code: func (l *LoadBalancer) trackConnection(backend NetAddr, conn net.Conn) int64 {
  	l.Lock()
  	defer l.Unlock()
  	l.connID += 1
  	tracker, ok := l.connections[backend]
  	if !ok {
  		tracker = make(map[int64]net.Conn)
  		l.connections[backend] = tracker
  	}
  	tracker[l.connID] = conn
  	return l.connID
  }
docs: // trackeConnection adds connection to the connection tracker