JGroups is a toolkit for reliable multicast communication. It can be used to create groups of processes whose members can send messages to each other. JGroups enables developers to create reliable multipoint (multicast) applications where reliability is a deployment issue. JGroups also relieves the application developer from implementing this logic themselves. This saves significant development time and allows for the application to be deployed in different environments without having to change code.

JGroups Features

• Group creation and deletion. Group members can be spread across LANs or WANs
• Joining and leaving of groups
• Membership detection and notification about joined/left/crashed members
• Detection and removal of crashed members
• Sending and receiving of member-to-group messages (point-to-multipoint)
• Sending and receiving of member-to-member messages (point-to-point)

Flexible Protocol Stack

The most powerful feature of JGroups is its flexible protocol stack, which allows developers to adapt it to exactly match their application requirements and network characteristics. The benefit of this is that you only pay for what you use. By mixing and matching protocols, various differing application requirements can be satisfied. JGroups comes with a number of protocols (but anyone can write their own), for example

• Transport protocols: UDP (IP Multicast), TCP, JMS
• Fragmentation of large messages
• Reliable unicast and multicast message transmission. Lost messages are retransmitted
• Failure detection: crashed members are excluded from the membership
• Ordering protocols: Atomic (all-or-none message delivery), Fifo, Causal, Total Order (sequencer or token based)
• Membership
• Encryption

Documentation

Since JGroups is a key component of JBoss AS clustering and caching, you should review the JBoss AS documentation for details beyond the documentation outlined below which is mostly intended for those interested in using JGroups standalone.

• JGroups Overview
• JGroups FAQ
• JGroups API Overview
• JGroups Building Blocks
• JGroups Manual
• JGroups 2.x Javadoc
• JGroups Wiki