Now that you know how the various J2EE services operate in a clustered environment and understand different cluster architectures, let's turn our attention to the network infrastructure needed to support WebLogic clustering. By understanding how WebLogic clusters interact with this infrastructure, you are in a better position to configure and optimize the cluster configuration. WebLogic uses two forms of network communication within a cluster:
WebLogic instances within a cluster use multicast communication to broadcast heartbeats. These heartbeats verify the server's availability to other members of the cluster. The clustered JNDI service also relies on multicast communication to broadcast the availability of cluster-aware objects and services. Thus, multicast communication is vital for both high availability and load balancing.
Socket communication is used in peer-to-peer communication between members of a cluster. This can occur when server-side objects access objects on a peer server, or when session-state information is replicated to a secondary server.
Each server listens for heartbeats broadcast by other servers in the cluster. This enables the server to detect any failure among its peers. In fact, each server broadcasts a unique heartbeat message every 10 seconds. If a server in the cluster misses three heartbeats of a peer, it marks that peer server as failed. Likewise, if a socket is closed unexpectedly by a peer server, the server that initiated the ...