Prometheus example in Go

prometheus.go

package main

import (
	"fmt"
	"log"
	"math/rand"
	"net/http"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/prometheus/client_golang/prometheus/promauto"
	"github.com/prometheus/client_golang/prometheus/promhttp"
)

var (
	requestDuration = prometheus.NewHistogram(prometheus.HistogramOpts{
		Name:    "request_duration_milliseconds",
		Help:    "Request duration distribution.",
		Buckets: prometheus.LinearBuckets(0, 40, 5),
	})

	requests = promauto.NewCounter(
		prometheus.CounterOpts{
			Name: "requests_total",
			Help: "The total number of requests",
		})
)

func init() {
	prometheus.MustRegister(requestDuration)
}

func main() {
	handler := func(w http.ResponseWriter, r *http.Request) {
		delay := rand.Intn(200)

		requests.Inc()                          // increment counter
		requestDuration.Observe(float64(delay)) // send metric

		time.Sleep(time.Duration(delay) * time.Millisecond)  // sleep for random
		fmt.Fprintf(w, "Response in %d milliseconds", delay) // response
	}

	http.HandleFunc("/", handler)
	http.Handle("/metrics", promhttp.Handler())
	log.Fatal(http.ListenAndServe(":8000", nil))

	return
}