Function InstrumentMetricHandler

prometheus/promhttp/http.go:286–321

InstrumentMetricHandler is usually used with an http.Handler returned by the HandlerFor function. It instruments the provided http.Handler with two metrics: A counter vector "promhttp_metric_handler_requests_total" to count scrapes partitioned by HTTP status code, and a gauge "promhttp_metric_handle

(reg prometheus.Registerer, handler http.Handler)

// "scrape_duration_seconds" gauge created by the Prometheus server upon each
// scrape.
func InstrumentMetricHandler(reg prometheus.Registerer, handler http.Handler) http.Handler {
	cnt := prometheus.NewCounterVec(
		prometheus.CounterOpts{
			Name: "promhttp_metric_handler_requests_total",
			Help: "Total number of scrapes by HTTP status code.",
		},
		[]string{"code"},
	)
	// Initialize the most likely HTTP status codes.
	cnt.WithLabelValues("200")
	cnt.WithLabelValues("500")
	cnt.WithLabelValues("503")
	if err := reg.Register(cnt); err != nil {
		are := &prometheus.AlreadyRegisteredError{}
		if errors.As(err, are) {
			cnt = are.ExistingCollector.(*prometheus.CounterVec)
		} else {
			panic(err)
		}
	}

	gge := prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "promhttp_metric_handler_requests_in_flight",
		Help: "Current number of scrapes being served.",
	})
	if err := reg.Register(gge); err != nil {
		are := &prometheus.AlreadyRegisteredError{}
		if errors.As(err, are) {
			gge = are.ExistingCollector.(prometheus.Gauge)
		} else {
			panic(err)
		}
	}

	return InstrumentHandlerCounter(cnt, InstrumentHandlerInFlight(gge, handler))
}

// HandlerErrorHandling defines how a Handler serving metrics will handle
// errors.