private void reportNewRegionServers(final ClusterMetrics clusterMetrics) {
    final Set<Address> regionServers = collectKnownRegionServers(clusterMetrics);
    final Set<Address> newRegionServers = new HashSet<>(regionServers);
    newRegionServers.removeAll(initialRegionServers);
    if (!newRegionServers.isEmpty()) {
      final StringBuilder stringBuilder =
        new StringBuilder().append("region server(s) are new for this cluster report");
      newRegionServers.stream().sorted()
        .forEach(address -> stringBuilder.append("\n  ").append(address));
      getLogger().warn(stringBuilder.toString());
    }
  }
Build a set of all the host:port pairs of region servers known to this cluster.
hbase-it/src/test/java/org/apache/hadoop/hbase/chaos/actions/DumpClusterStatusAction.java