code: func pushMetric(addr string, interval time.Duration) {
  	if interval == zeroDuration || len(addr) == 0 {
  		log.Info("disable Prometheus push client")
  		return
  	}
  	log.Info("start prometheus push client", zap.String("server addr", addr), zap.String("interval", interval.String()))
  	go prometheusPushClient(addr, interval)
  }
docs: // pushMetric pushes metrics in background.