private SortedSet<Address> getDefaultServers(List<RSGroupInfo> rsGroupInfoList) {
    // Build a list of servers in other groups than default group, from rsGroupMap
    Set<Address> serversInOtherGroup = new HashSet<>();
    for (RSGroupInfo group : rsGroupInfoList) {
      if (!RSGroupInfo.DEFAULT_GROUP.equals(group.getName())) { // not default group
        serversInOtherGroup.addAll(group.getServers());
      }
    }

    // Get all online servers from Zookeeper and find out servers in default group
    SortedSet<Address> defaultServers = Sets.newTreeSet();
    for (ServerName serverName : masterServices.getServerManager().getOnlineServers().keySet()) {
      Address server = Address.fromParts(serverName.getHostname(), serverName.getPort());
      if (!serversInOtherGroup.contains(server)) { // not in other groups
        defaultServers.add(server);
      }
    }
    return defaultServers;
  }
Update cache of rsgroups. Caller must be synchronized on 'this'.
@param currentGroups Current list of Groups.
hbase-server/src/main/java/org/apache/hadoop/hbase/rsgroup/RSGroupInfoManagerImpl.java