2.5. Message Broker

Messages can be sent directly between two applications, but this requires the two applications to know about each other when they are written; it also means that both applications need to be online at the same time and producing and consuming data at the same rate to communicate. This hard-wiring of communication between applications does not scale as more and more applications become interested in the information being shared.

A message broker provides a decoupling layer. By sending messages to a third party - the message broker - a message-producing application no longer has to know about all the applications that are interested in its information. The message broker can provide queues that carry the messages to interested message consuming applications. The message broker also provides a buffer that allows the applications involved to produce and consume data at different rates.

Red Hat Enterprise Messaging provides a messaging broker based on the Apache Qpid project. It implements AMQP (Advanced Messaging Queue Protocol) messaging.