@Override
  public List<ConsensusGroupId> getAllConsensusGroupIds() {
    List<ConsensusGroupId> ids = new ArrayList<>();
    try {
      server
          .get()
          .getGroupIds()
          .forEach(groupId -> ids.add(Utils.fromRaftGroupIdToConsensusGroupId(groupId)));
      return ids;
    } catch (IOException e) {
      return Collections.emptyList();
    }
  }
returns the known leader to the given group. NOTICE: if the local peer isn't a member of given
group, getLeader will return null.

@return null if local peer isn't in group, otherwise group leader.
iotdb-core/consensus/src/main/java/org/apache/iotdb/consensus/ratis/RatisConsensus.java