code: func NewConnectionsLimiter(config LimiterConfig) (*ConnectionsLimiter, error) {
  	limiter := ConnectionsLimiter{
  		Mutex:          &sync.Mutex{},
  		maxConnections: config.MaxConnections,
  		connections:    make(map[string]int64),
  	}
  
  	ipExtractor, err := utils.NewExtractor("client.ip")
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	limiter.ConnLimiter, err = connlimit.New(
  		nil, ipExtractor, config.MaxConnections)
  	if err != nil {
  		return nil, trace.Wrap(err)
  	}
  
  	return &limiter, nil
  }
docs: // NewConnectionsLimiter returns new connection limiter, in case if connection
  // limits are not set, they won't be tracked