When joining or leaving a cluster, there's an obvious state change: data that lives on other cluster nodes either becomes available, or access to that data is lost. In certain instances, it might be needed to trigger event listeners, or follow up with additional actions.

In particular, evaluate if it is needed that other cluster nodes (re)generate presence updates to make the joining node aware of sessions that exist on them. This could be similar to what already is implemented for the joining node: it iterates over all its local client routes and simulates that they just became available (see org.jivesoftware.openfire.spi.RoutingTableImpl#joinedCluster()