code: private void onServerLinkClose(String hostName)
    {
      ServerHeartbeat server = _root.getServer(hostName);
    
      if (server == null) {
        return;
      }
      
      if (! isHub(server) && ! isHub(_serverSelf)) {
        return;
      }
      
      if (server.onHeartbeatStop()) {
        onServerStop(server);
  
        if (server.getRack() != null) {
          server.getRack().update();
        }
        
        updateHeartbeats();
      }
    }
docs: The peer server is now down.