code: private boolean isHub(ServerBartender server)
    {
      int upCount = 0;
      
      for (ServerHeartbeat rackServer : _rack.getServers()) {
        if (rackServer == null || ! rackServer.isUp()) {
          continue;
        }
        
        if (rackServer == server && upCount < _hubCount) {
          return true;
        }
        
        upCount++;
          
        if (_hubCount <= upCount) {
          return false;
        }
      }
      
      return false;
    }
docs: Test if the server is a hub server for its rack.
  
  The hub are the first few active servers, where the servers are sorted by
  IP address and port. The default hub count is 3.