feat: support multiple metrics addresses via repeated flag

cmd/cloudflared/tunnel/cmd.go

@@ -445,13 +445,15 @@ func StartServer(
 		return err
 	}
 
-	metricsListener, err := metrics.CreateMetricsListener(&listeners, c.String("metrics"))
+	metricsListeners, err := metrics.CreateMetricsListener(&listeners, c.StringSlice("metrics"))
 	if err != nil {
 		log.Err(err).Msg("Error opening metrics server listener")
 		return errors.Wrap(err, "Error opening metrics server listener")
 	}
 
-	defer metricsListener.Close()
+	for _, l := range metricsListeners {
+		defer l.Close()
+	}
 	wg.Add(1)
 
 	go func() {
@@ -484,7 +486,7 @@ func StartServer(
 			QuickTunnelHostname: quickTunnelURL,
 			Orchestrator:        orchestrator,
 		}
-		errC <- metrics.ServeMetrics(metricsListener, ctx, metricsConfig, log)
+		errC <- metrics.ServeMetrics(metricsListeners, ctx, metricsConfig, log)
 	}()
 
 	reconnectCh := make(chan supervisor.ReconnectSignal, c.Int(cfdflags.HaConnections))
@@ -877,9 +879,9 @@ func configureCloudflaredFlags(shouldHide bool) []cli.Flag {
 			Value:   false,
 			Hidden:  shouldHide,
 		}),
-		altsrc.NewStringFlag(&cli.StringFlag{
+		altsrc.NewStringSliceFlag(&cli.StringSliceFlag{
 			Name:  cfdflags.Metrics,
-			Value: metrics.GetMetricsDefaultAddress(metrics.Runtime),
+			Value: cli.NewStringSlice(metrics.GetMetricsDefaultAddress(metrics.Runtime)),
 			Usage: fmt.Sprintf(
 				`Listen address for metrics reporting. If no address is passed cloudflared will try to bind to %v.
 If all are unavailable, a random port will be used. Note that when running cloudflared from an virtual

cmd/cloudflared/tunnel/subcommands.go

@@ -478,10 +478,11 @@ func buildReadyCommand() *cli.Command {
 }
 
 func readyCommand(c *cli.Context) error {
-	metricsOpts := c.String(flags.Metrics)
+	metricsAddrs := c.StringSlice(flags.Metrics)
-	if !c.IsSet(flags.Metrics) {
+	if len(metricsAddrs) == 0 {
 		return errors.New("--metrics has to be provided")
 	}
+	metricsOpts := metricsAddrs[0]
 
 	requestURL := fmt.Sprintf("http://%s/ready", metricsOpts)
 	req, err := http.NewRequest(http.MethodGet, requestURL, nil)

metrics/metrics.go

@@ -99,44 +99,53 @@ func newMetricsHandler(
 	return router
 }
 
-// CreateMetricsListener will create a new [net.Listener] by using an
+// CreateMetricsListener will create a new set of [net.Listener] by using an
 // known set of ports when the default address is passed with the fallback
 // of choosing a random port when none is available.
 //
 // In case the provided address is not the default one then it will be used
 // as is.
-func CreateMetricsListener(listeners *gracenet.Net, laddr string) (net.Listener, error) {
+func CreateMetricsListener(listeners *gracenet.Net, laddrs []string) ([]net.Listener, error) {
-	if laddr == GetMetricsDefaultAddress(Runtime) {
+	// If the user didn't provide any address, use the default one
+	if len(laddrs) == 1 && laddrs[0] == GetMetricsDefaultAddress(Runtime) {
 		// On the presence of the default address select
 		// a port from the known set of addresses iteratively.
 		addresses := GetMetricsKnownAddresses(Runtime)
 		for _, address := range addresses {
 			listener, err := listeners.Listen("tcp", address)
 			if err == nil {
-				return listener, nil
+				return []net.Listener{listener}, nil
 			}
 		}
 
 		// When no port is available then bind to a random one
-		listener, err := listeners.Listen("tcp", laddr)
+		listener, err := listeners.Listen("tcp", laddrs[0])
 		if err != nil {
 			return nil, fmt.Errorf("failed to listen to default metrics address: %w", err)
 		}
 
-		return listener, nil
+		return []net.Listener{listener}, nil
 	}
 
-	// Explicitly got a local address then bind to it
+	// Explicitly got local addresses then bind to them
+	var ls []net.Listener
+	for _, laddr := range laddrs {
 		listener, err := listeners.Listen("tcp", laddr)
 		if err != nil {
+			// Close already opened listeners
+			for _, l := range ls {
+				l.Close()
+			}
 			return nil, fmt.Errorf("failed to bind to address (%s): %w", laddr, err)
 		}
+		ls = append(ls, listener)
+	}
 
-	return listener, nil
+	return ls, nil
 }
 
 func ServeMetrics(
-	l net.Listener,
+	listeners []net.Listener,
 	ctx context.Context,
 	config Config,
 	log *zerolog.Logger,
@@ -153,12 +162,17 @@ func ServeMetrics(
 		Handler:      h,
 	}
 
+	for _, l := range listeners {
 		wg.Add(1)
-	go func() {
+		go func(l net.Listener) {
 			defer wg.Done()
-		err = server.Serve(l)
+			if serveErr := server.Serve(l); serveErr != nil && serveErr != http.ErrServerClosed {
-	}()
+				log.Err(serveErr).Msgf("Metrics server failed on %s", l.Addr())
+			}
+		}(l)
 		log.Info().Msgf("Starting metrics server on %s", fmt.Sprintf("%v/metrics", l.Addr()))
+	}
+
 	// server.Serve will hang if server.Shutdown is called before the server is
 	// fully started up. So add artificial delay.
 	time.Sleep(startupTime)
@@ -174,13 +188,9 @@ func ServeMetrics(
 	cancel()
 
 	wg.Wait()
-	if err == http.ErrServerClosed {
 	log.Info().Msg("Metrics server stopped")
 	return nil
 }
-	log.Err(err).Msg("Metrics server failed")
-	return err
-}
 
 func RegisterBuildInfo(buildType, buildTime, version string) {
 	buildInfo := prometheus.NewGaugeVec(

metrics/metrics_test.go

@@ -13,28 +13,49 @@ import (
 func TestMetricsListenerCreation(t *testing.T) {
 	t.Parallel()
 	listeners := gracenet.Net{}
-	listener1, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	ls1, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
+	require.NoError(t, err)
+	require.Len(t, ls1, 1)
+	listener1 := ls1[0]
 	assert.Equal(t, "127.0.0.1:20241", listener1.Addr().String())
+
+	ls2, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
 	require.NoError(t, err)
-	listener2, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	require.Len(t, ls2, 1)
+	listener2 := ls2[0]
 	assert.Equal(t, "127.0.0.1:20242", listener2.Addr().String())
+
+	ls3, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
 	require.NoError(t, err)
-	listener3, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	require.Len(t, ls3, 1)
+	listener3 := ls3[0]
 	assert.Equal(t, "127.0.0.1:20243", listener3.Addr().String())
+
+	ls4, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
 	require.NoError(t, err)
-	listener4, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	require.Len(t, ls4, 1)
+	listener4 := ls4[0]
 	assert.Equal(t, "127.0.0.1:20244", listener4.Addr().String())
+
+	ls5, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
 	require.NoError(t, err)
-	listener5, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	require.Len(t, ls5, 1)
+	listener5 := ls5[0]
 	assert.Equal(t, "127.0.0.1:20245", listener5.Addr().String())
+
+	ls6, err := metrics.CreateMetricsListener(&listeners, []string{metrics.GetMetricsDefaultAddress("host")})
 	require.NoError(t, err)
-	listener6, err := metrics.CreateMetricsListener(&listeners, metrics.GetMetricsDefaultAddress("host"))
+	require.Len(t, ls6, 1)
+	listener6 := ls6[0]
 	addresses := [5]string{"127.0.0.1:20241", "127.0.0.1:20242", "127.0.0.1:20243", "127.0.0.1:20244", "127.0.0.1:20245"}
 	assert.NotContains(t, addresses, listener6.Addr().String())
+
+	ls7, err := metrics.CreateMetricsListener(&listeners, []string{"localhost:12345"})
 	require.NoError(t, err)
-	listener7, err := metrics.CreateMetricsListener(&listeners, "localhost:12345")
+	require.Len(t, ls7, 1)
+	listener7 := ls7[0]
 	assert.Equal(t, "127.0.0.1:12345", listener7.Addr().String())
-	require.NoError(t, err)
+
 	err = listener1.Close()
 	require.NoError(t, err)
 	err = listener2.Close()
@@ -49,4 +70,14 @@ func TestMetricsListenerCreation(t *testing.T) {
 	require.NoError(t, err)
 	err = listener7.Close()
 	require.NoError(t, err)
+
+	ls8, err := metrics.CreateMetricsListener(&listeners, []string{"127.0.0.1:12346", "127.0.0.1:12347"})
+	require.NoError(t, err)
+	require.Len(t, ls8, 2)
+	assert.Equal(t, "127.0.0.1:12346", ls8[0].Addr().String())
+	assert.Equal(t, "127.0.0.1:12347", ls8[1].Addr().String())
+	err = ls8[0].Close()
+	require.NoError(t, err)
+	err = ls8[1].Close()
+	require.NoError(t, err)
 }