A server cluster is a set of servers that are managed together and participate in workload management. The servers that are members of a cluster can be on different host machines.
Servers that belong to a cluster are members of that cluster set and must all have identical application components deployed on them. Other than the applications configured to run on them, cluster members do not have to share any other configuration data. One cluster member might be running on a huge multi-processor enterprise server system, while another member of that same cluster might be running on a smaller system. The server configuration settings for each of these two cluster members are very different, except in the area of application components assigned to them. In that area of configuration, they are identical. This allows client work to be distributed across all the members of a cluster instead of all workload being handled by a single application server.
In WebSphere ESB, the support for server clusters is provided by the underlying WebSphere Application Server Network Deployment. The only difference is that you cannot create a cluster from an existing application server as a template.
For more information about server clusters, see the related topics.