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 just 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.