The J2EE Agents can be clustered to provide load balancing and fault tolerance. If the agent where the user's session was established goes down, the user’s request is sent to another agent in the cluster. This agent pulls the user’s session information from the Identity Server. This allows the user to continue accessing resources, without needing to reauthenticate.
A cluster of J2EE Agents must reside behind a Layer 4 (L4) server. Clients access the virtual IP on the L4 , and the L4 alleviates server load by balancing traffic across the cluster of agents. Whenever a user enters the URL for an agent resource, the request is routed to the L4 server, and the L4 routes the user to one of the agents in the cluster, as traffic necessitates.
A cluster is created by assigning one or more agents to a cluster configuration. The agents must all belong to one type. For example, you can have a cluster of WebLogic agents, but not a cluster with both JBoss agents and WebLogic agents.