What is idiomatic way to signal fx app to stop when server errors

[anivanovic]

As titled my question is what is preferred way to notify fx app to stop if I get error from server.ListenAndServe() method? Currently my code registers bunch of Providers and one Invoke which starts up my http server. Example code is like this:

fx.Invoke(startServer)

func startServer(lc fx.Lifecycle, router *chi.Mux, cfg *config.Env, app *models.Application) error {
	server := &http.Server{
		Addr:         fmt.Sprintf(":%s", 8080),
		Handler:      router,
	}

	lc.Append(fx.Hook{
		OnStart: func(ctx context.Context) error {
			go func() {
				if err := server.ListenAndServe(); err != nil {
					log.Err(err).Msg("Application server error while running")
					// notify app to stop
					syscall.Kill(os.Getpid(), syscall.SIGINT)
				}
			}()

			log.Info().Msgf("Application ready on port %v", port)
			return nil
		},
		OnStop: func(ctx context.Context) error {
			log.Info().Msg("Application shutting down")
			return multierr.Combine(
				server.Shutdown(ctx),
				app.Close(),
			)
		},
	})

	return nil
}

If I get error from server.ListenAndServe() I use syscall.Kill() to notify fx to stop application and exit. I run app with fxApp.Run(). It there better way to do this?

[anivanovic]

@sywhang I am tagging you as I see you did most recent changes. Is there recommended way to do this in fx or this is currently the best way?

[abhinav]

Hi there! Typically, you can use the fx.Shutdowner type to signal that the app should be shut down. This interface is provided to your container by default so you can just add it as a parameter to your provied/invoked function.

However, for the case of net/http.Server, note that per the documentation that Sever.ListenAndServe always returns a non-nil error—even if you called Shutdown or Close. So you probably want to ignore ErrServerClosed:

if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed)  {
  shutdowner.Shutdown()
}

Hope this helps!

[anivanovic]

Thanks on your reply. I would suggest to add this to example in the docs also as I could not figure out this one on my own.