@Override
    public void joinedCluster(final byte[] nodeIdBytes) {
        final String nodeName = getNodeName(nodeIdBytes);
        final NodeID nodeId = NodeID.getInstance(nodeIdBytes);
        nodeNames.put(nodeId, nodeName);
        LOGGER.info("Another node ({}/{}) has joined the cluster [seniorMember={}]", nodeId, nodeName, getSeniorMember());
        if (ClusterManager.isSeniorClusterMember() && nodeHasLeftCluster) {
            sendMessageToAdminsIfEnabled(nodeName + " has joined the cluster - resilience is restored");
        }
    }
Monitors the state of the cluster, and warns admins when nodes leave or rejoin the cluster
xmppserver/src/main/java/org/jivesoftware/openfire/cluster/ClusterMonitor.java