In addition to providing for message service scalability, broker clusters also provide for message service availability. If one broker in a cluster fails, then other brokers in the cluster are available to continue to provide messaging services to client applications.
Message Queue supports two clustering models that provide different degrees of availability:
Conventional broker clusters. A conventional broker cluster provides message service availability. When a broker or a connection fails, clients connected to the failed broker reconnect to another broker in the cluster. However, messages and state information stored in the failed broker cannot be recovered until the failed broker is brought back online. This can result in an interruption of message delivery.
Enhanced broker clusters. An enhanced broker cluster provides data availability in addition to message service availability. When a broker or a connection fails, another broker takes over the pending work of the failed broker. The failover broker has access to the failed broker's messages and state information. Clients connected to the failed broker reconnect to the failover broker. In an enhanced cluster, as compared to a conventional cluster, a failure results in no interruption of message delivery.
You can also achieve data availability in a conventional cluster by using Solaris Cluster software. Solaris Cluster software replicates broker data and provides for a hot standby broker to take over the pending work of a failed broker. For details, see the documentation for the Solaris Cluster Data Service Agent for Message Queue.