Cluster Size

For delivery assurance with fault tolerance, use a minimum cluster size of 3 servers, so that a quorum can exist even when one server is unavailable.

A cluster of 2 servers is invalid, because when one server is unavailable, the remaining server cannot form a quorum on its own. It is an error to configure only 2 servers.

For apportioning message streams, a cluster of only 1 server is a valid configuration.