Profiling Go HTTP service with pprof and expvar

main.go

package main

import (
	"context"
	"expvar" // Register the expvar handlers
	"fmt"
	"log"
	"net/http"
	_ "net/http/pprof" // Register the pprof handlers
	"os"
	"runtime"
	"time"

	"github.com/vardius/shutdown"
)

// m contains the global program counters for the application.
var m = struct {
	gr  *expvar.Int
	req *expvar.Int
}{
	gr:  expvar.NewInt("goroutines"),
	req: expvar.NewInt("requests"),
}

// Metrics updates program counters.
func Metrics(next http.Handler) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		next.ServeHTTP(w, r)

		// Increment the request counter.
		m.req.Add(1)

		// Update the count for the number of active goroutines every 100 requests.
		if m.req.Value()%100 == 0 {
			m.gr.Set(int64(runtime.NumGoroutine()))
		}
	}

	return http.HandlerFunc(fn)
}

type DebugServer struct {
	*http.Server
}

// NewDebugServer provides new debug http server
func NewDebugServer(address string) *DebugServer {
	return &DebugServer{
		&http.Server{
			Addr:    address,
			Handler: http.DefaultServeMux,
		},
	}
}

var isDebug = os.Getenv("DEBUG") != ""

func main() {
	mux := http.NewServeMux()
	mux.HandleFunc("/", func(w http.ResponseWriter, req *http.Request) {
		fmt.Fprintf(w, "Welcome to the home page!")
	})

	httpServer := &http.Server{
		Addr:    ":8080",
		Handler: Metrics(mux), // wrap our server with metrics middleware
	}

	go func() {
		log.Printf("Server HTTP listen on %s:%d", "localhost", 8080)
		if err := httpServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			log.Fatal(fmt.Sprintf("ListenAndServe: %s", err))
		}
	}()

	var debugServer *DebugServer
	if isDebug {
		debugServer = NewDebugServer(fmt.Sprintf("%s:%d", "localhost", 6060))

		go func() {
			log.Printf("Server HTTP listen on %s:%d", "localhost", 6060)
			if err := debugServer.ListenAndServe(); err != nil && err != http.ErrServerClosed {
				log.Fatal(fmt.Sprintf("ListenAndServe: %s", err))
			}
		}()
	}

	stop := func() {
		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()

		if err := httpServer.Shutdown(ctx); err != nil {
			log.Fatalf("Server shutdown failed %s", err)
		}

		if debugServer != nil {
			if err := debugServer.Shutdown(ctx); err != nil {
				log.Fatalf("Debug server shutdown failed %s", err)
			}
		}
	}

	shutdown.GracefulStop(stop) // will block until shutdown signal is received
}