@Override
  public void nodeChildrenChanged(String path) {
    if (path.equals(watcher.getZNodePaths().backupMasterAddressesZNode)) {
      try {
        updateBackupMasters();
      } catch (InterruptedIOException ioe) {
        LOG.error("Error updating backup masters", ioe);
      }
    }
  }
@param watcher ZK watcher
@param sn      ServerName
@param master  In an instance of a Master.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/ActiveMasterManager.java