Prometheus Instrumentation Sample

httpserver.go

package main

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

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

var (
	errorCount = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "greeting_error_count_total",
		Help: "Counter of HTTP requests resulting in an error.",
	})
)

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

func main() {
	helloHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		rand.Seed(time.Now().UnixNano())
		switch rand.Intn(4) {
		case 0:
			log.Println("Hello!")
			fmt.Fprint(w, "Hello!")
		case 1:
			log.Println("Hi!")
			fmt.Fprint(w, "Hi!")
		case 2:
			log.Println("Hey!")
			fmt.Fprint(w, "Hey!")
		case 3:
			log.Println("Error!")
			errorCount.Inc()
			fmt.Fprint(w, "Error!!")
		}
	})
	http.Handle("/", helloHandler)
	http.Handle("/metrics", promhttp.Handler())
	log.Fatal(http.ListenAndServe(":8080", nil))
}

Sweet!