On client CloseWrite, do CloseWrite instead of Close for backend

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

docs/content/reference/dynamic-configuration/docker-labels.yml

@@ -184,4 +184,6 @@
 - "traefik.tcp.routers.tcprouter1.tls.options=foobar"
 - "traefik.tcp.routers.tcprouter1.tls.passthrough=true"
 - "traefik.tcp.services.tcpservice0.loadbalancer.server.port=foobar"
+- "traefik.tcp.services.tcpservice0.loadbalancer.terminationdelay=100"
 - "traefik.tcp.services.tcpservice1.loadbalancer.server.port=foobar"
+- "traefik.tcp.services.tcpservice1.loadbalancer.terminationdelay=100"

docs/content/reference/dynamic-configuration/file.toml

@@ -286,14 +286,17 @@
   [tcp.services]
     [tcp.services.TCPService0]
       [tcp.services.TCPService0.loadBalancer]
+        terminationDelay = 100
 
         [[tcp.services.TCPService0.loadBalancer.servers]]
           address = "foobar"
 
         [[tcp.services.TCPService0.loadBalancer.servers]]
           address = "foobar"
+
     [tcp.services.TCPService1]
       [tcp.services.TCPService1.loadBalancer]
+        terminationDelay = 100
 
         [[tcp.services.TCPService1.loadBalancer.servers]]
           address = "foobar"

docs/content/reference/dynamic-configuration/file.yaml

@@ -324,11 +324,13 @@ tcp:
   services:
     TCPService0:
       loadBalancer:
+        terminationDelay: 100
         servers:
         - address: foobar
         - address: foobar
     TCPService1:
       loadBalancer:
+        terminationDelay: 100
         servers:
         - address: foobar
         - address: foobar

docs/content/reference/dynamic-configuration/marathon-labels.json

@@ -184,4 +184,6 @@
 "traefik.tcp.routers.tcprouter1.tls.options": "foobar",
 "traefik.tcp.routers.tcprouter1.tls.passthrough": "true",
 "traefik.tcp.services.tcpservice0.loadbalancer.server.port": "foobar",
+"traefik.tcp.services.tcpservice0.loadbalancer.terminationDelay": "100",
 "traefik.tcp.services.tcpservice1.loadbalancer.server.port": "foobar"
+"traefik.tcp.services.tcpservice1.loadbalancer.terminationDelay": "100",

docs/content/routing/services/index.md

@@ -455,3 +455,34 @@ The `address` option (IP:Port) point to a specific instance.
             servers:
               address: "xx.xx.xx.xx:xx"
     ```
+
+#### Termination Delay
+
+As a proxy between a client and a server, it can happen that either side (e.g. client side) decides to terminate its writing capability on the connection (i.e. issuance of a FIN packet).
+The proxy needs to propagate that intent to the other side, and so when that happens, it also does the same on its connection with the other side (e.g. backend side).
+
+However, if for some reason (bad implementation, or malicious intent) the other side does not eventually do the same as well,
+the connection would stay half-open, which would lock resources for however long.
+
+To that end, as soon as the proxy enters this termination sequence, it sets a deadline on fully terminating the connections on both sides.
+
+The termination delay controls that deadline.
+It is a duration in milliseconds, defaulting to 100.
+A negative value means an infinite deadline (i.e. the connection is never fully terminated by the proxy itself).
+
+??? example "A Service with a termination delay -- Using the [File Provider](../../providers/file.md)"
+
+    ```toml tab="TOML"
+    [tcp.services]
+      [tcp.services.my-service.loadBalancer]
+        [[tcp.services.my-service.loadBalancer]]
+          terminationDelay = 200
+    ```
+
+    ```yaml tab="YAML"
+    tcp:
+      services:
+        my-service:
+          loadBalancer:
+            terminationDelay: 200
+    ```

integration/testdata/rawdata-crd.json

@@ -115,6 +115,7 @@
 	"tcpServices": {
 		"default/test3.route-673acf455cb2dab0b43a@kubernetescrd": {
 			"loadBalancer": {
+				"terminationDelay": 100,
 				"servers": [
 					{
 						"address": "10.42.0.4:8080"

pkg/config/dynamic/tcp_config.go

@@ -45,7 +45,19 @@ type RouterTCPTLSConfig struct {
 
 // TCPLoadBalancerService holds the LoadBalancerService configuration.
 type TCPLoadBalancerService struct {
-	Servers []TCPServer `json:"servers,omitempty" toml:"servers,omitempty" yaml:"servers,omitempty" label-slice-as-struct:"server"`
+	// TerminationDelay, corresponds to the deadline that the proxy sets, after one
+	// of its connected peers indicates it has closed the writing capability of its
+	// connection, to close the reading capability as well, hence fully terminating the
+	// connection. It is a duration in milliseconds, defaulting to 100. A negative value
+	// means an infinite deadline (i.e. the reading capability is never closed).
+	TerminationDelay *int        `json:"terminationDelay,omitempty" toml:"terminationDelay,omitempty" yaml:"terminationDelay,omitempty"`
+	Servers          []TCPServer `json:"servers,omitempty" toml:"servers,omitempty" yaml:"servers,omitempty" label-slice-as-struct:"server"`
+}
+
+// SetDefaults Default values for a TCPLoadBalancerService
+func (l *TCPLoadBalancerService) SetDefaults() {
+	defaultTerminationDelay := 100 // in milliseconds
+	l.TerminationDelay = &defaultTerminationDelay
 }
 
 // Mergeable tells if the given service is mergeable.

pkg/config/dynamic/zz_generated.deepcopy.go

@@ -1155,6 +1155,11 @@ func (in *TCPConfiguration) DeepCopy() *TCPConfiguration {
 // DeepCopyInto is an autogenerated deepcopy function, copying the receiver, writing into out. in must be non-nil.
 func (in *TCPLoadBalancerService) DeepCopyInto(out *TCPLoadBalancerService) {
 	*out = *in
+	if in.TerminationDelay != nil {
+		in, out := &in.TerminationDelay, &out.TerminationDelay
+		*out = new(int)
+		**out = **in
+	}
 	if in.Servers != nil {
 		in, out := &in.Servers, &out.Servers
 		*out = make([]TCPServer, len(*in))

pkg/config/label/label_test.go

@@ -170,7 +170,9 @@ func TestDecodeConfiguration(t *testing.T) {
 		"traefik.tcp.routers.Router1.tls.options":                                      "foo",
 		"traefik.tcp.routers.Router1.tls.passthrough":                                  "false",
 		"traefik.tcp.services.Service0.loadbalancer.server.Port":                       "42",
+		"traefik.tcp.services.Service0.loadbalancer.TerminationDelay":                  "42",
 		"traefik.tcp.services.Service1.loadbalancer.server.Port":                       "42",
+		"traefik.tcp.services.Service1.loadbalancer.TerminationDelay":                  "42",
 	}
 
 	configuration, err := DecodeConfiguration(labels)
@@ -212,6 +214,7 @@ func TestDecodeConfiguration(t *testing.T) {
 								Port: "42",
 							},
 						},
+						TerminationDelay: func(i int) *int { return &i }(42),
 					},
 				},
 				"Service1": {
@@ -221,6 +224,7 @@ func TestDecodeConfiguration(t *testing.T) {
 								Port: "42",
 							},
 						},
+						TerminationDelay: func(i int) *int { return &i }(42),
 					},
 				},
 			},

pkg/provider/docker/config.go

@@ -79,6 +79,7 @@ func (p *Provider) buildTCPServiceConfiguration(ctx context.Context, container d
 	if len(configuration.Services) == 0 {
 		configuration.Services = make(map[string]*dynamic.TCPService)
 		lb := &dynamic.TCPLoadBalancerService{}
+		lb.SetDefaults()
 		configuration.Services[serviceName] = &dynamic.TCPService{
 			LoadBalancer: lb,
 		}

pkg/provider/docker/config_test.go

@@ -13,6 +13,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func Int(v int) *int { return &v }
+
 func TestDefaultRule(t *testing.T) {
 	testCases := []struct {
 		desc        string
@@ -2092,6 +2094,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -2136,6 +2139,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -2190,6 +2194,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:8080",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -2268,6 +2273,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.2:8080",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -2331,6 +2337,53 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:8080",
 									},
 								},
+								TerminationDelay: Int(100),
+							},
+						},
+					},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+			},
+		},
+		{
+			desc: "tcp with label for tcp service, with termination delay",
+			containers: []dockerData{
+				{
+					ServiceName: "Test",
+					Name:        "Test",
+					Labels: map[string]string{
+						"traefik.tcp.services.foo.loadbalancer.server.port":      "8080",
+						"traefik.tcp.services.foo.loadbalancer.terminationdelay": "200",
+					},
+					NetworkSettings: networkSettings{
+						Ports: nat.PortMap{
+							nat.Port("80/tcp"): []nat.PortBinding{},
+						},
+						Networks: map[string]*networkData{
+							"bridge": {
+								Name: "bridge",
+								Addr: "127.0.0.1",
+							},
+						},
+					},
+				},
+			},
+			expected: &dynamic.Configuration{
+				TCP: &dynamic.TCPConfiguration{
+					Routers: map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{
+						"foo": {
+							LoadBalancer: &dynamic.TCPLoadBalancerService{
+								Servers: []dynamic.TCPServer{
+									{
+										Address: "127.0.0.1:8080",
+									},
+								},
+								TerminationDelay: Int(200),
 							},
 						},
 					},

pkg/provider/marathon/config.go

@@ -141,6 +141,7 @@ func (p *Provider) buildTCPServiceConfiguration(ctx context.Context, app maratho
 	if len(conf.Services) == 0 {
 		conf.Services = make(map[string]*dynamic.TCPService)
 		lb := &dynamic.TCPLoadBalancerService{}
+		lb.SetDefaults()
 		conf.Services[appName] = &dynamic.TCPService{
 			LoadBalancer: lb,
 		}

pkg/provider/marathon/config_test.go

@@ -11,6 +11,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func Int(v int) *int { return &v }
+
 func TestGetConfigurationAPIErrors(t *testing.T) {
 	fakeClient := newFakeClient(true, marathon.Applications{})
 
@@ -1240,6 +1242,7 @@ func TestBuildConfiguration(t *testing.T) {
 										Address: "localhost:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -1271,6 +1274,7 @@ func TestBuildConfiguration(t *testing.T) {
 										Address: "localhost:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -1310,6 +1314,48 @@ func TestBuildConfiguration(t *testing.T) {
 										Address: "localhost:8080",
 									},
 								},
+								TerminationDelay: Int(100),
+							},
+						},
+					},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+			},
+		},
+		{
+			desc: "one app with tcp labels with port, with termination delay",
+			applications: withApplications(
+				application(
+					appID("/app"),
+					appPorts(80, 81),
+					withTasks(localhostTask(taskPorts(80, 81))),
+					withLabel("traefik.tcp.routers.foo.rule", "HostSNI(`foo.bar`)"),
+					withLabel("traefik.tcp.routers.foo.tls", "true"),
+					withLabel("traefik.tcp.services.foo.loadbalancer.server.port", "8080"),
+					withLabel("traefik.tcp.services.foo.loadbalancer.terminationdelay", "200"),
+				)),
+			expected: &dynamic.Configuration{
+				TCP: &dynamic.TCPConfiguration{
+					Routers: map[string]*dynamic.TCPRouter{
+						"foo": {
+							Service: "foo",
+							Rule:    "HostSNI(`foo.bar`)",
+							TLS:     &dynamic.RouterTCPTLSConfig{},
+						},
+					},
+					Services: map[string]*dynamic.TCPService{
+						"foo": {
+							LoadBalancer: &dynamic.TCPLoadBalancerService{
+								Servers: []dynamic.TCPServer{
+									{
+										Address: "localhost:8080",
+									},
+								},
+								TerminationDelay: Int(200),
 							},
 						},
 					},
@@ -1350,6 +1396,7 @@ func TestBuildConfiguration(t *testing.T) {
 										Address: "localhost:8080",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},

pkg/provider/rancher/config.go

@@ -75,6 +75,7 @@ func (p *Provider) buildTCPServiceConfiguration(ctx context.Context, service ran
 	if len(configuration.Services) == 0 {
 		configuration.Services = make(map[string]*dynamic.TCPService)
 		lb := &dynamic.TCPLoadBalancerService{}
+		lb.SetDefaults()
 		configuration.Services[serviceName] = &dynamic.TCPService{
 			LoadBalancer: lb,
 		}

pkg/provider/rancher/config_test.go

@@ -9,6 +9,8 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func Int(v int) *int { return &v }
+
 func Test_buildConfiguration(t *testing.T) {
 	testCases := []struct {
 		desc        string
@@ -512,6 +514,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -548,6 +551,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:80",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -590,6 +594,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:8080",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -638,6 +643,7 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.2:8080",
 									},
 								},
+								TerminationDelay: Int(100),
 							},
 						},
 					},
@@ -693,6 +699,45 @@ func Test_buildConfiguration(t *testing.T) {
 										Address: "127.0.0.1:8080",
 									},
 								},
+								TerminationDelay: Int(100),
+							},
+						},
+					},
+				},
+				HTTP: &dynamic.HTTPConfiguration{
+					Routers:     map[string]*dynamic.Router{},
+					Middlewares: map[string]*dynamic.Middleware{},
+					Services:    map[string]*dynamic.Service{},
+				},
+			},
+		},
+		{
+			desc: "tcp with label for tcp service, with termination delay",
+			containers: []rancherData{
+				{
+					Name: "Test",
+					Labels: map[string]string{
+						"traefik.tcp.services.foo.loadbalancer.server.port":      "8080",
+						"traefik.tcp.services.foo.loadbalancer.terminationdelay": "200",
+					},
+					Port:       "80/tcp",
+					Containers: []string{"127.0.0.1"},
+					Health:     "",
+					State:      "",
+				},
+			},
+			expected: &dynamic.Configuration{
+				TCP: &dynamic.TCPConfiguration{
+					Routers: map[string]*dynamic.TCPRouter{},
+					Services: map[string]*dynamic.TCPService{
+						"foo": {
+							LoadBalancer: &dynamic.TCPLoadBalancerService{
+								Servers: []dynamic.TCPServer{
+									{
+										Address: "127.0.0.1:8080",
+									},
+								},
+								TerminationDelay: Int(200),
 							},
 						},
 					},

pkg/server/server_entrypoint_tcp.go

@@ -37,7 +37,7 @@ func newHTTPForwarder(ln net.Listener) *httpForwarder {
 }
 
 // ServeTCP uses the connection to serve it later in "Accept"
-func (h *httpForwarder) ServeTCP(conn net.Conn) {
+func (h *httpForwarder) ServeTCP(conn tcp.WriteCloser) {
 	h.connChan <- conn
 }
 
@@ -99,7 +99,36 @@ func NewTCPEntryPoint(ctx context.Context, configuration *static.EntryPoint) (*T
 	}, nil
 }
 
+// writeCloserWrapper wraps together a connection, and the concrete underlying
+// connection type that was found to satisfy WriteCloser.
+type writeCloserWrapper struct {
+	net.Conn
+	writeCloser tcp.WriteCloser
+}
+
+func (c *writeCloserWrapper) CloseWrite() error {
+	return c.writeCloser.CloseWrite()
+}
+
+// writeCloser returns the given connection, augmented with the WriteCloser
+// implementation, if any was found within the underlying conn.
+func writeCloser(conn net.Conn) (tcp.WriteCloser, error) {
+	switch typedConn := conn.(type) {
+	case *proxyprotocol.Conn:
+		underlying, err := writeCloser(typedConn.Conn)
+		if err != nil {
+			return nil, err
+		}
+		return &writeCloserWrapper{writeCloser: underlying, Conn: typedConn}, nil
+	case *net.TCPConn:
+		return typedConn, nil
+	default:
+		return nil, fmt.Errorf("unknown connection type %T", typedConn)
+	}
+}
+
 func (e *TCPEntryPoint) startTCP(ctx context.Context) {
+
 	log.FromContext(ctx).Debugf("Start TCP Server")
 
 	for {
@@ -109,8 +138,13 @@ func (e *TCPEntryPoint) startTCP(ctx context.Context) {
 			return
 		}
 
+		writeCloser, err := writeCloser(conn)
+		if err != nil {
+			panic(err)
+		}
+
 		safe.Go(func() {
-			e.switcher.ServeTCP(newTrackedConnection(conn, e.tracker))
+			e.switcher.ServeTCP(newTrackedConnection(writeCloser, e.tracker))
 		})
 	}
 }
@@ -374,20 +408,20 @@ func createHTTPServer(ln net.Listener, configuration *static.EntryPoint, withH2c
 	}, nil
 }
 
-func newTrackedConnection(conn net.Conn, tracker *connectionTracker) *trackedConnection {
+func newTrackedConnection(conn tcp.WriteCloser, tracker *connectionTracker) *trackedConnection {
 	tracker.AddConnection(conn)
 	return &trackedConnection{
-		Conn:    conn,
-		tracker: tracker,
+		WriteCloser: conn,
+		tracker:     tracker,
 	}
 }
 
 type trackedConnection struct {
 	tracker *connectionTracker
-	net.Conn
+	tcp.WriteCloser
 }
 
 func (t *trackedConnection) Close() error {
-	t.tracker.RemoveConnection(t.Conn)
-	return t.Conn.Close()
+	t.tracker.RemoveConnection(t.WriteCloser)
+	return t.WriteCloser.Close()
 }

pkg/server/server_entrypoint_tcp_test.go

@@ -113,7 +113,7 @@ func TestShutdownTCPConn(t *testing.T) {
 	go entryPoint.startTCP(context.Background())
 
 	router := &tcp.Router{}
-	router.AddCatchAllNoTLS(tcp.HandlerFunc(func(conn net.Conn) {
+	router.AddCatchAllNoTLS(tcp.HandlerFunc(func(conn tcp.WriteCloser) {
 		_, err := http.ReadRequest(bufio.NewReader(conn))
 		require.NoError(t, err)
 		time.Sleep(1 * time.Second)

pkg/server/service/tcp/service.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"time"
 
 	"github.com/containous/traefik/v2/pkg/config/runtime"
 	"github.com/containous/traefik/v2/pkg/log"
@@ -44,13 +45,19 @@ func (m *Manager) BuildTCP(rootCtx context.Context, serviceName string) (tcp.Han
 
 	loadBalancer := tcp.NewRRLoadBalancer()
 
+	if conf.LoadBalancer.TerminationDelay == nil {
+		defaultTerminationDelay := 100
+		conf.LoadBalancer.TerminationDelay = &defaultTerminationDelay
+	}
+	duration := time.Millisecond * time.Duration(*conf.LoadBalancer.TerminationDelay)
+
 	for name, server := range conf.LoadBalancer.Servers {
 		if _, _, err := net.SplitHostPort(server.Address); err != nil {
 			logger.Errorf("In service %q: %v", serviceQualifiedName, err)
 			continue
 		}
 
-		handler, err := tcp.NewProxy(server.Address)
+		handler, err := tcp.NewProxy(server.Address, duration)
 		if err != nil {
 			logger.Errorf("In service %q server %q: %v", serviceQualifiedName, server.Address, err)
 			continue

pkg/tcp/handler.go

@@ -6,14 +6,23 @@ import (
 
 // Handler is the TCP Handlers interface
 type Handler interface {
-	ServeTCP(conn net.Conn)
+	ServeTCP(conn WriteCloser)
 }
 
 // The HandlerFunc type is an adapter to allow the use of
 // ordinary functions as handlers.
-type HandlerFunc func(conn net.Conn)
+type HandlerFunc func(conn WriteCloser)
 
 // ServeTCP serves tcp
-func (f HandlerFunc) ServeTCP(conn net.Conn) {
+func (f HandlerFunc) ServeTCP(conn WriteCloser) {
 	f(conn)
 }
+
+// WriteCloser describes a net.Conn with a CloseWrite method.
+type WriteCloser interface {
+	net.Conn
+	// CloseWrite on a network connection, indicates that the issuer of the call
+	// has terminated sending on that connection.
+	// It corresponds to sending a FIN packet.
+	CloseWrite() error
+}

pkg/tcp/proxy.go

@@ -3,28 +3,32 @@ package tcp
 import (
 	"io"
 	"net"
+	"time"
 
 	"github.com/containous/traefik/v2/pkg/log"
 )
 
 // Proxy forwards a TCP request to a TCP service
 type Proxy struct {
-	target *net.TCPAddr
+	target           *net.TCPAddr
+	terminationDelay time.Duration
 }
 
 // NewProxy creates a new Proxy
-func NewProxy(address string) (*Proxy, error) {
+func NewProxy(address string, terminationDelay time.Duration) (*Proxy, error) {
 	tcpAddr, err := net.ResolveTCPAddr("tcp", address)
 	if err != nil {
 		return nil, err
 	}
 
-	return &Proxy{target: tcpAddr}, nil
+	return &Proxy{target: tcpAddr, terminationDelay: terminationDelay}, nil
 }
 
 // ServeTCP forwards the connection to a service
-func (p *Proxy) ServeTCP(conn net.Conn) {
+func (p *Proxy) ServeTCP(conn WriteCloser) {
 	log.Debugf("Handling connection from %s", conn.RemoteAddr())
+
+	// needed because of e.g. server.trackedConnection
 	defer conn.Close()
 
 	connBackend, err := net.DialTCP("tcp", nil, p.target)
@@ -32,19 +36,35 @@ func (p *Proxy) ServeTCP(conn net.Conn) {
 		log.Errorf("Error while connection to backend: %v", err)
 		return
 	}
+
+	// maybe not needed, but just in case
 	defer connBackend.Close()
 
-	errChan := make(chan error, 1)
-	go connCopy(conn, connBackend, errChan)
-	go connCopy(connBackend, conn, errChan)
+	errChan := make(chan error)
+	go p.connCopy(conn, connBackend, errChan)
+	go p.connCopy(connBackend, conn, errChan)
 
 	err = <-errChan
 	if err != nil {
-		log.Errorf("Error during connection: %v", err)
+		log.WithoutContext().Errorf("Error during connection: %v", err)
 	}
+
+	<-errChan
 }
 
-func connCopy(dst, src net.Conn, errCh chan error) {
+func (p Proxy) connCopy(dst, src WriteCloser, errCh chan error) {
 	_, err := io.Copy(dst, src)
 	errCh <- err
+
+	errClose := dst.CloseWrite()
+	if errClose != nil {
+		log.WithoutContext().Errorf("Error while terminating connection: %v", errClose)
+	}
+
+	if p.terminationDelay >= 0 {
+		err := dst.SetReadDeadline(time.Now().Add(p.terminationDelay))
+		if err != nil {
+			log.WithoutContext().Errorf("Error while setting deadline: %v", err)
+		}
+	}
 }

pkg/tcp/proxy_test.go

@@ -0,0 +1,81 @@
+package tcp
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func fakeRedis(t *testing.T, listener net.Listener) {
+	for {
+		conn, err := listener.Accept()
+		fmt.Println("Accept on server")
+		require.NoError(t, err)
+		for {
+			withErr := false
+			buf := make([]byte, 64)
+			if _, err := conn.Read(buf); err != nil {
+				withErr = true
+			}
+
+			if string(buf[:4]) == "ping" {
+				time.Sleep(time.Millisecond * 1)
+				if _, err := conn.Write([]byte("PONG")); err != nil {
+					conn.Close()
+					return
+				}
+			}
+			if withErr {
+				conn.Close()
+				return
+			}
+		}
+	}
+}
+
+func TestCloseWrite(t *testing.T) {
+	backendListener, err := net.Listen("tcp", ":0")
+	require.NoError(t, err)
+
+	go fakeRedis(t, backendListener)
+	_, port, err := net.SplitHostPort(backendListener.Addr().String())
+	require.NoError(t, err)
+
+	proxy, err := NewProxy(":"+port, 10*time.Millisecond)
+	require.NoError(t, err)
+
+	proxyListener, err := net.Listen("tcp", ":0")
+	require.NoError(t, err)
+
+	go func() {
+		for {
+			conn, err := proxyListener.Accept()
+			require.NoError(t, err)
+			proxy.ServeTCP(conn.(*net.TCPConn))
+		}
+	}()
+
+	_, port, err = net.SplitHostPort(proxyListener.Addr().String())
+	require.NoError(t, err)
+
+	conn, err := net.Dial("tcp", ":"+port)
+	require.NoError(t, err)
+
+	_, err = conn.Write([]byte("ping\n"))
+	require.NoError(t, err)
+
+	err = conn.(*net.TCPConn).CloseWrite()
+	require.NoError(t, err)
+
+	var buf []byte
+	buffer := bytes.NewBuffer(buf)
+	n, err := io.Copy(buffer, conn)
+	require.NoError(t, err)
+	require.Equal(t, int64(4), n)
+	require.Equal(t, "PONG", buffer.String())
+}

pkg/tcp/router.go

@@ -25,7 +25,7 @@ type Router struct {
 }
 
 // ServeTCP forwards the connection to the right TCP/HTTP handler
-func (r *Router) ServeTCP(conn net.Conn) {
+func (r *Router) ServeTCP(conn WriteCloser) {
 	// FIXME -- Check if ProxyProtocol changes the first bytes of the request
 
 	if r.catchAllNoTLS != nil && len(r.routingTable) == 0 && r.httpsHandler == nil {
@@ -99,11 +99,11 @@ func (r *Router) AddCatchAllNoTLS(handler Handler) {
 }
 
 // GetConn creates a connection proxy with a peeked string
-func (r *Router) GetConn(conn net.Conn, peeked string) net.Conn {
+func (r *Router) GetConn(conn WriteCloser, peeked string) WriteCloser {
 	// FIXME should it really be on Router ?
 	conn = &Conn{
-		Peeked: []byte(peeked),
-		Conn:   conn,
+		Peeked:      []byte(peeked),
+		WriteCloser: conn,
 	}
 	return conn
 }
@@ -157,7 +157,7 @@ type Conn struct {
 	// It can be type asserted against *net.TCPConn or other types
 	// as needed. It should not be read from directly unless
 	// Peeked is nil.
-	net.Conn
+	WriteCloser
 }
 
 // Read reads bytes from the connection (using the buffer prior to actually reading)
@@ -170,7 +170,7 @@ func (c *Conn) Read(p []byte) (n int, err error) {
 		}
 		return n, nil
 	}
-	return c.Conn.Read(p)
+	return c.WriteCloser.Read(p)
 }
 
 // clientHelloServerName returns the SNI server name inside the TLS ClientHello,

pkg/tcp/rr_load_balancer.go

@@ -1,7 +1,6 @@
 package tcp
 
 import (
-	"net"
 	"sync"
 
 	"github.com/containous/traefik/v2/pkg/log"
@@ -20,7 +19,7 @@ func NewRRLoadBalancer() *RRLoadBalancer {
 }
 
 // ServeTCP forwards the connection to the right service
-func (r *RRLoadBalancer) ServeTCP(conn net.Conn) {
+func (r *RRLoadBalancer) ServeTCP(conn WriteCloser) {
 	if len(r.servers) == 0 {
 		log.WithoutContext().Error("no available server")
 		return

pkg/tcp/switcher.go

@@ -1,8 +1,6 @@
 package tcp
 
 import (
-	"net"
-
 	"github.com/containous/traefik/v2/pkg/safe"
 )
 
@@ -12,7 +10,7 @@ type HandlerSwitcher struct {
 }
 
 // ServeTCP forwards the TCP connection to the current active handler
-func (s *HandlerSwitcher) ServeTCP(conn net.Conn) {
+func (s *HandlerSwitcher) ServeTCP(conn WriteCloser) {
 	handler := s.router.Get()
 	h, ok := handler.(Handler)
 	if ok {

pkg/tcp/tls.go

@@ -2,7 +2,6 @@ package tcp
 
 import (
 	"crypto/tls"
-	"net"
 )
 
 // TLSHandler handles TLS connections
@@ -12,6 +11,6 @@ type TLSHandler struct {
 }
 
 // ServeTCP terminates the TLS connection
-func (t *TLSHandler) ServeTCP(conn net.Conn) {
+func (t *TLSHandler) ServeTCP(conn WriteCloser) {
 	t.Next.ServeTCP(tls.Server(conn, t.Config))
 }