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.",
	})
	successCount = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "greeting_success_count_total",
		Help: "Counter of HTTP requests resulting in a success.",
	}, []string{"type"})
	requestCount = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "http_request_count_total",
		Help: "Counter of HTTP requests made.",
	}, []string{"code", "method"})
	requestDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "http_request_duration_seconds",
		Help:    "A histogram of latencies for requests.",
		Buckets: append([]float64{0.000001, 0.001, 0.003}, prometheus.DefBuckets...),
	}, []string{"code", "method"})
	responseSize = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "http_response_size_bytes",
		Help:    "A histogram of response sizes for requests.",
		Buckets: []float64{0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20},
	}, []string{"code", "method"})
)

func init() {
	prometheus.MustRegister(errorCount)
	prometheus.MustRegister(successCount)
	prometheus.MustRegister(requestCount)
	prometheus.MustRegister(requestDuration)
	prometheus.MustRegister(responseSize)
}

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!")
			successCount.WithLabelValues("hello").Inc()
			fmt.Fprint(w, "Hello!")
		case 1:
			log.Println("Hi!")
			successCount.WithLabelValues("hi").Inc()
			fmt.Fprint(w, "Hi!")
		case 2:
			log.Println("Hey!")
			successCount.WithLabelValues("hey").Inc()
			fmt.Fprint(w, "Hey!")
		case 3:
			log.Println("Error!")
			errorCount.Inc()
			fmt.Fprint(w, "Error!!")
		}
	})
	// Instrument helloHandler
	wrappedHelloHandler := promhttp.InstrumentHandlerCounter(requestCount,
		promhttp.InstrumentHandlerDuration(requestDuration,
			promhttp.InstrumentHandlerResponseSize(responseSize, helloHandler),
		),
	)
	http.Handle("/", wrappedHelloHandler)
	http.Handle("/metrics", promhttp.Handler())
	log.Fatal(http.ListenAndServe(":8080", nil))
}

Sweet!