@Override
  public RSGroupInfo getRSGroupOfServer(Address serverHostPort) throws IOException {
    SortedSet<Address> onlineServers = getOnlineServers();
    if (onlineServers.contains(serverHostPort)) {
      return new RSGroupInfo(RSGroupInfo.DEFAULT_GROUP, onlineServers);
    } else {
      return null;
    }
  }
A dummy RSGroupInfoManager which only contains a default rs group.
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/DisabledRSGroupInfoManager.java