public Map<ServerName, ServerMetrics> getOnlineServers() {
    // Presumption is that iterating the returned Map is OK.
    synchronized (this.onlineServers) {
      return Collections.unmodifiableMap(this.onlineServers);
    }
  }
Returns Read-only map of servers to serverinfo
hbase-server/src/main/java/org/apache/hadoop/hbase/master/ServerManager.java