public int getBackupMasterInfoPort(final ServerName sn) {
    try {
      return MasterAddressTracker.getBackupMasterInfoPort(watcher, sn);
    } catch (Exception e) {
      LOG.warn("Failed to get backup master: " + sn + "'s info port.", e);
      return 0;
    }
  }
Fetches the active master's ServerName from zookeeper.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/ActiveMasterManager.java