public NodeID getNodeID() {
        return nodeID == null ? DEFAULT_NODE_ID : nodeID;
    }
Returns an ID that uniquely identifies this server in a cluster. When not running in cluster mode
the returned value is always the same. However, when in cluster mode the value should be set
when joining the cluster and must be unique even upon restarts of this node.

@return an ID that uniquely identifies this server in a cluster.
xmppserver/src/main/java/org/jivesoftware/openfire/XMPPServer.java