code: func TunnelConnectionStatus(clock clockwork.Clock, conn TunnelConnection) string {
  	diff := clock.Now().Sub(conn.GetLastHeartbeat())
  	if diff < defaults.ReverseTunnelOfflineThreshold {
  		return teleport.RemoteClusterStatusOnline
  	}
  	return teleport.RemoteClusterStatusOffline
  }
docs: // IsTunnelConnectionStatus returns tunnel connection status based on the last
  // heartbeat time recorded for a connection