.200:80 5
    checktype = negotiate 6
    fallback = 127.0.0.1:80 7
    protocol = tcp 8
    real = 192.168.0.110:80 gate 9
    real = 192.168.0.120:80 gate 9
    receive = "still alive" 10
    request = "test.html" 11
    scheduler = wlc 12
    service = http 13

1

Defines that ldirectord should continuously check the configuration file for modification.

2

Interval in which ldirectord will connect to each of the real servers to check if they are still online.

3

Time in which the real server should have responded after the last check.

4

Defines not to remove failed real servers from the Kernel's LVS table, but to set their weight to 0 instead.

5

Virtual IP address (VIP) of the LVS. The LVS is available at port 80.

6

Type of check that should be performed to test if the real servers are still alive.

7

Server onto which to redirect a Web service all real servers for this service are down.

8

Protocol to be used.

9

Two real servers defined, both available at port 80. The packet forwarding method is gate, meaning that direct routing is used.

10

Regular expression that needs to be matched in the response string from the real server.

11

URI to the object that is requested on each real server during the check intervals.

12

Selected scheduler to be used for load balancing.

13

Type of service to monitor.

This configuration would lead to the following process flow: The ldirectord will connect to each real server once every 5 seconds (2) and request 192.168.0.110:80/test.html or 192.168.0.120:80/test.html as specified in 9 and 11. If it does not receive the expected still alive string (10) from a real server within 3 seconds (3) of the last check, it will remove the real server from the available pool. However, because of the quiescent=yes setting (4), the real server will not be removed from the LVS table. Instead its weight will be set to 0 so that no new connections to this real server will be accepted. Already established connections will be persistent until they time out.

14.2.6 Further Setup

Apart from the configuration of ldirectord with YaST, you need to make sure the following conditions are fulfilled to complete the LVS setup:

  • The real servers are set up correctly to provide the needed services.

  • The load balancing server (or servers) must be able to route traffic to the real servers using IP forwarding. The network configuration of the real servers depends on which packet forwarding method you have chosen.

  • To prevent the load balancing server (or servers) from becoming a single point of failure for the whole system, you need to set up one or several backups of the load balancer. In the cluster configuration, configure a primitive resource for ldirectord, so that ldirectord can fail over to other servers in case of hardware failure.

  • As the backup of the load balancer also needs the ldirectord configuration file to fulfill its task, make sure the /etc/ha.d/ldirectord.cf is available on all servers that you want to use as backup for the load balancer. You can synchronize the configuration file with Csync2 as described in Section 4.5, “Transferring the Configuration to All Nodes”.

14.3 Configuring Load Balancing with HAProxy

The following section gives an overview of the HAProxy and how to set up on High Availability. The load balancer distributes all requests to its back-end servers. It is configured as active/passive, meaning if one master fails, the slave becomes the master. In such a scenario, the user will not notice any interruption.

In this section, we will use the following setup:

  • A load balancer, with the IP address 192.168.1.99.

  • A virtual, floating IP address 192.168.1.99.

  • Our servers (usually for Web content) www1.example.com (IP: 192.168.1.200) and www2.example.com (IP: 192.168.1.201)

To configure HAProxy, use the following procedure:

  1. Install the haproxy package.

  2. Create the file /etc/haproxy/haproxy.cfg with the following contents:

    global 1
      maxconn 256
      daemon
    
    defaults 2
      log     global
      mode    http
      option  httplog
      option  dontlognull
      retries 3
      option redispatch
      maxconn 2000
      timeout connect   5000  3
      timeout client    50s   4
      timeout server    50000 5
    
    frontend LB
      bind 192.168.1.99:80 6
      reqadd X-Forwarded-Proto:\ http
      default_backend LB
    
    backend LB
      mode http
      stats enable
      stats hide-version
      stats uri /stats
      stats realm Haproxy\ Statistics
      stats auth haproxy:password	7
      balance roundrobin	8
      option  httpclose
      option forwardfor
      cookie LB insert
      option httpchk GET /robots.txt HTTP/1.0
      server web1-srv 192.168.1.200:80 cookie web1-srv check
      server web2-srv 192.168.1.201:80 cookie web2-srv check

    1

    Section which contains process-wide and OS-specific options.

    maxconn

    Maximum per-process number of concurrent connections.

    daemon

    Recommended mode, HAProxy runs in the background.

    2

    Section which sets default parameters for all other sections following its declaration. Some important lines:

    redispatch

    Enables or disables session redistribution in case of connection failure.

    log

    Enables logging of events and traffic.

    mode http

    Operates in HTTP mode (recommended mode for HAProxy). In this mode, a request will be analyzed before a connection to any server is performed. Request that are not RFC-compliant will be rejected.

    option forwardfor

    Adds the HTTP X-Forwarded-For header into the request. You need this option if you want to preserve the client's IP address.

    3

    The maximum time to wait for a connection attempt to a server to succeed.

    4

    The maximum time of inactivity on the client side.

    5

    The maximum time of inactivity on the server side.

    6

    Section which combines front-end and back-end sections in one.

    balance leastconn

    Defines the load balancing algorithm, see http://cbonte.github.io/haproxy-dconv/configuration-1.5.html#4-balance.

    stats enable , stats auth

    Enables statistics reporting (by stats enable). The auth option logs statistics with authentication to a specific account.

    7

    Credentials for HAProxy Statistic report page.

    8

    Load balancing will work in a round-robin process.

  3. Test your configuration file:

    root # haproxy -f /etc/haproxy/haproxy.cfg -c
  4. Add the following line to Csync2's configuration file /etc/csync2/csync2.cfg to make sure the HAProxy configuration file is included:

    include /etc/haproxy/haproxy.cfg
  5. Synchronize it:

    root # csync2 -f /etc/haproxy/haproxy.cfg
    root # csync2 -xv
    Note
    Note

    The Csync2 configuration part assumes that the HA nodes were configured using ha-cluster-bootstrap. For details, see the Installation and Setup Quick Start.

  6. Make sure HAProxy is disabled on both load balancers (alice and bob) as it is started by Pacemaker:

    root # systemctl disable haproxy
  7. Configure a new CIB:

    root # crm configure
    crm(live)# cib new haproxy-config
    crm(haproxy-config)# primitive primitive haproxy systemd:haproxy \
        op start timeout=120 interval=0 \
        op stop timeout=120 interval=0 \
        op monitor timeout=100 interval=5s \
        meta target-role=Started
    crm(haproxy-config)# primitive vip IPaddr2 \
        params ip=192.168.1.99 nic=eth0 cidr_netmask=23 broadcast=192.168.1.255 \
        op monitor interval=5s timeout=120 on-fail=restart \
        meta target-role=Started
    crm(haproxy-config)# order haproxy-after-IP Mandatory: vip haproxy
    crm(haproxy-config)# colocation haproxy-with-public-IPs inf: haproxy vip
    crm(haproxy-config)# group g-haproxy vip haproxy-after-IP
  8. Verify the new CIB and correct any errors:

    crm(haproxy-config)# verify
  9. Commit the new CIB:

    crm(haproxy-config)# cib use live
    crm(live)# cib commit haproxy-config

14.4 For More Information

15 Geo Clusters (Multi-Site Clusters)

Abstract

Apart from local clusters and metro area clusters, SUSE® Linux Enterprise High Availability Extension 12 SP3 also supports geographically dispersed clusters (Geo clusters, sometimes also called multi-site clusters). That means you can have multiple, geographically dispersed sites with a local cluster each. Failover between these clusters is coordinated by a higher level entity, the so-called booth. Support for Geo clusters is available as a separate extension to Geo Clustering for SUSE Linux Enterprise High Availability Extension. For details on how to use and set up Geo clusters, refer to the Geo Clustering Quick Start or the Geo Clustering Guide. Both are available from http://www.suse.com/documentation/sle-ha-geo-12.

16 Executing Maintenance Tasks

Abstract

To perform maintenance tasks on the cluster nodes, you might need to stop the resources running on that node, to move them, or to shut down or reboot the node. It might also be necessary to temporarily take over the control of resources from the cluster, or even to stop the cluster service while resources remain running.

This chapter explains how to manually take down a cluster node without negative side-effects. It also gives an overview of different options the cluster stack provides for executing maintenance tasks.

16.1 Implications of Taking Down a Cluster Node

When you shut down or reboot a cluster node (or stop the Pacemaker service on a node), the following processes will be triggered:

  • The resources that are running on the node will be stopped or moved off the node.

  • If stopping the resources should fail or time out, the STONITH mechanism will fence the node and shut it down.

Procedure 16.1: Manually Rebooting a Cluster Node

If your aim is to move the services off the node in an orderly fashion before shutting down or rebooting the node, proceed as follows:

  1. On the node you want to reboot or shut down, log in as root or equivalent.

  2. Put the node into standby mode:

    root # crm node standby

    That way, services can migrate off the node without being limited by the shutdown timeout of Pacemaker.

  3. Check the cluster status with:

    root # crm status

    It shows the respective node in standby mode:

    [...]
    Node bob: standby
    [...]
  4. Stop the Pacemaker service on that node:

    root # systemctl stop pacemaker.service
  5. Reboot the node.

To check if the node joins the cluster again:

  1. Log in to the node as root or equivalent.

  2. Check if the Pacemaker service has started:

    root # systemctl status pacemaker.service
  3. If not, start it:

    root # systemctl start pacemaker.service
  4. Check the cluster status with:

    root # crm status

    It should show the node coming online again.

16.2 Different Options for Maintenance Tasks

Pacemaker offers a variety of options for performing system maintenance:

Putting the Cluster Into Maintenance Mode

The global cluster property maintenance-mode allows you to put all resources into maintenance state at once. The cluster will cease monitoring them and thus become oblivious to their status.

Putting a Node Into Maintenance Mode

This option allows you to put all resources running on a specific node into maintenance state at once. The cluster will cease monitoring them and thus become oblivious to their status.

Putting a Node Into Standby Mode

A node that is in standby mode can no longer run resources. Any resources running on the node will be moved away or stopped (in case no other node is eligible to run the resource). Also, all monitor operations will be stopped on the node (except for those with role="Stopped").

You can use this option if you need to stop a node in a cluster while continuing to provide the services running on another node.

Putting a Resource Into Maintenance Mode

When this mode is enabled for a resource, no monitor operations will be triggered for the resource.

Use this option if you need to manually touch the service that is managed by this resource and do not want the cluster to run any monitoring operations for the resource during that time.

Putting a Resource Into Unmanaged Mode

The is-managed meta attribute allows you to temporarily release a resource from being managed by the cluster stack. This means you can manually touch the service that is managed by this resource (for example, to adjust any components). However, the cluster will continue to monitor the resource and to report any failures.

If you want the cluster to also cease monitoring the resource, use the per-resource maintenance mode instead (see Putting a Resource Into Maintenance Mode).

16.3 Preparing and Finishing Maintenance Work

Warning
Warning: Risk of Data Loss

If you need to do testing or maintenance work, follow the general steps below.

Otherwise you risk unwanted side effects, like resources not starting in an orderly fashion, unsynchronized CIBs across the cluster nodes, or even data loss.

  1. Before you start, choose which of the options outlined in Section 16.2 is appropriate for your situation.

  2. Apply this option with Hawk2 or crmsh.

  3. Execute your maintenance task or tests.

  4. After you have finished, put the resource, node or cluster back to normal operation.

16.4 Putting the Cluster Into Maintenance Mode

To put the cluster into maintenance mode on the crm shell, use the following command:

root # crm configure property maintenance-mode=true

To put the cluster back into normal mode after your maintenance work is done, use the following command:

root # crm configure property maintenance-mode=false
Procedure 16.2: Putting the Cluster Into Maintenance Mode with Hawk2
  1. Start a Web browser and log in to the cluster as described in Section 7.2, “Logging In”.

  2. In the left navigation bar, select Cluster Configuration.

  3. In the CRM Configuration group, select the maintenance-mode attribute from the empty drop-down box and click the plus icon to add it.

  4. To set maintenance-mode=true, activate the check box next to maintenance-mode and confirm your changes.

  5. After you have finished the maintenance task for the whole cluster, deactivate the check box next to the maintenance-mode attribute.

    From this point on, High Availability Extension will take over cluster management again.

16.5 Putting a Node Into Maintenance Mode

To put a node into maintenance mode on the crm shell, use the following command:

root # crm node maintenance NODENAME

To put the node back into normal mode after your maintenance work is done, use the following command:

root # crm node ready NODENAME
Procedure 16.3: Putting a Node Into Maintenance Mode with Hawk2
  1. Start a Web browser and log in to the cluster as described in Section 7.2, “Logging In”.

  2. In the left navigation bar, select Cluster Status.

  3. In one of the individual nodes' views, click the wrench icon next to the node and select Maintenance.

  4. After you have finished your maintenance task, click the wrench icon next to the node and select Ready.

16.6 Putting a Node Into Standby Mode

To put a node into standby mode on the crm shell, use the following command:

root # crm node standby NODENAME

To bring the node back online after your maintenance work is done, use the following command:

root # crm node online NODENAME
Procedure 16.4: Putting a Node Into Standby Mode with Hawk2
  1. Start a Web browser and log in to the cluster as described in Section 7.2, “Logging In”.

  2. In the left navigation bar, select Cluster Status.

  3. In one of the individual nodes' views, click the wrench icon next to the node and select Standby.

  4. Finish the maintenance task for the node.

  5. To deactivate the standby mode, click the wrench icon next to the node and select Ready.

16.7 Putting a Resource Into Maintenance Mode

To put a resource into maintenance mode on the crm shell, use the following command:

root # crm resource maintenance RESOURCE_ID true

To put the resource back into normal mode after your maintenance work is done, use the following command:

root # crm resource maintenance RESOURCE_ID false
Procedure 16.5: Putting a Resource Into Maintenance Mode with Hawk2
  1. Start a Web browser and log in to the cluster as described in Section 7.2, “Logging In”.

  2. In the left navigation bar, select Resources.

  3. Select the resource you want to put in maintenance mode or unmanaged mode, click the wrench icon next to the resource and select Edit Resource.

  4. Open the Meta Attributes category.

  5. From the empty drop-down list, select the maintenance attribute and click the plus icon to add it.

  6. Activate the check box next to maintenance to set the maintenance attribute to yes.

  7. Confirm your changes.

  8. After you have finished the maintenance task for that resource, deactivate the check box next to the maintenance attribute for that resource.

    From this point on, the resource will be managed by the High Availability Extension software again.

16.8 Putting a Resource Into Unmanaged Mode

To put a resource into unmanaged mode on the crm shell, use the following command:

root # crm resource unmanage RESOURCE_ID

To put it into managed mode again after your maintenance work is done, use the following command:

root # crm resource manage RESOURCE_ID
Procedure 16.6: Putting a Resource Into Unmanaged Mode with Hawk2
  1. Start a Web browser and log in to the cluster as described in Section 7.2, “Logging In”.

  2. From the left navigation bar, select Status and go to the Resources list.

  3. In the Operations column, click the arrow down icon next to the resource you want to modify and select Edit.

    The resource configuration screen opens.

  4. Below Meta Attributes, select the is-managed entry from the empty drop-down box.

  5. Set its value to No and click Apply.

  6. After you have finished your maintenance task, set is-managed to Yes (which is the default value) and apply your changes.

    From this point on, the resource will be managed by the High Availability Extension software again.

16.9 Rebooting a Cluster Node While In Maintenance Mode

Note
Note: Implications

If the cluster or a node is in maintenance mode, you can stop or restart cluster resources at will—the High Availability Extension will not attempt to restart them. If you stop the Pacemaker service on a node, all daemons and processes (originally started as Pacemaker-managed cluster resources) will continue to run.

If you attempt to start Pacemaker services on a node while the cluster or node is in maintenance mode, Pacemaker will initiate a single one-shot monitor operation (a probe) for every resource to evaluate which resources are currently running on that node. However, it will take no further action other than determining the resources' status.

If you want to take down a node while either the cluster or the node is in maintenance mode, proceed as follows:

  1. On the node you want to reboot or shut down, log in as root or equivalent.

  2. If you have a DLM resource (or other resources depending on DLM), make sure to explicitly stop those resources before stopping the Pacemaker service:

    crm(live)resource# stop RESOURCE_ID

    The reason is that stopping Pacemaker also stops the Corosync service, on whose membership and messaging services DLM depends. If Corosync stops, the DLM resource will assume a split-brain scenario and trigger a fencing operation.

  3. Stop the Pacemaker service on that node:

    root # systemctl stop pacemaker.service
  4. Shut down or reboot the node.

Part III Storage and Data Replication

17 Distributed Lock Manager (DLM)

The Distributed Lock Manager (DLM) in the kernel is the base component used by OCFS2, GFS2, Cluster MD, and cLVM to provide active-active storage at each respective layer.

18 OCFS2

Oracle Cluster File System 2 (OCFS2) is a general-purpose journaling file system that has been fully integrated since the Linux 2.6 Kernel. OCFS2 allows you to store application binary files, data files, and databases on devices on shared storage. All nodes in a cluster have concurrent read and write access to the file system. A user-space control daemon, managed via a clone resource, provides the integration with the HA stack, in particular with Corosync and the Distributed Lock Manager (DLM).

19 GFS2

Global File System 2 or GFS2 is a shared disk file system for Linux computer clusters. GFS2 allows all nodes to have direct concurrent access to the same shared block storage. GFS2 has no disconnected operating-mode, and no client or server roles. All nodes in a GFS2 cluster function as peers. GFS2 supports up to 32 cluster nodes. Using GFS2 in a cluster requires hardware to allow access to the shared storage, and a lock manager to control access to the storage.

SUSE recommends OCFS2 over GFS2 for your cluster environments if performance is one of your major requirements. Our tests have revealed that OCFS2 performs better as compared to GFS2 in such settings.

20 DRBD

The distributed replicated block device (DRBD*) allows you to create a mirror of two block devices that are located at two different sites across an IP network. When used with Corosync, DRBD supports distributed high-availability Linux clusters. This chapter shows you how to install and set up DRBD.

21 Cluster Logical Volume Manager (cLVM)

When managing shared storage on a cluster, every node must be informed about changes that are done to the storage subsystem. The Logical Volume Manager 2 (LVM2), which is widely used to manage local storage, has been extended to support transparent management of volume groups across the whole cluster. Clustered volume groups can be managed using the same commands as local storage.

22 Cluster Multi-device (Cluster MD)

The cluster multi-device (Cluster MD) is a software based RAID storage solution for a cluster. Cluster MD provides the redundancy of RAID1 mirroring to the cluster. Currently, only RAID1 is supported now. This chapter shows you how to create and use Cluster MD.

23 Samba Clustering

A clustered Samba server provides a High Availability solution in your heterogeneous networks. This chapter explains some background information and how to set up a clustered Samba server.

24 Disaster Recovery with Rear (Relax-and-Recover)

Relax-and-Recover (ReaR, in this chapter abbreviated as Rear) is a disaster recovery framework for use by system administrators. It is a collection of Bash scripts that need to be adjusted to the specific production environment that is to be protected in case of disaster.

No disaster recovery solution will work out-of-the-box. Therefore it is essential to take preparations before any disaster happens.

17 Distributed Lock Manager (DLM)

Abstract

The Distributed Lock Manager (DLM) in the kernel is the base component used by OCFS2, GFS2, Cluster MD, and cLVM to provide active-active storage at each respective layer.

17.1 Protocols for DLM Communication

To avoid single points of failure, redundant communication paths are important for High Availability clusters. This is also true for DLM communication. If network bonding (Link Aggregation Control Protocol, LACP) cannot be used for any reason, we highly recommend to define a redundant communication channel (a second ring) in Corosync. For details, see Procedure 4.3, “Defining a Redundant Communication Channel”.

Depending on the configuration in /etc/corosync/corosync.conf, DLM then decides if to use the TCP or SCTP protocol for its communication:

  • If rrp_mode is set to none (which means redundant ring configuration is disabled), DLM automatically uses TCP. However, without a redundant communication channel, DLM communication will fail in case the TCP link is down.

  • If rrp_mode is set to passive (which is the typical setting), and a second communication ring in /etc/corosync/corosync.conf is configured correctly, DLM automatically uses SCTP. In this case, DLM messaging has the redundancy capability provided by SCTP.

17.2 Configuring DLM Cluster Resources

DLM uses the cluster membership services from Pacemaker which run in user space. Therefore, DLM needs to be configured as clone resource that is present on each node in the cluster.

Note
Note: DLM Resource for Several Solutions

As OCFS2, GFS2, Cluster MD, and cLVM all use DLM, it is enough to configure one resource for DLM. As the DLM resource runs on all nodes in the cluster it is configured as a clone resource.

If you have a setup that includes both OCFS2 and cLVM, configuring one DLM resource for both OCFS2 and cLVM is enough.

Procedure 17.1: Configuring a Base Group for DLM

The configuration consists of a base group that includes several primitives and a base clone. Both base group and base clone can be used in various scenarios afterward (for both OCFS2 and cLVM;, for example). You only need to extended the base group with the respective primitives as needed. As the base group has internal colocation and ordering, this simplifies the overall setup as you do not need to specify several individual groups, clones and their dependencies.

Follow the steps below on one node in the cluster:

  1. Start a shell and log in as root or equivalent.

  2. Run crm configure.

  3. Enter the following to create the primitive resource for DLM:

    crm(live)configure# primitive dlm ocf:pacemaker:controld \
      op monitor interval="60" timeout="60"
  4. Create a base group for the DLM resource and further storage-related resources:

    crm(live)configure# group g-storage dlm
  5. Clone the g-storage group so that it runs on all nodes:

    crm(live)configure#  clone cl-storage g-storage \
      meta interleave=true target-role=Started
  6. Review your changes with show.

  7. If everything is correct, submit your changes with commit and leave the crm live configuration with exit.

Note
Note: Failure When Disabling STONITH

Clusters without STONITH are not supported. If you set the global cluster option stonith-enabled to false for testing or troubleshooting purposes, the DLM resource and all services depending on it (such as cLVM, GFS2, and OCFS2) will fail to start.

18 OCFS2

Abstract

Oracle Cluster File System 2 (OCFS2) is a general-purpose journaling file system that has been fully integrated since the Linux 2.6 Kernel. OCFS2 allows you to store application binary files, data files, and databases on devices on shared storage. All nodes in a cluster have concurrent read and write access to the file system. A user-space control daemon, managed via a clone resource, provides the integration with the HA stack, in particular with Corosync and the Distributed Lock Manager (DLM).

18.1 Features and Benefits

OCFS2 can be used for the following storage solutions for example:

  • General applications and workloads.

  • Xen image store in a cluster. Xen virtual machines and virtual servers can be stored on OCFS2 volumes that are mounted by cluster servers. This provides quick and easy portability of Xen virtual machines between servers.

  • LAMP (Linux, Apache, MySQL, and PHP | Perl | Python) stacks.

As a high-performance, symmetric and parallel cluster file system, OCFS2 supports the following functions:

  • An application's files are available to all nodes in the cluster. Users simply install it once on an OCFS2 volume in the cluster.

  • All nodes can concurrently read and write directly to storage via the standard file system interface, enabling easy management of applications that run across the cluster.

  • File access is coordinated through DLM. DLM control is good for most cases, but an application's design might limit scalability if it contends with the DLM to coordinate file access.

  • Storage backup functionality is available on all back-end storage. An image of the shared application files can be easily created, which can help provide effective disaster recovery.

OCFS2 also provides the following capabilities:

  • Metadata caching.

  • Metadata journaling.

  • Cross-node file data consistency.

  • Support for multiple-block sizes up to 4 KB, cluster sizes up to 1 MB, for a maximum volume size of 4 PB (Petabyte).

  • Support for up to 32 cluster nodes.

  • Asynchronous and direct I/O support for database files for improved database performance.

Note
Note: Support for OCFS2

OCFS2 is only supported by SUSE when used with the pcmk (Pacemaker) stack, as provided by SUSE Linux Enterprise High Availability Extension. SUSE does not provide support for OCFS2 in combination with the o2cb stack.

18.2 OCFS2 Packages and Management Utilities

The OCFS2 Kernel module (ocfs2) is installed automatically in the High Availability Extension on SUSE® Linux Enterprise Server 12 SP3. To use OCFS2, make sure the following packages are installed on each node in the cluster: ocfs2-tools and the matching ocfs2-kmp-* packages for your Kernel.

The ocfs2-tools package provides the following utilities for management of OFS2 volumes. For syntax information, see their man pages.

Table 18.1: OCFS2 Utilities

OCFS2 Utility

Description

debugfs.ocfs2

Examines the state of the OCFS file system for the purpose of debugging.

fsck.ocfs2

Checks the file system for errors and optionally repairs errors.

mkfs.ocfs2

Creates an OCFS2 file system on a device, usually a partition on a shared physical or logical disk.

mounted.ocfs2

Detects and lists all OCFS2 volumes on a clustered system. Detects and lists all nodes on the system that have mounted an OCFS2 device or lists all OCFS2 devices.

tunefs.ocfs2

Changes OCFS2 file system parameters, including the volume label, number of node slots, journal size for all node slots, and volume size.

18.3 Configuring OCFS2 Services and a STONITH Resource

Before you can create OCFS2 volumes, you must configure the following resources as services in the cluster: DLM and a STONITH resource.

The following procedure uses the crm shell to configure the cluster resources. Alternatively, you can also use Hawk2 to configure the resources as described in Section 18.6, “Configuring OCFS2 Resources With Hawk2”.

Procedure 18.1: Configuring a STONITH Resource
Note
Note: STONITH Device Needed

You need to configure a fencing device. Without a STONITH mechanism (like external/sbd) in place the configuration will fail.

  1. Start a shell and log in as root or equivalent.

  2. Create an SBD partition as described in Procedure 11.3, “Initializing the SBD Devices”.

  3. Run crm configure.

  4. Configure external/sbd as fencing device with /dev/sdb2 being a dedicated partition on the shared storage for heartbeating and fencing:

    crm(live)configure# primitive sbd_stonith stonith:external/sbd \
      params pcmk_delay_max=30 meta target-role="Started"
  5. Review your changes with show.

  6. If everything is correct, submit your changes with commit and leave the crm live configuration with exit.

For details on configuring the resource group for DLM, see Procedure 17.1, “Configuring a Base Group for DLM”.

18.4 Creating OCFS2 Volumes

After you have configured a DLM cluster resource as described in Section 18.3, “Configuring OCFS2 Services and a STONITH Resource”, configure your system to use OCFS2 and create OCFs2 volumes.

Note
Note: OCFS2 Volumes for Application and Data Files

We recommend that you generally store application files and data files on different OCFS2 volumes. If your application volumes and data volumes have different requirements for mounting, it is mandatory to store them on different volumes.

Before you begin, prepare the block devices you plan to use for your OCFS2 volumes. Leave the devices as free space.

Then create and format the OCFS2 volume with the mkfs.ocfs2 as described in Procedure 18.2, “Creating and Formatting an OCFS2 Volume”. The most important parameters for the command are listed in Table 18.2, “Important OCFS2 Parameters”. For more information and the command syntax, refer to the mkfs.ocfs2 man page.

Table 18.2: Important OCFS2 Parameters

OCFS2 Parameter

Description and Recommendation

Volume Label (-L)

A descriptive name for the volume to make it uniquely identifiable when it is mounted on different nodes. Use the tunefs.ocfs2 utility to modify the label as needed.

Cluster Size (-C)

Cluster size is the smallest unit of space allocated to a file to hold the data. For the available options and recommendations, refer to the mkfs.ocfs2 man page.

Number of Node Slots (-N)

The maximum number of nodes that can concurrently mount a volume. For each of the nodes, OCFS2 creates separate system files, such as the journals. Nodes that access the volume can be a combination of little-endian architectures (such as x86_64) and big-endian architectures (such as s390x).

Node-specific files are referred to as local files. A node slot number is appended to the local file. For example: journal:0000 belongs to whatever node is assigned to slot number 0.

Set each volume's maximum number of node slots when you create it, according to how many nodes that you expect to concurrently mount the volume. Use the tunefs.ocfs2 utility to increase the number of node slots as needed. Note that the value cannot be decreased.

In case the -N parameter is not specified, the number of slots is decided based on the size of the file system.

Block Size (-b)

The smallest unit of space addressable by the file system. Specify the block size when you create the volume. For the available options and recommendations, refer to the mkfs.ocfs2 man page.

Specific Features On/Off (--fs-features)

A comma separated list of feature flags can be provided, and mkfs.ocfs2 will try to create the file system with those features set according to the list. To turn a feature on, include it in the list. To turn a feature off, prepend no to the name.

For an overview of all available flags, refer to the mkfs.ocfs2 man page.

Pre-Defined Features (--fs-feature-level)

Allows you to choose from a set of pre-determined file system features. For the available options, refer to the mkfs.ocfs2 man page.

If you do not specify any features when creating and formatting the volume with mkfs.ocfs2, the following features are enabled by default: backup-super, sparse, inline-data, unwritten, metaecc, indexed-dirs, and xattr.

Procedure 18.2: Creating and Formatting an OCFS2 Volume

Execute the following steps only on one of the cluster nodes.

  1. Open a terminal window and log in as root.

  2. Check if the cluster is online with the command crm status.

  3. Create and format the volume using the mkfs.ocfs2 utility. For information about the syntax for this command, refer to the mkfs.ocfs2 man page.

    For example, to create a new OCFS2 file system on /dev/sdb1 that supports up to 32 cluster nodes, enter the following commands:

    root #  mkfs.ocfs2 -N 32 /dev/sdb1

18.5 Mounting OCFS2 Volumes

You can either mount an OCFS2 volume manually or with the cluster manager, as described in Procedure 18.4, “Mounting an OCFS2 Volume with the Cluster Resource Manager”.

Procedure 18.3: Manually Mounting an OCFS2 Volume
  1. Open a terminal window and log in as root.

  2. Check if the cluster is online with the command crm status.

  3. Mount the volume from the command line, using the mount command.

Warning
Warning: Manually Mounted OCFS2 Devices

If you mount the OCFS2 file system manually for testing purposes, make sure to unmount it again before starting to use it by means of cluster resources.

Procedure 18.4: Mounting an OCFS2 Volume with the Cluster Resource Manager

To mount an OCFS2 volume with the High Availability software, configure an ocfs2 file system resource in the cluster. The following procedure uses the crm shell to configure the cluster resources. Alternatively, you can also use Hawk2 to configure the resources as described in Section 18.6, “Configuring OCFS2 Resources With Hawk2”.

  1. Start a shell and log in as root or equivalent.

  2. Run crm configure.

  3. Configure Pacemaker to mount the OCFS2 file system on every node in the cluster:

    crm(live)configure# primitive ocfs2-1 ocf:heartbeat:Filesystem \
      params device="/dev/sdb1" directory="/mnt/shared" \
      fstype="ocfs2" options="acl" \
      op monitor interval="20" timeout="40" \
      op start timeout="60" op stop timeout="60" \
      meta target-role="Stopped"
  4. Add the ocfs2-1 primitive to the g-storage group you created in Procedure 17.1, “Configuring a Base Group for DLM”.

    crm(live)configure# modgroup g-storage add ocfs2-1

    The add subcommand appends the new group member by default. Because of the base group's internal colocation and ordering, Pacemaker will only start the ocfs2-1 resource on nodes that also have a dlm resource already running.

  5. Review your changes with show.

  6. If everything is correct, submit your changes with commit and leave the crm live configuration with exit.

18.6 Configuring OCFS2 Resources With Hawk2

Instead of configuring the DLM and the file system resource for OCFS2 manually with the crm shell, you can also use the OCFS2 template in Hawk2's Setup Wizard.

Important
Important: Differences Between Manual Configuration and Hawk2

The OCFS2 template in the Setup Wizard does not include the configuration of a STONITH resource. If you use the wizard, you still need to create an SBD partition on the shared storage and configure a STONITH resource as described in Procedure 18.1, “Configuring a STONITH Resource”.

Using the OCFS2 template in the Hawk2 Setup Wizard also leads to a slightly different resource configuration than the manual configuration described in Procedure 17.1, “Configuring a Base Group for DLM” and Procedure 18.4, “Mounting an OCFS2 Volume with the Cluster Resource Manager”.

Procedure 18.5: Configuring OCFS2 Resources with Hawk2's Wizard
  1. Log in to Hawk2:

    https://HAWKSERVER:7630/
  2. In the left navigation bar, select Wizard.

  3. Expand the File System category and select OCFS2 File System.

  4. Follow the instructions on the screen. If you need information about an option, click it to display a short help text in Hawk2. After the last configuration step, Verify the values you have entered.

    The wizard displays the configuration snippet that will be applied to the CIB and any additional changes, if required.

  5. Check the proposed changes. If everything is according to your wishes, apply the changes.

    A message on the screen shows if the action has been successful.

18.7 Using Quotas on OCFS2 File Systems

To use quotas on an OCFS2 file system, create and mount the files system with the appropriate quota features or mount options, respectively: ursquota (quota for individual users) or grpquota (quota for groups). These features can also be enabled later on an unmounted file system using tunefs.ocfs2.

When a file system has the appropriate quota feature enabled, it tracks in its metadata how much space and files each user (or group) uses. Since OCFS2 treats quota information as file system-internal metadata, you do not need to run the quotacheck(8) program. All functionality is built into fsck.ocfs2 and the file system driver itself.

To enable enforcement of limits imposed on each user or group, run quotaon(8) like you would do for any other file system.

For performance reasons each cluster node performs quota accounting locally and synchronizes this information with a common central storage once per 10 seconds. This interval is tuneable with tunefs.ocfs2, options usrquota-sync-interval and grpquota-sync-interval. Therefore quota information may not be exact at all times and as a consequence users or groups can slightly exceed their quota limit when operating on several cluster nodes in parallel.

18.8 For More Information

For more information about OCFS2, see the following links:

https://ocfs2.wiki.kernel.org/

The OCFS2 project home page.

http://oss.oracle.com/projects/ocfs2/

The former OCFS2 project home page at Oracle.

http://oss.oracle.com/projects/ocfs2/documentation

The project's former documentation home page.

19 GFS2

Abstract

Global File System 2 or GFS2 is a shared disk file system for Linux computer clusters. GFS2 allows all nodes to have direct concurrent access to the same shared block storage. GFS2 has no disconnected operating-mode, and no client or server roles. All nodes in a GFS2 cluster function as peers. GFS2 supports up to 32 cluster nodes. Using GFS2 in a cluster requires hardware to allow access to the shared storage, and a lock manager to control access to the storage.

SUSE recommends OCFS2 over GFS2 for your cluster environments if performance is one of your major requirements. Our tests have revealed that OCFS2 performs better as compared to GFS2 in such settings.

19.1 GFS2 Packages and Management Utilities

To use GFS2, make sure gfs2-utils and a matching gfs2-kmp-* package for your Kernel is installed on each node of the cluster.

The gfs2-utils package provides the following utilities for management of GFS2 volumes. For syntax information, see their man pages.

Table 19.1: GFS2 Utilities

GFS2 Utility

Description

fsck.gfs2

Checks the file system for errors and optionally repairs errors.

gfs2_jadd

Adds additional journals to a GFS2 file system.

gfs2_grow

Grow a GFS2 file system.

mkfs.gfs2

Create a GFS2 file system on a device, usually a shared device or partition.

tunegfs2

Allows viewing and manipulating the GFS2 file system parameters such as UUID, label, lockproto and locktable.

19.2 Configuring GFS2 Services and a STONITH Resource

Before you can create GFS2 volumes, you must configure DLM and a STONITH resource.

Procedure 19.1: Configuring a STONITH Resource
Note
Note: STONITH Device Needed

You need to configure a fencing device. Without a STONITH mechanism (like external/sbd) in place the configuration will fail.

  1. Start a shell and log in as root or equivalent.

  2. Create an SBD partition as described in Procedure 11.3, “Initializing the SBD Devices”.

  3. Run crm configure.

  4. Configure external/sbd as fencing device with /dev/sdb2 being a dedicated partition on the shared storage for heartbeating and fencing:

    crm(live)configure# primitive sbd_stonith stonith:external/sbd \
        params pcmk_delay_max=30 meta target-role="Started"
  5. Review your changes with show.

  6. If everything is correct, submit your changes with commit and leave the crm live configuration with exit.

For details on configuring the resource group for DLM, see Procedure 17.1, “Configuring a Base Group for DLM”.

19.3 Creating GFS2 Volumes

After you have configured DLM as cluster resources as described in Section 19.2, “Configuring GFS2 Services and a STONITH Resource”, configure your system to use GFS2 and create GFS2 volumes.

Note
Note: GFS2 Volumes for Application and Data Files

We recommend that you generally store application files and data files on different GFS2 volumes. If your application volumes and data volumes have different requirements for mounting, it is mandatory to store them on different volumes.

Before you begin, prepare the block devices you plan to use for your GFS2 volumes. Leave the devices as free space.

Then create and format the GFS2 volume with the mkfs.gfs2 as described in Procedure 19.2, “Creating and Formatting a GFS2 Volume”. The most important parameters for the command are listed in Table 19.2, “Important GFS2 Parameters”. For more information and the command syntax, refer to the mkfs.gfs2 man page.

Table 19.2: Important GFS2 Parameters

GFS2 Parameter

Description and Recommendation

Lock Protocol Name (-p)

The name of the locking protocol to use. Acceptable locking protocols are lock_dlm (for shared storage) or if you are using GFS2 as a local file system (1 node only), you can specify the lock_nolock protocol. If this option is not specified, lock_dlm protocol will be assumed.

Lock Table Name (-t)

The lock table field appropriate to the lock module you are using. It is clustername:fsname. clustername must match that in the cluster configuration file, /etc/corosync/corosync.conf. Only members of this cluster are permitted to use this file system. fsname is a unique file system name used to distinguish this GFS2 file system from others created (1 to 16 characters).

Number of Journals (-j)

The number of journals for gfs2_mkfs to create. You need at least one journal per machine that will mount the file system. If this option is not specified, one journal will be created.

Procedure 19.2: Creating and Formatting a GFS2 Volume

Execute the following steps only on one of the cluster nodes.

  1. Open a terminal window and log in as root.

  2. Check if the cluster is online with the command crm status.

  3. Create and format the volume using the mkfs.gfs2 utility. For information about the syntax for this command, refer to the mkfs.gfs2 man page.

    For example, to create a new GFS2 file system on /dev/sdb1 that supports up to 32 cluster nodes, use the following command:

    root # mkfs.gfs2 -t hacluster:mygfs2 -p lock_dlm -j 32 /dev/sdb1

    The hacluster name relates to the entry cluster_name in the file /etc/corosync/corosync.conf (this is the default).

19.4 Mounting GFS2 Volumes

You can either mount a GFS2 volume manually or with the cluster manager, as described in Procedure 19.4, “Mounting a GFS2 Volume with the Cluster Manager”.

Procedure 19.3: Manually Mounting a GFS2 Volume
  1. Open a terminal window and log in as root.

  2. Check if the cluster is online with the command crm status.

  3. Mount the volume from the command line, using the mount command.

Warning
Warning: Manually Mounted GFS2 Devices

If you mount the GFS2 file system manually for testing purposes, make sure to unmount it again before starting to use it by means of cluster resources.

Procedure 19.4: Mounting a GFS2 Volume with the Cluster Manager

To mount a GFS2 volume with the High Availability software, configure an OCF file system resource in the cluster. The following procedure uses the crm shell to configure the cluster resources. Alternatively, you can also use Hawk2 to configure the resources.

  1. Start a shell and log in as root or equivalent.

  2. Run crm configure.

  3. Configure Pacemaker to mount the GFS2 file system on every node in the cluster:

    crm(live)configure# primitive gfs2-1 ocf:heartbeat:Filesystem \
      params device="/dev/sdb1" directory="/mnt/shared" fstype="gfs2" \
      op monitor interval="20" timeout="40" \
      op start timeout="60" op stop timeout="60" \
      meta target-role="Stopped"
  4. Create a base group that consists of the dlm primitive you created in Procedure 17.1, “Configuring a Base Group for DLM” and the gfs2-1 primitive. Clone the group:

    crm(live)configure# group g-storage dlm  gfs2-1
         clone cl-storage g-storage \
         meta interleave="true"

    Because of the base group's internal colocation and ordering, Pacemaker will only start the gfs2-1 resource on nodes that also have a dlm resource already running.

  5. Review your changes with show.

  6. If everything is correct, submit your changes with commit and leave the crm live configuration with exit.

20 DRBD

Abstract

The distributed replicated block device (DRBD*) allows you to create a mirror of two block devices that are located at two different sites across an IP network. When used with Corosync, DRBD supports distributed high-availability Linux clusters. This chapter shows you how to install and set up DRBD.

20.1 Conceptual Overview

DRBD replicates data on the primary device to the secondary device in a way that ensures that both copies of the data remain identical. Think of it as a networked RAID 1. It mirrors data in real-time, so its replication occurs continuously. Applications do not need to know that in fact their data is stored on different disks.

DRBD is a Linux Kernel module and sits between the I/O scheduler at the lower end and the file system at the upper end, see Figure 20.1, “Position of DRBD within Linux”. To communicate with DRBD, users use the high-level command drbdadm. For maximum flexibility DRBD comes with the low-level tool drbdsetup.

Position of DRBD within Linux
Figure 20.1: Position of DRBD within Linux
Important
Important: Unencrypted Data

The data traffic between mirrors is not encrypted. For secure data exchange, you should deploy a Virtual Private Network (VPN) solution for the connection.

DRBD allows you to use any block device supported by Linux, usually:

  • partition or complete hard disk

  • software RAID

  • Logical Volume Manager (LVM)

  • Enterprise Volume Management System (EVMS)

By default, DRBD uses the TCP ports 7788 and higher for communication between DRBD nodes. Make sure that your firewall does not prevent communication on the used ports.

You must set up the DRBD devices before creating file systems on them. Everything pertaining to user data should be done solely via the /dev/drbdN device and not on the raw device, as DRBD uses the last part of the raw device for metadata. Using the raw device will cause inconsistent data.

With udev integration, you will also get symbolic links in the form /dev/drbd/by-res/RESOURCES which are easier to use and provide safety against misremembering the devices' minor number.

For example, if the raw device is 1024 MB in size, the DRBD device has only 1023 MB available for data, with about 70 KB hidden and reserved for the metadata. Any attempt to access the remaining kilobytes via raw disks fails because it is not available for user data.

20.2 Installing DRBD Services

Install the High Availability Extension on both SUSE Linux Enterprise Server machines in your networked cluster as described in Part I, “Installation, Setup and Upgrade”. Installing High Availability Extension also installs the DRBD program files.

If you do not need the complete cluster stack but only want to use DRBD, install the packages drbd, drbd-kmp-FLAVOR, drbd-utils, and yast2-drbd.

To simplify the work with drbdadm, use the Bash completion support. If you want to enable it in your current shell session, insert the following command:

root # source /etc/bash_completion.d/drbdadm.sh

To use it permanently for root, create, or extend a file /root/.bashrc and insert the previous line.

20.3 Setting Up DRBD Service

Note
Note: Adjustments Needed

The following procedure uses the server names alice and bob, and the cluster resource name r0. It sets up alice as the primary node and /dev/sda1 for storage. Make sure to modify the instructions to use your own nodes and file names.

The following sections assumes you have two nodes, alice and bob, and that they should use the TCP port 7788. Make sure this port is open in your firewall.

  1. Prepare your system:

    1. Make sure the block devices in your Linux nodes are ready and partitioned (if needed).

    2. If your disk already contains a file system that you do not need anymore, destroy the file system structure with the following command:

      root # dd if=/dev/zero of=YOUR_DEVICE count=16 bs=1M

      If you have more file systems to destory, repeat this step on all devices you want to include into your DRBD setup.

    3. If the cluster is already using DRBD, put your cluster in maintenance mode:

      root # crm configure property maintenance-mode=true

      If you skip this step when your cluster uses already DRBD, a syntax error in the live configuration will lead to a service shutdown.

      As an alternative, you can also use drbdadm -c FILE to test a configuration file.

  2. Configure DRBD by choosing your method:

  3. If you have configured Csync2 (which should be the default), the DRBD configuration files are already included in the list of files need to be synchronized. To synchronize them, use:

    root # csync2 -xv /etc/drbd.d/

    If you do not have Csync2 (or do not want to use it), copy the DRBD configuration files manually to the other node:

    root # scp /etc/drbd.conf bob:/etc/
    root # scp /etc/drbd.d/*  bob:/etc/drbd.d/
  4. Perform the initial synchronization (see Section 20.3.3, “Initializing and Formatting DRBD Resource”).

  5. Reset the cluster's maintenance mode flag:

    root # crm configure property maintenance-mode=false

20.3.1 Configuring DRBD Manually

Note
Note: Restricted Support of Auto Promote Feature

The DRBD9 feature auto promote can use a clone and file system resource instead of a master/slave connection. When using this feature while a file system is being mounted, DRBD will change to primary mode automatically.

The auto promote feature has currently restricted support. With DRBD 9, SUSE supports the same use cases that were also supported with DRBD 8. Use cases beyond that, such as setups with more than two nodes, are not supported.

To set up DRBD manually, proceed as follows:

Procedure 20.1: Manually Configuring DRBD

Beginning with DRBD version 8.3, the former configuration file is split into separate files, located under the directory /etc/drbd.d/.

  1. Open the file /etc/drbd.d/global_common.conf. It contains already some global, pre-defined values. Go to the startup section and insert these lines:

    startup {
        # wfc-timeout degr-wfc-timeout outdated-wfc-timeout
        # wait-after-sb;
        wfc-timeout 100;
        degr-wfc-timeout 120;
    }

    These options are used to reduce the timeouts when booting, see http://www.drbd.org/users-guide-emb/re-drbdconf.html for more details.

  2. Create the file /etc/drbd.d/r0.res. Change the lines according to your situation and save it:

    resource r0 { 1
      device /dev/drbd0; 2
      disk /dev/sda1; 3
      meta-disk internal; 4
      on alice { 5
        address  192.168.1.10:7788; 6
        node-id 0; 7
      }
      on bob { 5
        address 192.168.1.11:7788; 6
        node-id 1; 7
      }
      disk {
        resync-rate 10M; 8
      }
      connection-mesh { 9
        hosts alice bob;
      }
    }

    1

    DRBD resource name that allows some association to the service that needs them. For example, nfs, http, mysql_0, postgres_wal, etc.

    2

    The device name for DRBD and its minor number.

    In the example above, the minor number 0 is used for DRBD. The udev integration scripts will give you a symbolic link /dev/drbd/by-res/nfs/0. Alternatively, omit the device node name in the configuration and use the following line instead:

    drbd0 minor 0 (/dev/ is optional) or /dev/drbd0

    3

    The raw device that is replicated between nodes. Note, in this example the devices are the same on both nodes. If you need different devices, move the disk parameter into the on host.

    4

    The meta-disk parameter usually contains the value internal, but it is possible to specify an explicit device to hold the meta data. See http://www.drbd.org/users-guide-emb/ch-internals.html#s-metadata for more information.

    5

    The on section states which host this configuration statement applies to.

    6

    The IP address and port number of the respective node. Each resource needs an individual port, usually starting with 7788. Both ports must be the same for a DRBD resource.

    7

    The node ID is required when configuring more than two nodes. It is a unique, non-negative integer to distinguish the different nodes.

    8

    The synchronization rate. Set it to one third of the lower of the disk- and network bandwidth. It only limits the resynchronization, not the replication.

    9

    Defines all nodes of a mesh. The hosts parameter contains all host names that share the same DRBD setup.

  3. Check the syntax of your configuration file(s). If the following command returns an error, verify your files:

    root # drbdadm dump all
  4. Continue with Section 20.3.3, “Initializing and Formatting DRBD Resource”.

20.3.2 Configuring DRBD with YaST

YaST can be used to start with an initial setup of DRBD. After you have created your DRBD setup, you can fine-tune the generated files manually.

However, as soon as you have changed the configuration files, do not use the YaST DRBD module anymore. The DRBD module supports only a limited set of basic configuration. If you use it again, it is very likely that the module will not show your changes.

To set up DRBD with YaST, proceed as follows:

Procedure 20.2: Using YaST to Configure DRBD
  1. Start YaST and select the configuration module High Availability › DRBD. If you already have a DRBD configuration, YaST warns you. YaST will change your configuration and will save your old DRBD configuration files as *.YaSTsave.

  2. Leave the booting flag in Start-up Configuration › Booting as it is (by default it is off); do not change that as Pacemaker manages this service.

  3. If you have a firewall running, enable Open Port in Firewall.

  4. Go to the Resource Configuration entry. Press Add to create a new resource (see Figure 20.2, “Resource Configuration”).

    Resource Configuration
    Figure 20.2: Resource Configuration

    The following parameters need to be set:

    Resource Name

    The name of the DRBD resource (mandatory)

    Name

    The host name of the relevant node

    Address:Port

    The IP address and port number (default 7788) for the respective node

    Device

    The block device path that is used to access the replicated data. If the device contains a minor number, the associated block device is usually named /dev/drbdX, where X is the device minor number. If the device does not contain a minor number, make sure to add minor 0 after the device name.

    Disk

    The raw device that is replicated between both nodes. If you use LVM, insert your LVM device name.

    Meta-disk

    The Meta-disk is either set to the value internal or specifies an explicit device extended by an index to hold the meta data needed by DRBD.

    A real device may also be used for multiple drbd resources. For example, if your Meta-Disk is /dev/sda6[0] for the first resource, you may use /dev/sda6[1] for the second resource. However, there must be at least 128 MB space for each resource available on this disk. The fixed metadata size limits the maximum data size that you can replicate.

    All of these options are explained in the examples in the /usr/share/doc/packages/drbd/drbd.conf file and in the man page of drbd.conf(5).

  5. Click Save.

  6. Click Add to enter the second DRBD resource and finish with Save.

  7. Close the resource configuration with Ok and Finish.

  8. If you use LVM with DRBD, it is necessary to change some options in the LVM configuration file (see the LVM Configuration entry). This change can be done by the YaST DRBD module automatically.

    The disk name of local host for the DRBD resource and the default filter will be rejected in the LVM filter. Only /dev/drbd can be scanned for an LVM device.

    For example, if /dev/sda1 is used as a DRBD disk, the device name will be inserted as the first entry in the LVM filter. If you want to change the filter manually, click the Modify LVM Device Filter Automatically check box.

  9. Save your changes with Finish.

  10. Continue with Section 20.3.3, “Initializing and Formatting DRBD Resource”.

20.3.3 Initializing and Formatting DRBD Resource

After you have prepared your system and configured DRBD, initialize your disk for the first time:

  1. On both nodes (alice and bob), initialize the meta data storage:

    root # drbdadm create-md r0
    root # drbdadm up r0
  2. To shorten the initial resynchronization of your DRBD resource check the following:

    • If the DRBD devices on all nodes have the same data (for example, by destroying the file system structure with the dd command as shown in Section 20.3, “Setting Up DRBD Service”), then skip the initial resynchronization with the following command (on both nodes):

      root # drbdadm new-current-uuid --clear-bitmap r0/0

      The state will be Secondary/Secondary UpToDate/UpToDate

    • Otherwise, proceed with the next step.

  3. On the primary node alice, start the resynchronization process:

    root # drbdadm primary --force r0
  4. Check the status with:

    root # drbdadm status r0
    r0 role:Primary
      disk:UpToDate
      bob role:Secondary
      peer-disk:UpToDate
  5. Create your file system on top of your DRBD device, for example:

    root # mkfs.ext3 /dev/drbd0
  6. Mount the file system and use it:

    root # mount /dev/drbd0 /mnt/

20.4 Migrating from DRBD 8 to DRBD 9

Between DRBD 8 (shipped with SUSE Linux Enterprise High Availability Extension 12 SP1) and DRBD 9 (shipped with SUSE Linux Enterprise High Availability Extension 12 SP2), the metadata format has changed. DRBD 9 does not automatically convert previous metadata files to the new format.

After migrating to 12 SP2 and before starting DRBD, convert the DRBD metadata to the version 9 format manually. To do so, use drbdadm create-md. No configuration needs to be changed.

Note
Note: Restricted Support

With DRBD 9, SUSE supports the same use cases that were also supported with DRBD 8. Use cases beyond that, such as setups with more than two nodes, are not supported.

DRBD 9 will fall back to be compatible with version 8. For three nodes and more, you have to recreate the metadata to use DRBD version 9 specific options.

If you have a stacked DRBD resource, refer also to Section 20.5, “Creating a Stacked DRBD Device” for more information.

To keep your data and allow to add new nodes without recreating new resources, do the following:

  1. Set one node in standby mode.

  2. Update all the DRBD packages on all of your nodes, see Section 20.2, “Installing DRBD Services”.

  3. Add the new node information to your resource configuration:

    • node-id on every on section.

    • connection-mesh section contains all host names in the hosts parameter.

    See the example configuration in Procedure 20.1, “Manually Configuring DRBD”.

  4. Enlarge the space of your DRBD disks when using internal as meta-disk key. Use a device that supports enlarging the space like LVM. As an alternative, change to an external disk for metadata and use meta-disk DEVICE;.

  5. Recreate the metadata based on the new configuration:

    root # drbdadm create-md RESOURCE
  6. Cancel the standby mode.

20.5 Creating a Stacked DRBD Device

A stacked DRBD device contains two other devices of which at least one device is also a DRBD resource. In other words, DRBD adds an additional node on top of an already existing DRBD resource (see Figure 20.3, “Resource Stacking”). Such a replication setup can be used for backup and disaster recovery purposes.

Resource Stacking
Figure 20.3: Resource Stacking

Three-way replication makes use of asynchronous (DRBD protocol A) and synchronous replication (DRBD protocol C). The asynchronous part is used for the stacked resource whereas the synchronous part is used for the backup.

Your production environment uses the stacked device. For example, if you have a DRBD device /dev/drbd0 and a stacked device /dev/drbd10 on top, the file system will be created on /dev/drbd10, see Example 20.1, “Configuration of a Three-Node Stacked DRBD Resource” for more details.

Example 20.1: Configuration of a Three-Node Stacked DRBD Resource
# /etc/drbd.d/r0.res
resource r0 {
  protocol C;
  device    /dev/drbd0;
  disk      /dev/sda1;
  meta-disk internal;

  on amsterdam-alice {
    address    192.168.1.1:7900;
  }

  on amsterdam-bob {
    address    192.168.1.2:7900;
  }
}

resource r0-U {
  protocol A;
  device     /dev/drbd10;

  stacked-on-top-of r0 {
    address    192.168.2.1:7910;
  }

  on berlin-charlie {
    disk       /dev/sda10;
    address    192.168.2.2:7910; # Public IP of the backup node
    meta-disk  internal;
  }
}

20.6 Using Resource-Level Fencing

When a DRBD replication link becomes interrupted, Pacemaker tries to promote the DRBD resource to another node. To prevent Pacemaker from starting a service with outdated data, enable resource-level fencing in the DRBD configuration file as shown in Example 20.2, “Configuration of DRBD with Resource-Level Fencing Using the Cluster Information Base (CIB)”.

Example 20.2: Configuration of DRBD with Resource-Level Fencing Using the Cluster Information Base (CIB)
resource RESOURCE {
  net {
    fencing resource-only;
    # ...
  }
  handlers {
    fence-peer "/usr/lib/drbd/crm-fence-peer.9.sh";
    after-resync-target "/usr/lib/drbd/crm-unfence-peer.9.sh";
    # ...
  }
  ...
}

If the DRBD replication link becomes disconnected, DRBD does the following:

  1. DRBD calls the crm-fence-peer.9.sh script.

  2. The script contacts the cluster manager.

  3. The script determines the Pacemaker resource associated with this DRBD resource.

  4. The script ensures that the DRBD resource no longer gets promoted to any other node. It stays on the currently active one.

  5. If the replication link becomes connected again and DRBD completes its synchronization process, then the constraint is removed. The cluster manager is now free to promote the resource.

20.7 Testing the DRBD Service

If the install and configuration procedures worked as expected, you are ready to run a basic test of the DRBD functionality. This test also helps with understanding how the software works.

  1. Test the DRBD service on alice.

    1. Open a terminal console, then log in as root.

    2. Create a mount point on alice, such as /srv/r0:

      root # mkdir -p /srv/r0
    3. Mount the drbd device:

      root # mount -o rw /dev/drbd0 /srv/r0
    4. Create a file from the primary node:

      root # touch /srv/r0/from_alice
    5. Unmount the disk on alice:

      root # umount /srv/r0
    6. Downgrade the DRBD service on alice by typing the following command on alice:

      root # drbdadm secondary r0
  2. Test the DRBD service on bob.

    1. Open a terminal console, then log in as root on bob.

    2. On bob, promote the DRBD service to primary:

      root # drbdadm primary r0
    3. On bob, check to see if bob is primary:

      root # drbdadm status r0
    4. On bob, create a mount point such as /srv/r0:

      root # mkdir /srv/r0
    5. On bob, mount the DRBD device:

      root # mount -o rw /dev/drbd0 /srv/r0
    6. Verify that the file you created on alice exists:

      root # ls /srv/r0/from_alice

      The /srv/r0/from_alice file should be listed.

  3. If the service is working on both nodes, the DRBD setup is complete.

  4. Set up alice as the primary again.

    1. Dismount the disk on bob by typing the following command on bob:

      root # umount /srv/r0
    2. Downgrade the DRBD service on bob by typing the following command on bob:

      root # drbdadm secondary
    3. On alice, promote the DRBD service to primary:

      root # drbdadm primary
    4. On alice, check to see if alice is primary:

      root # drbdadm status r0
  5. To get the service to automatically start and fail over if the server has a problem, you can set up DRBD as a high availability service with Pacemaker/Corosync. For information about installing and configuring for SUSE Linux Enterprise 12 SP3 see Part II, “Configuration and Administration”.

20.8 Tuning DRBD

There are several ways to tune DRBD:

  1. Use an external disk for your metadata. This might help, at the cost of maintenance ease.

  2. Tune your network connection, by changing the receive and send buffer settings via sysctl.

  3. Change the max-buffers, max-epoch-size or both in the DRBD configuration.

  4. Increase the al-extents value, depending on your IO patterns.

  5. If you have a hardware RAID controller with a BBU (Battery Backup Unit), you might benefit from setting no-disk-flushes, no-disk-barrier and/or no-md-flushes.

  6. Enable read-balancing depending on your workload. See http://blogs.linbit.com/p/256/read-balancing/ for more details.

20.9 Troubleshooting DRBD

The DRBD setup involves many different components and problems may arise from different sources. The following sections cover several common scenarios and recommend various solutions.

20.9.1 Configuration

If the initial DRBD setup does not work as expected, there is probably something wrong with your configuration.

To get information about the configuration:

  1. Open a terminal console, then log in as root.

  2. Test the configuration file by running drbdadm with the -d option. Enter the following command:

    root # drbdadm -d adjust r0

    In a dry run of the adjust option, drbdadm compares the actual configuration of the DRBD resource with your DRBD configuration file, but it does not execute the calls. Review the output to make sure you know the source and cause of any errors.

  3. If there are errors in the /etc/drbd.d/* and drbd.conf files, correct them before continuing.

  4. If the partitions and settings are correct, run drbdadm again without the -d option.

    root # drbdadm adjust r0

    This applies the configuration file to the DRBD resource.

20.9.2 Host Names

For DRBD, host names are case-sensitive (Node0 would be a different host than node0), and compared to the host name as stored in the Kernel (see the uname -n output).

If you have several network devices and want to use a dedicated network device, the host name will likely not resolve to the used IP address. In this case, use the parameter disable-ip-verification.

20.9.3 TCP Port 7788

If your system cannot connect to the peer, this might be a problem with your local firewall. By default, DRBD uses the TCP port 7788 to access the other node. Make sure that this port is accessible on both nodes.

20.9.4 DRBD Devices Broken after Reboot

In cases when DRBD does not know which of the real devices holds the latest data, it changes to a split brain condition. In this case, the respective DRBD subsystems come up as secondary and do not connect to each other. In this case, the following message can be found in the logging data:

Split-Brain detected, dropping connection!

To resolve this situation, enter the following commands on the node which has data to be discarded:

root # drbdadm secondary r0

If the state is in WFconnection, disconnect first:

root # drbdadm disconnect r0

On the node which has the latest data enter the following:

root # drbdadm connect  --discard-my-data r0

That resolves the issue by overwriting one node's data with the peer's data, therefore getting a consistent view on both nodes.

20.10 For More Information

The following open source resources are available for DRBD:

  • The project home page http://www.drbd.org.

  • See Article “Highly Available NFS Storage with DRBD and Pacemaker”.

  • http://clusterlabs.org/wiki/DRBD_HowTo_1.0 by the Linux Pacemaker Cluster Stack Project.

  • The following man pages for DRBD are available in the distribution: drbd(8), drbdmeta(8), drbdsetup(8), drbdadm(8), drbd.conf(5).

  • Find a commented example configuration for DRBD at /usr/share/doc/packages/drbd-utils/drbd.conf.example.

  • Furthermore, for easier storage administration across your cluster, see the recent announcement about the DRBD-Manager at http://blogs.linbit.com/p/666/drbd-manager.

21 Cluster Logical Volume Manager (cLVM)

Abstract

When managing shared storage on a cluster, every node must be informed about changes that are done to the storage subsystem. The Logical Volume Manager 2 (LVM2), which is widely used to manage local storage, has been extended to support transparent management of volume groups across the whole cluster. Clustered volume groups can be managed using the same commands as local storage.

21.1 Conceptual Overview

Clustered LVM is coordinated with different tools:

Distributed Lock Manager (DLM)

Coordinates disk access for cLVM and mediates metadata access through locking.

Logical Volume Manager2 (LVM2)

Enables flexible distribution of one file system over several disks. LVM provides a virtual pool of disk space.

Clustered Logical Volume Manager (cLVM)

Coordinates access to the LVM2 metadata so every node knows about changes. cLVM does not coordinate access to the shared data itself; to enable cLVM to do so, you must configure OCFS2 or other cluster-aware applications on top of the cLVM-managed storage.

21.2 Configuration of cLVM

Depending on your scenario it is possible to create a RAID 1 device with cLVM with the following layers:

Make sure you have fulfilled the following prerequisites:

  • A shared storage device is available, such as provided by a Fibre Channel, FCoE, SCSI, iSCSI SAN, or DRBD*.

  • In case of DRBD, both nodes must be primary (as described in the following procedure).

  • Check if the locking type of LVM2 is cluster-aware. The keyword locking_type in /etc/lvm/lvm.conf must contain the value 3 (the default is 1). Copy the configuration to all nodes, if necessary.

  • Check if the lvmetad daemon is disabled because it cannot work with cLVM. In /etc/lvm/lvm.conf, the keyword use_lvmetad must be set to 0 (the default is 1). Copy the configuration to all nodes, if necessary.

21.2.1 Creating the Cluster Resources

Preparing the cluster for use of cLVM includes the following basic steps:

Procedure 21.1: Creating a DLM Resource
  1. Start a shell and log in as root.

  2. Check the current configuration of the cluster resources:

    root # crm configure show
  3. If you have already configured a DLM resource (and a corresponding base group and base clone), continue with Procedure 21.2, “Configuring DLM, CLVM, and STONITH”.

    Otherwise, configure a DLM resource and a corresponding base group and base clone as described in Procedure 17.1, “Configuring a Base Group for DLM”.

  4. Leave the crm live configuration with exit.

21.2.2 Scenario: Configuring Cmirrord

To track mirror log information in a cluster, the cmirrord daemon is used. Cluster mirrors are not possible without this daemon running.

We assume that /dev/sda and /dev/sdb are the shared storage devices as with DRBD, iSCSI, and others. Replace these with your own device name(s), if necessary. Proceed as follows:

Procedure 21.2: Configuring DLM, CLVM, and STONITH
  1. Create a cluster with at least two nodes as described in Installation and Setup Quick Start.

  2. Configure your cluster to run dlm, clvmd, and STONITH:

    root # crm configure
    crm(live)configure# primitive clvmd ocf:heartbeat:clvm \
            params with_cmirrord=1 \
            op stop interval=0 timeout=100 \
    	       op start interval=0 timeout=90 \
    	       op monitor interval=20 timeout=20
    crm(live)configure# primitive dlm ocf:pacemaker:controld \
            op start timeout="90" \
            op stop timeout="100" \
            op monitor interval="60" timeout="60"
    crm(live)configure# primitive sbd_stonith stonith:external/sbd \
            params pcmk_delay_max=30
    crm(live)configure# group g-storage dlm clvmd
    crm(live)configure# clone cl-storage g-storage \
            meta interleave="true" ordered=true
  3. Leave crmsh with exit and commit your changes.

Continue configuring your disks with Procedure 21.3.

Procedure 21.3: Configuring the Disks for cLVM
  1. Create a clustered volume group (VG):

    root # pvcreate /dev/sda /dev/sdb
    root # vgcreate -cy vg1 /dev/sda /dev/sdb
  2. Create a mirrored-log logical volume (LV) in your cluster:

    root # lvcreate -n lv1 -m1 -l10%VG vg1 --mirrorlog mirrored
  3. Use lvs to show the progress. If the percentage number has reached 100%, the mirrored disk is successfully synchronized.

  4. To test the clustered volume /dev/vg1/lv1, use the following steps:

    1. Read or write to /dev/vg1/lv1.

    2. Deactivate your LV with lvchange -an.

    3. Activate your LV with lvchange -ay.

    4. Use lvconvert to convert a mirrored log to a disk log.

  5. Create a mirrored-log LV in another cluster VG. This is a different volume group from the previous one.

The current cLVM can only handle one physical volume (PV) per mirror side. If one mirror is actually made up of several PVs that need to be concatenated or striped, lvcreate does not understand this. For this reason, lvcreate and cmirrord metadata needs to understand grouping of PVs into one side, effectively supporting RAID10.

To support RAID10 for cmirrord, use the following procedure (assuming that /dev/sda, /dev/sdb, /dev/sdc, and /dev/sdd are the shared storage devices):

  1. Create a volume group (VG):

    root # pvcreate /dev/sda /dev/sdb /dev/sdc /dev/sdd
      Physical volume "/dev/sda" successfully created
      Physical volume "/dev/sdb" successfully created
      Physical volume "/dev/sdc" successfully created
      Physical volume "/dev/sdd" successfully created
    root # vgcreate vgtest /dev/sda /dev/sdb /dev/sdc /dev/sdd
      Clustered volume group "vgtest" successfully created
  2. Open the file /etc/lvm/lvm.conf and go to the section allocation. Set the following line and save the file:

    mirror_logs_require_separate_pvs = 1
  3. Add your tags to your PVs:

    root # pvchange --addtag @a /dev/sda /dev/sdb
    root # pvchange --addtag @b /dev/sdc /dev/sdd

    A tag is an unordered keyword or term assigned to the metadata of a storage object. Tagging allows you to classify collections of LVM storage objects in ways that you find useful by attaching an unordered list of tags to their metadata.

  4. List your tags:

    root # pvs -o pv_name,vg_name,pv_tags /dev/sd{a,b,c,d}

    You should receive this output:

    PV        VG   PV Tags
    /dev/sda  vgtest   a
    /dev/sdb  vgtest   a
    /dev/sdc  vgtest   b
    /dev/sdd  vgtest   b

If you need further information regarding LVM, refer to the SUSE Linux Enterprise Server 12 SP3 Storage Administration Guide, chapter LVM Configuration. It is available from http://www.suse.com/documentation/.

21.2.3 Scenario: cLVM With iSCSI on SANs

The following scenario uses two SAN boxes which export their iSCSI targets to several clients. The general idea is displayed in Figure 21.1, “Setup of iSCSI with cLVM”.

Setup of iSCSI with cLVM
Figure 21.1: Setup of iSCSI with cLVM
Warning
Warning: Data Loss

The following procedures will destroy any data on your disks!

Configure only one SAN box first. Each SAN box needs to export its own iSCSI target. Proceed as follows:

Procedure 21.4: Configuring iSCSI Targets (SAN)
  1. Run YaST and click Network Services › iSCSI LIO Target to start the iSCSI Server module.

  2. If you want to start the iSCSI target whenever your computer is booted, choose When Booting, otherwise choose Manually.

  3. If you have a firewall running, enable Open Port in Firewall.

  4. Switch to the Global tab. If you need authentication enable incoming or outgoing authentication or both. In this example, we select No Authentication.

  5. Add a new iSCSI target:

    1. Switch to the Targets tab.

    2. Click Add.

    3. Enter a target name. The name needs to be formatted like this:

      iqn.DATE.DOMAIN

      For more information about the format, refer to Section 3.2.6.3.1. Type "iqn." (iSCSI Qualified Name) at http://www.ietf.org/rfc/rfc3720.txt.

    4. If you want a more descriptive name, you can change it as long as your identifier is unique for your different targets.

    5. Click Add.

    6. Enter the device name in Path and use a Scsiid.

    7. Click Next twice.

  6. Confirm the warning box with Yes.

  7. Open the configuration file /etc/iscsi/iscsid.conf and change the parameter node.startup to automatic.

Now set up your iSCSI initiators as follows:

Procedure 21.5: Configuring iSCSI Initiators
  1. Run YaST and click Network Services › iSCSI Initiator.

  2. If you want to start the iSCSI initiator whenever your computer is booted, choose When Booting, otherwise set Manually.

  3. Change to the Discovery tab and click the Discovery button.

  4. Add your IP address and your port of your iSCSI target (see Procedure 21.4, “Configuring iSCSI Targets (SAN)”). Normally, you can leave the port as it is and use the default value.

  5. If you use authentication, insert the incoming and outgoing user name and password, otherwise activate No Authentication.

  6. Select Next. The found connections are displayed in the list.

  7. Proceed with Finish.

  8. Open a shell, log in as root.

  9. Test if the iSCSI initiator has been started successfully:

    root # iscsiadm -m discovery -t st -p 192.168.3.100
    192.168.3.100:3260,1 iqn.2010-03.de.jupiter:san1
  10. Establish a session:

    root # iscsiadm -m node -l -p 192.168.3.100 -T iqn.2010-03.de.jupiter:san1
    Logging in to [iface: default, target: iqn.2010-03.de.jupiter:san1, portal: 192.168.3.100,3260]
    Login to [iface: default, target: iqn.2010-03.de.jupiter:san1, portal: 192.168.3.100,3260]: successful

    See the device names with lsscsi:

    ...
    [4:0:0:2]    disk    IET      ...     0     /dev/sdd
    [5:0:0:1]    disk    IET      ...     0     /dev/sde

    Look for entries with IET in their third column. In this case, the devices are /dev/sdd and /dev/sde.

Procedure 21.6: Creating the LVM Volume Groups
  1. Open a root shell on one of the nodes you have run the iSCSI initiator from Procedure 21.5, “Configuring iSCSI Initiators”.

  2. Prepare the physical volume for LVM with the command pvcreate on the disks /dev/sdd and /dev/sde:

    root # pvcreate /dev/sdd
    root # pvcreate /dev/sde
  3. Create the cluster-aware volume group on both disks:

    root # vgcreate --clustered y clustervg /dev/sdd /dev/sde
  4. Create logical volumes as needed:

    root # lvcreate --name clusterlv --size 500M clustervg
  5. Check the physical volume with pvdisplay:

      --- Physical volume ---
          PV Name               /dev/sdd
          VG Name               clustervg
          PV Size               509,88 MB / not usable 1,88 MB
          Allocatable           yes
          PE Size (KByte)       4096
          Total PE              127
          Free PE               127
          Allocated PE          0
          PV UUID               52okH4-nv3z-2AUL-GhAN-8DAZ-GMtU-Xrn9Kh
          
          --- Physical volume ---
          PV Name               /dev/sde
          VG Name               clustervg
          PV Size               509,84 MB / not usable 1,84 MB
          Allocatable           yes
          PE Size (KByte)       4096
          Total PE              127
          Free PE               127
          Allocated PE          0
          PV UUID               Ouj3Xm-AI58-lxB1-mWm2-xn51-agM2-0UuHFC
  6. Check the volume group with vgdisplay:

      --- Volume group ---
          VG Name               clustervg
          System ID
          Format                lvm2
          Metadata Areas        2
          Metadata Sequence No  1
          VG Access             read/write
          VG Status             resizable
          Clustered             yes
          Shared                no
          MAX LV                0
          Cur LV                0
          Open LV               0
          Max PV                0
          Cur PV                2
          Act PV                2
          VG Size               1016,00 MB
          PE Size               4,00 MB
          Total PE              254
          Alloc PE / Size       0 / 0
          Free  PE / Size       254 / 1016,00 MB
          VG UUID               UCyWw8-2jqV-enuT-KH4d-NXQI-JhH3-J24anD

After you have created the volumes and started your resources you should have a new device named /dev/dm-*. It is recommended to use a clustered file system on top of your LVM resource, for example OCFS. For more information, see Chapter 18, OCFS2.

21.2.4 Scenario: cLVM With DRBD

The following scenarios can be used if you have data centers located in different parts of your city, country, or continent.

Procedure 21.7: Creating a Cluster-Aware Volume Group With DRBD
  1. Create a primary/primary DRBD resource:

    1. First, set up a DRBD device as primary/secondary as described in Procedure 20.1, “Manually Configuring DRBD”. Make sure the disk state is up-to-date on both nodes. Check this with drbdadm status.

    2. Add the following options to your configuration file (usually something like /etc/drbd.d/r0.res):

      resource r0 {
        startup {
          become-primary-on both;
        }
      
        net {
           allow-two-primaries;
        }
        ...
      }
    3. Copy the changed configuration file to the other node, for example:

      root # scp /etc/drbd.d/r0.res venus:/etc/drbd.d/
    4. Run the following commands on both nodes:

      root # drbdadm disconnect r0
      root # drbdadm connect r0
      root # drbdadm primary r0
    5. Check the status of your nodes:

      root # drbdadm status r0
  2. Include the clvmd resource as a clone in the pacemaker configuration, and make it depend on the DLM clone resource. See Procedure 21.1, “Creating a DLM Resource” for detailed instructions. Before proceeding, confirm that these resources have started successfully on your cluster. You may use crm status or the Web interface to check the running services.

  3. Prepare the physical volume for LVM with the command pvcreate. For example, on the device /dev/drbd_r0 the command would look like this:

    root # pvcreate /dev/drbd_r0
  4. Create a cluster-aware volume group:

    root # vgcreate --clustered y myclusterfs /dev/drbd_r0
  5. Create logical volumes as needed. You may probably want to change the size of the logical volume. For example, create a 4 GB logical volume with the following command:

    root # lvcreate --name testlv -L 4G myclusterfs
  6. The logical volumes within the VG are now available as file system mounts or raw usage. Ensure that services using them have proper dependencies to collocate them with and order them after the VG has been activated.

After finishing these configuration steps, the LVM2 configuration can be done like on any stand-alone workstation.

21.3 Configuring Eligible LVM2 Devices Explicitly

When several devices seemingly share the same physical volume signature (as can be the case for multipath devices or DRBD), it is recommended to explicitly configure the devices which LVM2 scans for PVs.

For example, if the command vgcreate uses the physical device instead of using the mirrored block device, DRBD will be confused which may result in a split brain condition for DRBD.

To deactivate a single device for LVM2, do the following:

  1. Edit the file /etc/lvm/lvm.conf and search for the line starting with filter.

  2. The patterns there are handled as regular expressions. A leading a means to accept a device pattern to the scan, a leading r rejects the devices that follow the device pattern.

  3. To remove a device named /dev/sdb1, add the following expression to the filter rule:

    "r|^/dev/sdb1$|"

    The complete filter line will look like the following:

    filter = [ "r|^/dev/sdb1$|", "r|/dev/.*/by-path/.*|", "r|/dev/.*/by-id/.*|", "a/.*/" ]

    A filter line, that accepts DRBD and MPIO devices but rejects all other devices would look like this:

    filter = [ "a|/dev/drbd.*|", "a|/dev/.*/by-id/dm-uuid-mpath-.*|", "r/.*/" ]
  4. Write the configuration file and copy it to all cluster nodes.

21.4 For More Information

Thorough information is available from the pacemaker mailing list, available at http://www.clusterlabs.org/wiki/Help:Contents.

The official cLVM FAQ can be found at http://sources.redhat.com/cluster/wiki/FAQ/CLVM.

22 Cluster Multi-device (Cluster MD)

Abstract

The cluster multi-device (Cluster MD) is a software based RAID storage solution for a cluster. Cluster MD provides the redundancy of RAID1 mirroring to the cluster. Currently, only RAID1 is supported now. This chapter shows you how to create and use Cluster MD.

22.1 Conceptual Overview

The Cluster MD provides support for use of RAID1 across a cluster environment. The disks or devices used by Cluster MD are accessed by each node. If one device of the Cluster MD fails, it can be replaced at runtime by another device and it is re-synced to provide the same amount of redundancy. The Cluster MD requires Corosync and Distributed Lock Manager (DLM) for co-ordination and messaging.

A Cluster MD device is not automatically started on boot like the rest of the regular MD devices. A clustered device needs to be started using resource agents to ensure the DLM resource has been started.

22.2 Creating a Clustered MD RAID Device

Requirements
  • A running cluster with pacemaker.

  • A resource agent for DLM (see Procedure 17.1, “Configuring a Base Group for DLM” on how to configure DLM).

  • At least two shared disk devices. You can use an additional device as a spare which will fail over automatically in case of device failure.

  • An installed package cluster-md-kmp-default.

  1. Make sure the DLM resource is up and running on every node of the cluster and check the resource status with the command:

    root # crm_resource -r dlm -W
  2. Create the Cluster MD device:

    • If you do not have an existing normal RAID device, create the Cluster MD device on the node running the DLM resource with the following command:

      root # mdadm --create /dev/md0 --bitmap=clustered \
         --metadata=1.2 --raid-devices=2 --level=mirror /dev/sda /dev/sdb

      As Cluster MD only works with version 1.2 of the metadata, it is recommended to specify the version using the --metadata option. For other useful options, refer to the man page of mdadm. Monitor the progress of the re-sync in /proc/mdstat.

    • If you already have an existing normal RAID, first clear the existing bitmap and then create the clustered bitmap:

      root # mdadm --grow /dev/mdX --bitmap=none
      root # mdadm --grow /dev/mdX --bitmap=clustered
    • Optionally, to create a Cluster MD device with a spare device for automatic failover, run the following command on one cluster node:

      root # mdadm --create /dev/md0 --bitmap=clustered --raid-devices=2 \
            --level=mirror --spare-devices=1 /dev/sda /dev/sdb /dev/sdc --metadata=1.2
  3. Get the UUID and the related md path:

    root # mdadm --detail --scan

    The UUID must match the UUID stored in the superblock. For details on the UUID, refer to the mdadm.conf man page.

  4. Open /etc/mdadm.conf and add the md device name and the devices associated with it. Use the UUID from the previous step:

    DEVICE /dev/sda /dev/sdb
    ARRAY /dev/md0 UUID=1d70f103:49740ef1:af2afce5:fcf6a489
  5. Open Csync2's configuration file /etc/csync2/csync2.cfg and add /etc/mdadm.conf:

    group ha_group
    {
       # ... list of files pruned ...
       include /etc/mdadm.conf
    }

22.3 Configuring a Resource Agent

Configure a CRM resource as follows:

  1. Create a Raid1 primitive:

    crm(live)configure# primitive raider Raid1 \
      params raidconf="/etc/mdadm.conf" raiddev=/dev/md0 \
      force_clones=true \
      op monitor timeout=20s interval=10 \
      op start timeout=20s interval=0 \
      op stop timeout=20s interval=0
  2. Add the raider resource to the base group for storage that you have created for DLM:

    crm(live)configure# modgroup g-storage add raider

    The add sub-command appends the new group member by default.

    If not already done, clone the g-storage group so that it runs on all nodes:

    crm(live)configure# clone cl-storage g-storage \
        meta interleave=true target-role=Started
  3. Review your changes with show.

  4. If everything seems correct, submit your changes with commit.

22.4 Adding a Device

To add a device to an existing, active Cluster MD device, first ensure that the device is visible on each node with the command cat /proc/mdstat. If the device is not visible, the command will fail.

Use the following command on one cluster node:

root # mdadm --manage /dev/md0 --add /dev/sdc

The behavior of the new device added depends on the state of the Cluster MD device:

  • If only one of the mirrored devices is active, the new device becomes the second device of the mirrored devices and a recovery is initiated.

  • If both devices of the Cluster MD device are active, the new added device becomes a spare device.

22.5 Re-adding a Temporarily Failed Device

Quite often the failures are transient and limited to a single node. If any of the nodes encounters a failure during an I/O operation, the device will be marked as failed for the entire cluster.

This could happen, for example, because of a cable failure on one of the nodes. After correcting the problem, you can re-add the device. Only the outdated parts will be synchronized as opposed to synchronizing the entire device by adding a new one.

To re-add the device, run the following command on one cluster node:

root # mdadm --manage /dev/md0 --re-add /dev/sdb

22.6 Removing a Device

Before removing a device at runtime for replacement, do the following:

  1. Make sure the device is failed by introspecting /proc/mdstat. Look for an (F) before the device.

  2. Run the following command on one cluster node to make a device fail:

    root # mdadm --manage /dev/md0 --fail /dev/sda
  3. Remove the failed device using the command on one cluster node:

    root # mdadm --manage /dev/md0 --remove /dev/sda

23 Samba Clustering

Abstract

A clustered Samba server provides a High Availability solution in your heterogeneous networks. This chapter explains some background information and how to set up a clustered Samba server.

23.1 Conceptual Overview

Trivial Database (TDB) has been used by Samba for many years. It allows multiple applications to write simultaneously. To make sure all write operations are successfully performed and do not collide with each other, TDB uses an internal locking mechanism.

Cluster Trivial Database (CTDB) is a small extension of the existing TDB. CTDB is described by the project as a cluster implementation of the TDB database used by Samba and other projects to store temporary data.

Each cluster node runs a local CTDB daemon. Samba communicates with its local CTDB daemon instead of writing directly to its TDB. The daemons exchange metadata over the network, but actual write and read operations are done on a local copy with fast storage. The concept of CTDB is displayed in Figure 23.1, “Structure of a CTDB Cluster”.

Note
Note: CTDB For Samba Only

The current implementation of the CTDB Resource Agent configures CTDB to only manage Samba. Everything else, including IP failover, should be configured with Pacemaker.

CTDB is only supported for completely homogeneous clusters. For example, all nodes in the cluster need to have the same architecture. You cannot mix i586 with x86_64.

Structure of a CTDB Cluster
Figure 23.1: Structure of a CTDB Cluster

A clustered Samba server must share certain data:

  • Mapping table that associates Unix user and group IDs to Windows users and groups.

  • The user database must be synchronized between all nodes.

  • Join information for a member server in a Windows domain must be available on all nodes.

  • Metadata needs to be available on all nodes, like active SMB sessions, share connections, and various locks.

The goal is that a clustered Samba server with N+1 nodes is faster than with only N nodes. One node is not slower than an unclustered Samba server.

23.2 Basic Configuration

Note
Note: Changed Configuration Files

The CTDB Resource Agent automatically changes /etc/sysconfig/ctdb. Use crm ra info CTDB to list all parameters that can be specified for the CTDB resource.

To set up a clustered Samba server, proceed as follows:

Procedure 23.1: Setting Up a Basic Clustered Samba Server
  1. Prepare your cluster:

    1. Make sure the following packages are installed before you proceed: ctdb, tdb-tools, and samba (needed for smb and nmb resources).

    2. Configure your cluster (Pacemaker, OCFS2) as described in this guide in Part II, “Configuration and Administration”.

    3. Configure a shared file system, like OCFS2, and mount it, for example, on /srv/clusterfs. See Chapter 18, OCFS2 for more information.

    4. If you want to turn on POSIX ACLs, enable it:

      • For a new OCFS2 file system use:

        root # mkfs.ocfs2 --fs-features=xattr ...
      • For an existing OCFS2 file system use:

        root # tunefs.ocfs2 --fs-feature=xattr DEVICE

        Make sure the acl option is specified in the file system resource. Use the crm shell as follows:

        crm(live)configure# primitive ocfs2-3 ocf:heartbeat:Filesystem params options="acl" ...
    5. Make sure the services ctdb, smb, and nmb are disabled:

      root # systemctl disable ctdb
      root # systemctl disable smb
      root # systemctl disable nmb
    6. Open port 4379 of your firewall on all nodes. This is needed for CTDB to communicate with other cluster nodes.

  2. Create a directory for the CTDB lock on the shared file system:

    root # mkdir -p /srv/clusterfs/samba/
  3. In /etc/ctdb/nodes insert all nodes which contain all private IP addresses of each node in the cluster:

    192.168.1.10
    192.168.1.11
  4. Configure Samba. Add the following lines in the [global] section of /etc/samba/smb.conf. Use the host name of your choice in place of "CTDB-SERVER" (all nodes in the cluster will appear as one big node with this name, effectively):

    [global]
        # ...
        # settings applicable for all CTDB deployments
        netbios name = CTDB-SERVER
        clustering = yes
        idmap config * : backend = tdb2
        passdb backend = tdbsam
        ctdbd socket = /var/lib/ctdb/ctdb.socket
        # settings necessary for CTDB on OCFS2
        fileid:algorithm = fsid
        vfs objects = fileid
        # ...
  5. Copy the configuration file to all of your nodes by using csync2:

    root # csync2 -xv

    For more information, see Procedure 4.6, “Synchronizing the Configuration Files with Csync2”.

  6. Add a CTDB resource to the cluster:

    root # crm configure
    crm(live)configure# primitive ctdb ocf:heartbeat:CTDB params \
        ctdb_manages_winbind="false" \ 
        ctdb_manages_samba="false" \
        ctdb_recovery_lock="/srv/clusterfs/samba/ctdb.lock" \
        ctdb_socket="/var/lib/ctdb/ctdb.socket" \ 
          op monitor interval="10" timeout="20" \
          op start interval="0" timeout="90" \
          op stop interval="0" timeout="100"
    crm(live)configure# primitive nmb systemd:nmb \
        op start timeout="60" interval="0" \
        op stop timeout="60" interval="0" \
        op monitor interval="60" timeout="60"
    crm(live)configure# primitive smb systemd:smb \
        op start timeout="60" interval="0" \
        op stop timeout="60" interval="0" \
        op monitor interval="60" timeout="60"
    crm(live)configure# group g-ctdb ctdb nmb smb
    crm(live)configure# clone cl-ctdb g-ctdb meta interleave="true"
    crm(live)configure# colocation col-ctdb-with-clusterfs inf: cl-ctdb cl-clusterfs
    crm(live)configure# order o-clusterfs-then-ctdb inf: cl-clusterfs cl-ctdb
    crm(live)configure# commit
  7. Add a clustered IP address:

    crm(live)configure# primitive ip ocf:heartbeat:IPaddr2 params ip=192.168.2.222 \
        unique_clone_address="true" \
        op monitor interval="60" \
        meta resource-stickiness="0"
    crm(live)configure# clone cl-ip ip \
        meta interleave="true" clone-node-max="2" globally-unique="true"
    crm(live)configure# colocation col-ip-with-ctdb 0: cl-ip cl-ctdb
    crm(live)configure# order o-ip-then-ctdb 0: cl-ip cl-ctdb
    crm(live)configure# commit

    If unique_clone_address is set to true, the IPaddr2 resource agent adds a clone ID to the specified address, leading to three different IP addresses. These are usually not needed, but help with load balancing. For further information about this topic, see Section 14.2, “Configuring Load Balancing with Linux Virtual Server”.

  8. Commit your change:

    crm(live)configure# commit
  9. Check the result:

    root # crm status
    Clone Set: cl-storage [dlm]
         Started: [ factory-1 ]
         Stopped: [ factory-0 ]
    Clone Set: cl-clusterfs [clusterfs]
         Started: [ factory-1 ]
         Stopped: [ factory-0 ]
     Clone Set: cl-ctdb [g-ctdb]
         Started: [ factory-1 ]
         Started: [ factory-0 ]
     Clone Set: cl-ip [ip] (unique)
         ip:0       (ocf:heartbeat:IPaddr2):       Started factory-0
         ip:1       (ocf:heartbeat:IPaddr2):       Started factory-1
  10. Test from a client machine. On a Linux client, run the following command to see if you can copy files from and to the system:

    root # smbclient //192.168.2.222/myshare

23.3 Joining an Active Directory Domain

Active Directory (AD) is a directory service for Windows server systems.

The following instructions outline how to join a CTDB cluster to an Active Directory domain:

  1. Create a CTDB resource as described in Procedure 23.1, “Setting Up a Basic Clustered Samba Server”.

  2. Install the samba-winbind package.

  3. Disable the winbind service:

    root # systemctl disable winbind
  4. Define a winbind cluster resource:

    root # crm configure
    crm(live)configure# primitive winbind systemd:winbind \
        op start timeout="60" interval="0" \
        op stop timeout="60" interval="0" \
        op monitor interval="60" timeout="60"
    crm(live)configure# commit
  5. Edit the g-ctdb group and insert winbind between the nmb and smb resources:

    crm(live)configure# edit g-ctdb

    Save and close the editor with :w (vim).

  6. Consult your Windows Server documentation for instructions on how to set up an Active Directory domain. In this example, we use the following parameters:

    AD and DNS server

    win2k3.2k3test.example.com

    AD domain

    2k3test.example.com

    Cluster AD member NetBIOS name

    CTDB-SERVER
  7. Procedure 23.2, “Joining Active Directory”

Finally, join your cluster to the Active Directory server:

Procedure 23.2: Joining Active Directory
  1. Make sure the following files are included in Csync2's configuration to become installed on all cluster hosts:

    /etc/samba/smb.conf
    /etc/security/pam_winbind.conf
    /etc/krb5.conf
    /etc/nsswitch.conf
    /etc/security/pam_mount.conf.xml
    /etc/pam.d/common-session

    You can also use YaST's Configure Csync2 module for this task, see Section 4.5, “Transferring the Configuration to All Nodes”.

  2. Run YaST and open the Windows Domain Membership module from the Network Services entry.

  3. Enter your domain or workgroup settings and finish with Ok.

23.4 Debugging and Testing Clustered Samba

To debug your clustered Samba server, the following tools which operate on different levels are available:

ctdb_diagnostics

Run this tool to diagnose your clustered Samba server. Detailed debug messages should help you track down any problems you might have.

The ctdb_diagnostics command searches for the following files which must be available on all nodes:

/etc/krb5.conf
/etc/hosts
/etc/ctdb/nodes
/etc/sysconfig/ctdb
/etc/resolv.conf
/etc/nsswitch.conf
/etc/sysctl.conf
/etc/samba/smb.conf
/etc/fstab
/etc/multipath.conf
/etc/pam.d/system-auth
/etc/sysconfig/nfs
/etc/exports
/etc/vsftpd/vsftpd.conf

If the files /etc/ctdb/public_addresses and /etc/ctdb/static-routes exist, they will be checked as well.

ping_pong

Check whether your file system is suitable for CTDB with ping_pong. It performs certain tests of your cluster file system like coherence and performance (see http://wiki.samba.org/index.php/Ping_pong) and gives some indication how your cluster may behave under high load.

send_arp Tool and SendArp Resource Agent

The SendArp resource agent is located in /usr/lib/heartbeat/send_arp (or /usr/lib64/heartbeat/send_arp). The send_arp tool sends out a gratuitous ARP (Address Resolution Protocol) packet and can be used for updating other machines' ARP tables. It can help to identify communication problems after a failover process. If you cannot connect to a node or ping it although it shows the clustered IP address for samba, use the send_arp command to test if the nodes only need an ARP table update.

For more information, refer to http://wiki.wireshark.org/Gratuitous_ARP.

To test certain aspects of your cluster file system proceed as follows:

Procedure 23.3: Test Coherence and Performance of Your Cluster File System
  1. Start the command ping_pong on one node and replace the placeholder N with the amount of nodes plus one. The file ABSPATH/data.txt is available in your shared storage and is therefore accessible on all nodes (ABSPATH indicates an absolute path):

    ping_pong ABSPATH/data.txt N

    Expect a very high locking rate as you are running only one node. If the program does not print a locking rate, replace your cluster file system.

  2. Start a second copy of ping_pong on another node with the same parameters.

    Expect to see a dramatic drop in the locking rate. If any of the following applies to your cluster file system, replace it:

    • ping_pong does not print a locking rate per second,

    • the locking rates in the two instances are not almost equal,

    • the locking rate did not drop after you started the second instance.

  3. Start a third copy of ping_pong. Add another node and note how the locking rates change.

  4. Kill the ping_pong commands one after the other. You should observe an increase of the locking rate until you get back to the single node case. If you did not get the expected behavior, find more information in Chapter 18, OCFS2.

24 Disaster Recovery with Rear (Relax-and-Recover)

Abstract

Relax-and-Recover (ReaR, in this chapter abbreviated as Rear) is a disaster recovery framework for use by system administrators. It is a collection of Bash scripts that need to be adjusted to the specific production environment that is to be protected in case of disaster.

No disaster recovery solution will work out-of-the-box. Therefore it is essential to take preparations before any disaster happens.

24.1 Conceptual Overview

The following sections describe the general disaster recovery concept and the basic steps you need to execute for successful recovery with Rear. They also provide some guidance on Rear requirements, some limitations to be aware of, and scenarios and backup tools.

24.1.1 Creating a Disaster Recovery Plan

Before the worst scenario happens, take action: analyze your IT infrastructure for any substantial risks, evaluate your budget, and create a disaster recovery plan. If you do not already have a disaster recovery plan at hand, find some information on each step below:

  • Risk Analysis.  Conduct a solid risk analysis of your infrastructure. List all the possible threats and evaluate how serious they are. Determine how likely these threats are and prioritize them. It is recommended to use a simple categorization: probability and impact.

  • Budget Planning.  The outcome of the analysis is an overview, which risks can be tolerated and which are critical for your business. Ask yourself how you can minimize risks and how much will it cost. Depending on how big your company is, spend two to fifteen percent of the overall IT budget on disaster recovery.

  • Disaster Recovery Plan Development.  Make checklists, test procedures, establish and assign priorities, and inventory your IT infrastructure. Define how to deal with a problem when some services in your infrastructure fail.

  • Test.  After defining an elaborate plan, test it. Test it at least once a year. Use the same testing hardware as your main IT infrastructure.

24.1.2 What Does Disaster Recovery Mean?

If a system in a production environment has been destroyed (for whatever reasons—be it broken hardware, a misconfiguration or software problems), you need to re-create the system. The recreation can be done either on the same hardware or on compatible replacement hardware. Re-creating a system means more than restoring files from a backup. It also includes preparing the system's storage (with regard to partitioning, file systems, and mount points), and reinstalling the boot loader.

24.1.3 How Does Disaster Recovery With Rear Work?

While the system is up and running, create a backup of the files and create a recovery system on a recovery medium. The recovery system contains a recovery installer.

In case the system has been destroyed, replace broken hardware (if needed), boot the recovery system from the recovery medium and launch the recovery installer. The recovery installer re-creates the system: First, it prepares the storage (partitioning, file systems, mount points), then it restores the files from the backup. Finally, it reinstalls the boot loader.

24.1.4 Rear Requirements

To use Rear you need at least two identical systems: the machine that runs your production environment and an identical test machine. Identical in this context means that you can, for example, replace a network card with another one using the same Kernel driver.

Warning
Warning: Identical Drivers Required

If a hardware component does not use the same driver as the one in your production environment, it is not considered identical by Rear.

24.1.5 Rear Version Updates

To be compatible with older service packs, SUSE Linux Enterprise High Availability Extension 12 SP3 ships with three different Rear versions: 1.16 (included in RPM package rear116), 1.17.2.a (rear1172a), and 1.18.a (rear118a). The latest version contains some later enhancements from the upstream GitHub project.

Note
Note: Find Important Information in Changelogs

Any information about bugfixes, incompatibilities, and other issues can be found in the changelogs of the packages. It is recommended to review also later package versions of Rear in case you need to re-validate your disaster recovery procedure.

Be aware of the following issues with Rear:

  • To allow disaster recover on UEFI systems, you need version 1.18.a and the package ebiso. Only this version supports the new helper tool /usr/bin/ebiso. This helper tool is used to create a UEFI-bootable Rear system ISO image.

  • If you have a tested and fully functional disaster recovery procedure with one Rear version, do not update Rear. Keep the Rear package and do not change your disaster recovery method!

  • Version updates for Rear are provided as separate packages that intentionally conflict with each other to prevent your installed version getting accidentally replaced with another version.

In the following cases you need to completely re-validate your existing disaster recovery procedure:

  • For each Rear version update.

  • When you update Rear manually.

  • For each software that is used by Rear.

  • If you update low-level system components such as parted, btrfs and similar.

24.1.6 Limitations with Btrfs

The following limitations apply if you use Btrfs.

Your System Includes Subvolumes, but No Snapshots Subvolumes

At least Rear version 1.17.2.a is required. This version supports re-creating normal Btrfs subvolume structure (no snapshot subvolumes).

Your System Includes Snapshot Subvolumes
Warning
Warning

Btrfs snapshot subvolumes cannot be backed up and restored as usual with file-based backup software.

While recent snapshot subvolumes on Btrfs file systems need almost no disk space (because of Btrfs's copy-on-write functionality), those files would be backed up as complete files when using file-based backup software. They would end up twice in the backup with their original file size. Therefore, it is impossible to restore the snapshots as they have been before on the original system.

Your SLE12 System Needs Matching Rear Configuration

The setup in SLE12 GA, SLE12 SP1, and SLE12 SP2 have several different incompatible Btrfs default structures. As such, it is crucial to use a matching Rear configuration file. See the example files /usr/share/rear/conf/examples/SLE12*-btrfs-example.conf.

24.1.7 Scenarios and Backup Tools

Rear can create a disaster recovery system (including a system-specific recovery installer) that can be booted from a local medium (like a hard disk, a flash disk, a DVD/CD-R) or via PXE. The backup data can be stored on a network file system, for example NFS, as described in Example 24.1.

Rear does not replace a file backup, but complements it. By default, Rear supports the generic tar command, and several third-party backup tools (such as Tivoli Storage Manager, QNetix Galaxy, Symantec NetBackup, EMC NetWorker, or HP DataProtector). Refer to Example 24.2 for an example configuration of using Rear with EMC NetWorker as backup tool.

24.1.8 Basic Steps

For a successful recovery with Rear in case of disaster, you need to execute the following basic steps:

Setting Up Rear and Your Backup Solution

This includes tasks like editing the Rear configuration file, adjusting the Bash scripts, and configuring the backup solution that you want to use.

Creating the Recovery Installation System

While the system to be protected is up and running use the rear mkbackup command to create a file backup and to generate a recovery system that contains a system-specific Rear recovery installer.

Testing the Recovery Process

Whenever you have created a disaster recovery medium with Rear, test the disaster recovery process thoroughly. It is essential to use a test machine that has identical hardware like the one that is part of your production environment. For details, refer to Section 24.1.4, “Rear Requirements”.

Recovering from Disaster

After a disaster has occurred, replace any broken hardware (if necessary). Then boot the Rear recovery system and start the recovery installer with the rear recover command.