Graceful Server Shutdown in Go

main.go

package main

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

func countdown(w http.ResponseWriter, r *http.Request) {
	var flush func()
	if f, ok := w.(http.Flusher); ok {
		flush = func() {
			f.Flush()
		}
	}

	io.WriteString(w, "Countdown initiated...\n")
	for i := 10; i > 0; i-- {
		flush()
		time.Sleep(1 * time.Second)
		fmt.Fprintf(w, "%d\n", i)
	}
	io.WriteString(w, "BOOM!\n")
}

func main() {
	stop := make(chan os.Signal, 1)
	signal.Notify(stop, os.Interrupt)

	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
	}
	addr := "127.0.0.1:" + port

	mux := http.NewServeMux()
	mux.HandleFunc("/", countdown)

	server := http.Server{
		Addr:         addr,
		Handler:      mux,
		ReadTimeout:  60 * time.Second,
		WriteTimeout: 60 * time.Second,
	}

	go func() {
		log.Printf("Started listening on: http://%s/", server.Addr)
		err := server.ListenAndServe()
		if err != http.ErrServerClosed {
			log.Fatal(err)
		}
	}()

	<-stop

	timeout := 30 * time.Second
	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()

	log.Printf("Shutting down...")
	server.Shutdown(ctx)
}