A cluster is a group of Brokers that functions as one logical Broker. All Brokers in a cluster maintain the same set of document types and client groups; however, they each support their own set of clients.

Clients can connect to a cluster and publish documents to or receive documents from a cluster. The cluster to which a client publishes documents takes care of forwarding those documents to subscribers that are connected to the cluster. To an individual publisher or subscriber, a cluster appears as one large Broker.

Brokers that operate in a cluster are peers. There is no "central" or "controlling" Broker. Each Broker in the cluster is responsible for notifying its peers of changes (for example, additions, deletions, or modifications) that occur to its document types or client groups. By dynamically propagating changes to all Brokers in this manner, document types and client groups remain synchronized across the entire cluster. Whenever a Broker joins or leaves a cluster, the peers are informed. When clients are deleted from a Broker in a cluster, other Brokers are not notified.