Universal Messaging Deployment Guide - Server Failover / High Availability
In order to provide your clients with a service that is highly available, clustering is recommended. Clusters enable transparency across your clients. If one server becomes unavailable, the client will automatically reconnect to another realm within the cluster. All cluster objects within the realm are replicated among all cluster realms and their state is maintained exactly the same across all realm members. Therefore whenever a client disconnects from one realm and reconnects to another, they will resume from the same position on the newly connected realm.
When a client provides a list of RNAMES as a comma separated list, if each entry in the list corresponds to realm that is a member of the cluster, then the client will reconnect to the next realm in the cluster list.
For more information on clustering, please see the clustering section in the Administrators Guide.