private void fetchAndSetActiveMasterServerName() {
    LOG.debug("Attempting to fetch active master sn from zk");
    try {
      activeMasterServerName = MasterAddressTracker.getMasterAddress(watcher);
    } catch (IOException | KeeperException e) {
      // Log and ignore for now and re-fetch later if needed.
      LOG.error("Error fetching active master information", e);
    }
  }
Fetches the active master's ServerName from zookeeper.
hbase-server/src/main/java/org/apache/hadoop/hbase/master/ActiveMasterManager.java