Unexpected ERS Cluster Resource Failure post ASCS Failover in SAP NetWeaver ENSA1 Architecture
This document (000021333) is provided subject to the disclaimer at the end of this document.
SUSE Linux Enterprise Server for SAP Applications 15 SP4
SUSE Linux Enterprise Server for SAP Applications 15 SP3
SUSE Linux Enterprise Server for SAP Applications 15 SP2
SUSE Linux Enterprise Server for SAP Applications 12 SP5
# sapcontrol -nr 10 -function HAFailoverToNode "node_name"
Following the manual relocation of the ASCS instance and the successful loading of the ENQ Lock Table from the ERS instance, the ERS cluster resource encountered a cluster monitor operation failure. This event is evidenced both in the system logs and by the output from the "crm_mon -1r" command:
# /usr/sbin/crm_mon -r -1 Failed Resource Actions: * rsc_sap_SY1_ERS11_monitor_11000 on cl1-sap-02-vm 'not running' (7): call=128, status='complete', last-rc-change='Wed Nov 15 08:41:59 2023', queued=0ms, exec=0ms
# crm resource refresh rsc_sap_SY1_ERS11
ASCS, after failover to the node where ERS is running: dev_enqsrv
[Thr 140394463781248] Mon Nov 7 12:16:56 2023 [Thr 140394463781248] LOG GEZ=> Server start [encllog.cpp 550] [Thr 140394463781248] Enqueue server start with instance number 00
ERS, after ASCS migration to its node: dev_enrepsrv.old
[Thr 139839211409792] Mon Nov 7 12:17:00 2023 [Thr 139839211409792] EnEnqToRep::checkEnserverAttached: the enqueue server has attached to the replicationtable [Thr 139839211409792] checkActive: Enqueue server has attached my repl. table [Thr 139839211409792] checkActive: shutdown ...
From the perspective of an ENSA1 NW cluster, this behavior might be viewed as a cosmetic issue. Once the ASCS failover occurs and the lock table attachment is complete, the ERS instance will stop and be restarted on the other node by the cluster (previously hosting the ASCS resource group). This is a standard operational sequence within the ENSA1 high-availability cluster approach.
Contrary to the behavior observed in the ENSA1 approach, the newer ENSA2 architecture, employing both Enqueue Server version 2 and Enqueue Replicator Server version 2, introduces significant resilience and flexibility. This is achieved by replicating the ENQ Lock Table via network instead of local shared memory. In the ENSA2 approach, ERS instance does not stop after successful replication/export of the Lock Table. Moreover, the ASCS instance doesn't have to relocate to the ERS node for attaching the Lock Table; it can recover on its original node and receive the ENQ Lock Table through the network.
The ENSA2 cluster approach is applicable starting from SAP NW 7.52 and later versions, which include support for Standalone Enqueue Server 2 with integrated replication support through Enqueue Replicator 2. Similarly, from S/4HANA ABAP Platform 1809 onwards, Standalone Enqueue Server 2 and Enqueue Replicator 2 are installed by default for high-availability scenarios.
For guidance on implementing ENSA2 in high-availability setups, using SAP NW 7.52 and later, the following Best Practice Guide is recommended. Although primarily focused on S/4HANA ABAP Platform 1809, this guide is universally applicable to any SAP product or stack that supports both Enqueue Server 2 and Enqueue Replication Server 2. This is due to the SUSE cluster stack's capability to independently manage ASCS and ERS components, regardless of the specific stack they are utilized in. This guide is relevant for SAP NW 7.52 and newer versions:
SAP S/4 HANA - Enqueue Replication 2 High Availability Cluster
For SAP NW 7.51 and earlier versions, it's important to note that, according to "SAP Note 2630416 - Support for Standalone Enqueue Server 2", these versions do not support the new Standalone Enqueue Server 2 (ENSA2) in high-availability (HA) setups. This is because SAP NW 7.51 and its predecessors continue to operate with the older Enqueue Replication Server. Therefore, for SAP NW 7.51 and earlier versions, the ENSA1 cluster architecture should be used:
SAP NetWeaver Enqueue Replication 1 High Availability Cluster
An alternative new approach for managing a high-availability stack for SAP NW 7.52 (ENSA2) can be implemented using the following guide:
SAP S/4 HANA - Enqueue Replication 2 High Availability Cluster With Simple Mount
Moreover, for scenarios involving a Multi-SID setups in one cluster, the following guide offers examples for both ENSA1 and ENSA2 configurations:
SAP S/4HANA and SAP NetWeaver Multi-SID Cluster Guide
Related SAP Acronyms:
ABAP Application server ASCS ABAP Central Services (Message server & Enqueue Server) ENSA1 Standalone Enqueue Server 1 ENSA2 Standalone Enqueue Server 2 ERS Enqueue replication Server ERS2 Enqueue replication Server 2 NW NetWeaver
This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.
- Document ID:000021333
- Creation Date: 26-Jan-2024
- Modified Date:26-Jan-2024
- SUSE Linux Enterprise Server for SAP Applications
For questions or concerns with the SUSE Knowledgebase please contact: tidfeedback[at]suse.com