func serve() {
	http.Handle("/metrics", promhttp.Handler())
	logrus.WithError(http.ListenAndServe(":8080", nil)).Fatal("ListenAndServe returned.")
}
func serve() {
	http.Handle("/metrics", promhttp.Handler())
	logrus.WithError(http.ListenAndServe(":8080", nil)).Fatal("ListenAndServe returned.")
}
// serve starts a http server and serves prometheus metrics.
// Meant to be called inside a goroutine.