private List<RSGroupInfo> retrieveGroupListFromGroupTable() throws IOException {
    List<RSGroupInfo> rsGroupInfoList = Lists.newArrayList();
    AsyncTable<?> table = conn.getTable(RSGROUP_TABLE_NAME);
    try (ResultScanner scanner = table.getScanner(META_FAMILY_BYTES, META_QUALIFIER_BYTES)) {
      for (Result result;;) {
        result = scanner.next();
        if (result == null) {
          break;
        }
        RSGroupProtos.RSGroupInfo proto = RSGroupProtos.RSGroupInfo
          .parseFrom(result.getValue(META_FAMILY_BYTES, META_QUALIFIER_BYTES));
        rsGroupInfoList.add(ProtobufUtil.toGroupInfo(proto));
      }
    }
    return rsGroupInfoList;
  }
Returns Set of online Servers named for their hostname and port (not ServerName).
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/RSGroupInfoManagerImpl.java