Improve signal handling

This commit starts to wire up better signal handling, it starts with
handling shutdown a bit better, using the graceful shutdown for all the
listeners we use.

It also adds the initial switch case for handling config and acl reload,
which is to be implemented.

app.go

@@ -567,19 +567,6 @@ func (h *Headscale) Serve() error {
 		return fmt.Errorf("failed change permission of gRPC socket: %w", err)
 	}
 
-	// Handle common process-killing signals so we can gracefully shut down:
-	sigc := make(chan os.Signal, 1)
-	signal.Notify(sigc, os.Interrupt, syscall.SIGTERM)
-	go func(c chan os.Signal) {
-		// Wait for a SIGINT or SIGKILL:
-		sig := <-c
-		log.Printf("Caught signal %s: shutting down.", sig)
-		// Stop listening (and unlink the socket if unix type):
-		socketListener.Close()
-		// And we're done:
-		os.Exit(0)
-	}(sigc)
-
 	grpcGatewayMux := runtime.NewServeMux()
 
 	// Make the grpc-gateway connect to grpc over socket
@@ -724,6 +711,48 @@ func (h *Headscale) Serve() error {
 	log.Info().
 		Msgf("listening and serving metrics on: %s", h.cfg.MetricsAddr)
 
+	// Handle common process-killing signals so we can gracefully shut down:
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc,
+		syscall.SIGHUP,
+		syscall.SIGINT,
+		syscall.SIGTERM,
+		syscall.SIGQUIT,
+		syscall.SIGHUP)
+	go func(c chan os.Signal) {
+		// Wait for a SIGINT or SIGKILL:
+		sig := <-c
+		switch sig {
+		case syscall.SIGHUP:
+			log.Info().
+				Str("signal", sig.String()).
+				Msg("Received SIGHUP, reloading ACL and Config")
+
+		// TODO(kradalby): Reload config on SIGHUP
+
+		default:
+			log.Info().
+				Str("signal", sig.String()).
+				Msg("Received signal to stop, shutting down gracefully")
+
+			// Gracefully shut down servers
+			promHTTPServer.Shutdown(ctx)
+			httpServer.Shutdown(ctx)
+			grpcSocket.GracefulStop()
+
+			// Close network listeners
+			promHTTPListener.Close()
+			httpListener.Close()
+			grpcGatewayConn.Close()
+
+			// Stop listening (and unlink the socket if unix type):
+			socketListener.Close()
+
+			// And we're done:
+			os.Exit(0)
+		}
+	}(sigc)
+
 	return errorGroup.Wait()
 }