public List<ReplicationPeerDescription> listPeers(Pattern pattern) {
    if (pattern == null) {
      return new ArrayList<>(peers.values());
    }
    return peers.values().stream().filter(r -> pattern.matcher(r.getPeerId()).matches())
      .collect(Collectors.toList());
  }
Returns the old desciption of the peer
hbase-server/src/main/java/org/apache/hadoop/hbase/master/replication/ReplicationPeerManager.java