Clustering requires communication between nodes to synchronize the state of running applications or to notify changes in the cluster definition.
JGroups (http://jgroups.org/manual/html/index.html) is a reliable group communication toolkit written entirely in Java. It is based on IP multicast, but extends by providing reliability and group membership.
Member processes of a group can be located on the same host, within the same Local Area Network (LAN), or across a Wide Area Network (WAN). A member can be in turn part of multiple groups.
The following picture illustrates a detailed view of JGroups architecture:
A JGroups process consists basically of three parts, namely the Channel, Building blocks, and the Protocol stack. The Channel is a simple socket-like interface used by application programmers to build reliable group communication applications. Building blocks are an abstraction interface layered on top of Channels, which can be used instead of Channels whenever...