Add support for UDP routing in systemd socket activation

docs/content/routing/entrypoints.md

@@ -1240,7 +1240,7 @@ entryPoints:
 
 Traefik supports [systemd socket activation](https://www.freedesktop.org/software/systemd/man/latest/systemd-socket-activate.html).
 
-When a socket activation file descriptor name matches an EntryPoint name, the corresponding file descriptor will be used as the TCP listener for the matching EntryPoint.
+When a socket activation file descriptor name matches an EntryPoint name, the corresponding file descriptor will be used as the TCP/UDP listener for the matching EntryPoint.
 
 ```bash
 systemd-socket-activate -l 80 -l 443 --fdname web:websecure  ./traefik --entrypoints.web --entrypoints.websecure
@@ -1248,16 +1248,16 @@ systemd-socket-activate -l 80 -l 443 --fdname web:websecure  ./traefik --entrypo
 
 !!! warning "EntryPoint Address"
 
-    When a socket activation file descriptor name matches an EntryPoint name its address configuration is ignored.     
-
-!!! warning "TCP Only"
-
-    Socket activation is not yet supported with UDP entryPoints.
+    When a socket activation file descriptor name matches an EntryPoint name its address configuration is ignored. For support UDP routing, address must have /udp suffix (--entrypoints.my-udp-entrypoint.address=/udp)
 
 !!! warning "Docker Support"
 
     Socket activation is not supported by Docker but works with Podman containers.
 
+!!! warning "Multiple listeners in socket file"
+
+    Each systemd socket file must contain only one Listen directive, except in the case of HTTP/3, where the file must include both ListenStream and ListenDatagram directives. To set up TCP and UDP listeners on the same port, use multiple socket files with different entrypoints names.
+
 ## Observability Options
 
 This section is dedicated to options to control observability for an EntryPoint.

pkg/server/server_entrypoint_tcp.go

@@ -48,15 +48,8 @@ const (
 var (
 	clientConnectionStates   = map[string]*connState{}
 	clientConnectionStatesMu = sync.RWMutex{}
-
-	socketActivationListeners map[string]net.Listener
 )
 
-func init() {
-	// Populates pre-defined socketActivationListeners by socket activation.
-	populateSocketActivationListeners()
-}
-
 type connState struct {
 	State            string
 	KeepAliveState   string
@@ -204,7 +197,7 @@ func NewTCPEntryPoint(ctx context.Context, name string, config *static.EntryPoin
 		return nil, fmt.Errorf("error preparing https server: %w", err)
 	}
 
-	h3Server, err := newHTTP3Server(ctx, config, httpsServer)
+	h3Server, err := newHTTP3Server(ctx, name, config, httpsServer)
 	if err != nil {
 		return nil, fmt.Errorf("error preparing http3 server: %w", err)
 	}
@@ -476,13 +469,14 @@ func buildListener(ctx context.Context, name string, config *static.EntryPoint)
 	var err error
 
 	// if we have predefined listener from socket activation
-	if ln, ok := socketActivationListeners[name]; ok {
-		listener = ln
-	} else {
-		if len(socketActivationListeners) > 0 {
-			log.Warn().Str("name", name).Msg("Unable to find socket activation listener for entryPoint")
+	if socketActivation.isEnabled() {
+		listener, err = socketActivation.getListener(name)
+		if err != nil {
+			log.Ctx(ctx).Warn().Err(err).Str("name", name).Msg("Unable to use socket activation for entrypoint")
 		}
+	}
 
+	if listener == nil {
 		listenConfig := newListenConfig(config)
 		listener, err = listenConfig.Listen(ctx, "tcp", config.GetAddress())
 		if err != nil {

pkg/server/server_entrypoint_tcp_http3.go

@@ -25,19 +25,32 @@ type http3server struct {
 	getter func(info *tls.ClientHelloInfo) (*tls.Config, error)
 }
 
-func newHTTP3Server(ctx context.Context, configuration *static.EntryPoint, httpsServer *httpServer) (*http3server, error) {
-	if configuration.HTTP3 == nil {
+func newHTTP3Server(ctx context.Context, name string, config *static.EntryPoint, httpsServer *httpServer) (*http3server, error) {
+	var conn net.PacketConn
+	var err error
+
+	if config.HTTP3 == nil {
 		return nil, nil
 	}
 
-	if configuration.HTTP3.AdvertisedPort < 0 {
+	if config.HTTP3.AdvertisedPort < 0 {
 		return nil, errors.New("advertised port must be greater than or equal to zero")
 	}
 
-	listenConfig := newListenConfig(configuration)
-	conn, err := listenConfig.ListenPacket(ctx, "udp", configuration.GetAddress())
-	if err != nil {
-		return nil, fmt.Errorf("starting listener: %w", err)
+	// if we have predefined connections from socket activation
+	if socketActivation.isEnabled() {
+		conn, err = socketActivation.getConn(name)
+		if err != nil {
+			log.Ctx(ctx).Warn().Err(err).Str("name", name).Msg("Unable to use socket activation for entrypoint")
+		}
+	}
+
+	if conn == nil {
+		listenConfig := newListenConfig(config)
+		conn, err = listenConfig.ListenPacket(ctx, "udp", config.GetAddress())
+		if err != nil {
+			return nil, fmt.Errorf("starting listener: %w", err)
+		}
 	}
 
 	h3 := &http3server{
@@ -48,8 +61,8 @@ func newHTTP3Server(ctx context.Context, configuration *static.EntryPoint, https
 	}
 
 	h3.Server = &http3.Server{
-		Addr:      configuration.GetAddress(),
-		Port:      configuration.HTTP3.AdvertisedPort,
+		Addr:      config.GetAddress(),
+		Port:      config.HTTP3.AdvertisedPort,
 		Handler:   httpsServer.Server.(*http.Server).Handler,
 		TLSConfig: &tls.Config{GetConfigForClient: h3.getGetConfigForClient},
 		QUICConfig: &quic.Config{

pkg/server/server_entrypoint_udp.go

@@ -16,9 +16,9 @@ import (
 type UDPEntryPoints map[string]*UDPEntryPoint
 
 // NewUDPEntryPoints returns all the UDP entry points, keyed by name.
-func NewUDPEntryPoints(cfg static.EntryPoints) (UDPEntryPoints, error) {
+func NewUDPEntryPoints(config static.EntryPoints) (UDPEntryPoints, error) {
 	entryPoints := make(UDPEntryPoints)
-	for entryPointName, entryPoint := range cfg {
+	for entryPointName, entryPoint := range config {
 		protocol, err := entryPoint.GetProtocol()
 		if err != nil {
 			return nil, fmt.Errorf("error while building entryPoint %s: %w", entryPointName, err)
@@ -28,7 +28,7 @@ func NewUDPEntryPoints(cfg static.EntryPoints) (UDPEntryPoints, error) {
 			continue
 		}
 
-		ep, err := NewUDPEntryPoint(entryPoint)
+		ep, err := NewUDPEntryPoint(entryPoint, entryPointName)
 		if err != nil {
 			return nil, fmt.Errorf("error while building entryPoint %s: %w", entryPointName, err)
 		}
@@ -85,14 +85,33 @@ type UDPEntryPoint struct {
 }
 
 // NewUDPEntryPoint returns a UDP entry point.
-func NewUDPEntryPoint(cfg *static.EntryPoint) (*UDPEntryPoint, error) {
-	listenConfig := newListenConfig(cfg)
-	listener, err := udp.Listen(listenConfig, "udp", cfg.GetAddress(), time.Duration(cfg.UDP.Timeout))
-	if err != nil {
-		return nil, err
+func NewUDPEntryPoint(config *static.EntryPoint, name string) (*UDPEntryPoint, error) {
+	var listener *udp.Listener
+	var err error
+
+	timeout := time.Duration(config.UDP.Timeout)
+
+	// if we have predefined connections from socket activation
+	if socketActivation.isEnabled() {
+		if conn, err := socketActivation.getConn(name); err == nil {
+			listener, err = udp.ListenPacketConn(conn, timeout)
+			if err != nil {
+				log.Warn().Err(err).Str("name", name).Msg("Unable to create socket activation listener")
+			}
+		} else {
+			log.Warn().Err(err).Str("name", name).Msg("Unable to use socket activation for entrypoint")
+		}
 	}
 
-	return &UDPEntryPoint{listener: listener, switcher: &udp.HandlerSwitcher{}, transportConfiguration: cfg.Transport}, nil
+	if listener == nil {
+		listenConfig := newListenConfig(config)
+		listener, err = udp.Listen(listenConfig, "udp", config.GetAddress(), timeout)
+		if err != nil {
+			return nil, fmt.Errorf("error creating listener: %w", err)
+		}
+	}
+
+	return &UDPEntryPoint{listener: listener, switcher: &udp.HandlerSwitcher{}, transportConfiguration: config.Transport}, nil
 }
 
 // Start commences the listening for ep.

pkg/server/server_entrypoint_udp_test.go

@@ -24,7 +24,7 @@ func TestShutdownUDPConn(t *testing.T) {
 	}
 	ep.SetDefaults()
 
-	entryPoint, err := NewUDPEntryPoint(&ep)
+	entryPoint, err := NewUDPEntryPoint(&ep, "")
 	require.NoError(t, err)
 
 	go entryPoint.Start(context.Background())

pkg/server/socket_activation.go

@@ -0,0 +1,41 @@
+package server
+
+import (
+	"errors"
+	"net"
+)
+
+type SocketActivation struct {
+	enabled   bool
+	listeners map[string]net.Listener
+	conns     map[string]net.PacketConn
+}
+
+func (s *SocketActivation) isEnabled() bool {
+	return s.enabled
+}
+
+func (s *SocketActivation) getListener(name string) (net.Listener, error) {
+	listener, ok := s.listeners[name]
+	if !ok {
+		return nil, errors.New("unable to find socket activation TCP listener for entryPoint")
+	}
+
+	return listener, nil
+}
+
+func (s *SocketActivation) getConn(name string) (net.PacketConn, error) {
+	conn, ok := s.conns[name]
+	if !ok {
+		return nil, errors.New("unable to find socket activation UDP listener for entryPoint")
+	}
+
+	return conn, nil
+}
+
+var socketActivation *SocketActivation
+
+func init() {
+	// Populates pre-defined TCP and UDP listeners provided by systemd socket activation.
+	socketActivation = populateSocketActivationListeners()
+}

pkg/server/socket_activation_unix.go

@@ -9,16 +9,36 @@ import (
 	"github.com/rs/zerolog/log"
 )
 
-func populateSocketActivationListeners() {
-	listenersWithName, _ := activation.ListenersWithNames()
+func populateSocketActivationListeners() *SocketActivation {
+	// We use Files api due to activation not providing method for get PacketConn with names
+	files := activation.Files(true)
+	sa := &SocketActivation{enabled: false}
+	sa.listeners = make(map[string]net.Listener)
+	sa.conns = make(map[string]net.PacketConn)
 
-	socketActivationListeners = make(map[string]net.Listener)
-	for name, lns := range listenersWithName {
-		if len(lns) != 1 {
-			log.Error().Str("listenersName", name).Msg("Socket activation listeners must have one and only one listener per name")
-			continue
+	if len(files) > 0 {
+		sa.enabled = true
+
+		for _, f := range files {
+			if lc, err := net.FileListener(f); err == nil {
+				_, ok := sa.listeners[f.Name()]
+				if ok {
+					log.Error().Str("listenersName", f.Name()).Msg("Socket activation TCP listeners must have one and only one listener per name")
+				} else {
+					sa.listeners[f.Name()] = lc
+				}
+				f.Close()
+			} else if pc, err := net.FilePacketConn(f); err == nil {
+				_, ok := sa.conns[f.Name()]
+				if ok {
+					log.Error().Str("listenersName", f.Name()).Msg("Socket activation UDP listeners must have one and only one listener per name")
+				} else {
+					sa.conns[f.Name()] = pc
+				}
+				f.Close()
+			}
 		}
-
-		socketActivationListeners[name] = lns[0]
 	}
+
+	return sa
 }

pkg/server/socket_activation_windows.go

@@ -2,4 +2,6 @@
 
 package server
 
-func populateSocketActivationListeners() {}
+func populateSocketActivationListeners() *SocketActivation {
+	return &SocketActivation{enabled: false}
+}

pkg/udp/conn.go

@@ -34,16 +34,12 @@ type Listener struct {
 	timeout time.Duration
 }
 
-// Listen creates a new listener.
-func Listen(listenConfig net.ListenConfig, network, address string, timeout time.Duration) (*Listener, error) {
+// Creates a new listener from PacketConn.
+func ListenPacketConn(packetConn net.PacketConn, timeout time.Duration) (*Listener, error) {
 	if timeout <= 0 {
 		return nil, errors.New("timeout should be greater than zero")
 	}
 
-	packetConn, err := listenConfig.ListenPacket(context.Background(), network, address)
-	if err != nil {
-		return nil, fmt.Errorf("listen packet: %w", err)
-	}
 	pConn, ok := packetConn.(*net.UDPConn)
 	if !ok {
 		return nil, errors.New("packet conn is not an UDPConn")
@@ -62,6 +58,25 @@ func Listen(listenConfig net.ListenConfig, network, address string, timeout time
 	return l, nil
 }
 
+// Listen creates a new listener.
+func Listen(listenConfig net.ListenConfig, network, address string, timeout time.Duration) (*Listener, error) {
+	if timeout <= 0 {
+		return nil, errors.New("timeout should be greater than zero")
+	}
+
+	packetConn, err := listenConfig.ListenPacket(context.Background(), network, address)
+	if err != nil {
+		return nil, fmt.Errorf("listen packet: %w", err)
+	}
+
+	l, err := ListenPacketConn(packetConn, timeout)
+	if err != nil {
+		return nil, fmt.Errorf("listen packet conn: %w", err)
+	}
+
+	return l, nil
+}
+
 // Accept waits for and returns the next connection to the listener.
 func (l *Listener) Accept() (*Conn, error) {
 	c := <-l.acceptCh