Golang Prometheus integration

main.go

package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"os/signal"
	"syscall"
	"time"

	"github.com/gorilla/mux"

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

func recordMetrics() {
	go func() {
		opsProcessed.Inc()
	}()
}

var (
	opsProcessed = promauto.NewCounter(prometheus.CounterOpts{
		Name: "go_hello_world_processed_ops_total",
		Help: "The total number of processed events",
	})
)

func handler(w http.ResponseWriter, r *http.Request) {
	query := r.URL.Query()
	name := query.Get("name")
	if name == "" {
		name = "Guest"
	}

	log.Printf("Received request for %s\n", name)
	w.Write([]byte(fmt.Sprintf("Hello, %s\n", name)))
	recordMetrics()
}

func healthHandler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
}

func readinessHandler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(http.StatusOK)
}

func main() {
	r := mux.NewRouter()

	r.HandleFunc("/", handler)
	r.HandleFunc("/health", healthHandler)
	r.HandleFunc("/readiness", readinessHandler)
	r.Handle("/metrics", promhttp.Handler())

	srv := &http.Server{
		Handler:      r,
		Addr:         ":8080",
		ReadTimeout:  10 * time.Second,
		WriteTimeout: 10 * time.Second,
	}

	go func() {
		log.Println("Starting Server")
		if err := srv.ListenAndServe(); err != nil {
			log.Fatal(err)
		}
	}()

	waitForShutdown(srv)
}

func waitForShutdown(srv *http.Server) {
	interruptChan := make(chan os.Signal, 1)
	signal.Notify(interruptChan, os.Interrupt, syscall.SIGINT, syscall.SIGTERM)

	<-interruptChan

	ctx, cancel := context.WithTimeout(context.Background(), time.Second*10)
	defer cancel()
	srv.Shutdown(ctx)

	log.Println("Shutting down")
	os.Exit(0)
}