code: func NewGraylogHook(addr string, extra map[string]interface{}) *GraylogHook {
  	g, err := NewWriter(addr)
  	if err != nil {
  		logrus.WithError(err).Error("Can't create Gelf logger")
  	}
  
  	host, err := os.Hostname()
  	if err != nil {
  		host = "localhost"
  	}
  
  	hook := &GraylogHook{
  		Host:        host,
  		Extra:       extra,
  		Level:       logrus.DebugLevel,
  		gelfLogger:  g,
  		synchronous: true,
  	}
  	return hook
  }
docs: // NewGraylogHook creates a hook to be added to an instance of logger.