gracefully shutdown go web server with error group

gracefully_shutdown_server.go

package main

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

//   "github.com/gorilla/mux"
	"github.com/gin-gonic/gin"
	"golang.org/x/sync/errgroup"
)

func main() {
	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

  // you can also use other HTTP router 
	router := gin.Default()
	router.GET("/", func(c *gin.Context) {
		time.Sleep(100 * time.Millisecond)
		c.String(http.StatusOK, "Welcome Gin Server")
	})
  
// 	router := mux.NewRouter()
// 	router.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
// 		time.Sleep(100 * time.Millisecond)
// 		w.WriteHeader(http.StatusOK)
// 		fmt.Fprintf(w, "Welcome Mux server")
// 	})

	srv := &http.Server{
		Addr:    ":8080",
		Handler: router,
	}

	errWg, errCtx := errgroup.WithContext(ctx)

	errWg.Go(func() error {
		if err := srv.ListenAndServe(); err != nil && err != http.ErrServerClosed {
			return err
		}
		return nil
	})

	errWg.Go(func() error {
		<-errCtx.Done()
		// https://gist.github.com/s8508235/bc248d046d5001d5cae46cc39066cdf5?permalink_comment_id=4360249#gistcomment-4360249
		return srv.Shutdown(context.Background()) 
	})

	err := errWg.Wait()

	if err == context.Canceled || err == nil {
		fmt.Println("gracefully quit server")
	} else if err != nil {
		fmt.Println(err)
	}
}

Are you sure you can pass errCtx to srv.Shutdown here https://gist.github.com/s8508235/bc248d046d5001d5cae46cc39066cdf5#file-gracefully_shutdown_server-go-L48-L52 ?

I think this should just be:

	errWg.Go(func() error {
		<-errCtx.Done()
		// no need to call stop, either the `ctx` is already cancelled or will be cancelled by the `defer` statement above
		return srv.Shutdown(context.Background()) // do not pass errCtx here, otherwise srv drops all connections instead of gracefully closing them, you can pass a new `context.WithTimeout` to limit how long the shutdown should take
	})

This way the err returned from errWg.Wait() should also be nil if the shutdown went well. If it is context.Canceled then srv.Shutdown couldn't gracefully shut down and dropped connections.

Thanks for your correction!!