Introduce a fast proxy mode to improve HTTP/1.1 performances with backends

Co-authored-by: Romain <rtribotte@users.noreply.github.com>
Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>

.golangci.yml

@@ -229,7 +229,7 @@ issues:
       text: 'struct-tag: unknown option ''inline'' in JSON tag'
       linters:
         - revive
-    - path: pkg/server/service/bufferpool.go
+    - path: pkg/proxy/httputil/bufferpool.go
       text: 'SA6002: argument should be pointer-like to avoid allocations'
     - path: pkg/server/middleware/middlewares.go
       text: "Function 'buildConstructor' has too many statements"

cmd/traefik/traefik.go

@@ -37,6 +37,8 @@ import (
 	"github.com/traefik/traefik/v3/pkg/provider/aggregator"
 	"github.com/traefik/traefik/v3/pkg/provider/tailscale"
 	"github.com/traefik/traefik/v3/pkg/provider/traefik"
+	"github.com/traefik/traefik/v3/pkg/proxy"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
 	"github.com/traefik/traefik/v3/pkg/safe"
 	"github.com/traefik/traefik/v3/pkg/server"
 	"github.com/traefik/traefik/v3/pkg/server/middleware"
@@ -281,10 +283,16 @@ func setupServer(staticConfiguration *static.Configuration) (*server.Server, err
 		log.Info().Msg("Successfully obtained SPIFFE SVID.")
 	}
 
-	roundTripperManager := service.NewRoundTripperManager(spiffeX509Source)
+	transportManager := service.NewTransportManager(spiffeX509Source)
+
+	var proxyBuilder service.ProxyBuilder = httputil.NewProxyBuilder(transportManager, semConvMetricRegistry)
+	if staticConfiguration.Experimental != nil && staticConfiguration.Experimental.FastProxy != nil {
+		proxyBuilder = proxy.NewSmartBuilder(transportManager, proxyBuilder, *staticConfiguration.Experimental.FastProxy)
+	}
+
 	dialerManager := tcp.NewDialerManager(spiffeX509Source)
 	acmeHTTPHandler := getHTTPChallengeHandler(acmeProviders, httpChallengeProvider)
-	managerFactory := service.NewManagerFactory(*staticConfiguration, routinesPool, observabilityMgr, roundTripperManager, acmeHTTPHandler)
+	managerFactory := service.NewManagerFactory(*staticConfiguration, routinesPool, observabilityMgr, transportManager, proxyBuilder, acmeHTTPHandler)
 
 	// Router factory
 
@@ -318,7 +326,8 @@ func setupServer(staticConfiguration *static.Configuration) (*server.Server, err
 
 	// Server Transports
 	watcher.AddListener(func(conf dynamic.Configuration) {
-		roundTripperManager.Update(conf.HTTP.ServersTransports)
+		transportManager.Update(conf.HTTP.ServersTransports)
+		proxyBuilder.Update(conf.HTTP.ServersTransports)
 		dialerManager.Update(conf.TCP.ServersTransports)
 	})
 

docs/content/reference/static-configuration/cli-ref.md

@@ -228,6 +228,12 @@ WriteTimeout is the maximum duration before timing out writes of the response. I
 `--entrypoints.<name>.udp.timeout`:  
 Timeout defines how long to wait on an idle session before releasing the related resources. (Default: ```3```)
 
+`--experimental.fastproxy`:  
+Enable the FastProxy implementation. (Default: ```false```)
+
+`--experimental.fastproxy.debug`:  
+Enable debug mode for the FastProxy implementation. (Default: ```false```)
+
 `--experimental.kubernetesgateway`:  
 (Deprecated) Allow the Kubernetes gateway api provider usage. (Default: ```false```)
 

docs/content/reference/static-configuration/env-ref.md

@@ -228,6 +228,12 @@ WriteTimeout is the maximum duration before timing out writes of the response. I
 `TRAEFIK_ENTRYPOINTS_<NAME>_UDP_TIMEOUT`:  
 Timeout defines how long to wait on an idle session before releasing the related resources. (Default: ```3```)
 
+`TRAEFIK_EXPERIMENTAL_FASTPROXY`:  
+Enable the FastProxy implementation. (Default: ```false```)
+
+`TRAEFIK_EXPERIMENTAL_FASTPROXY_DEBUG`:  
+Enable debug mode for the FastProxy implementation. (Default: ```false```)
+
 `TRAEFIK_EXPERIMENTAL_KUBERNETESGATEWAY`:  
 (Deprecated) Allow the Kubernetes gateway api provider usage. (Default: ```false```)
 

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

@@ -509,6 +509,8 @@
       [experimental.localPlugins.LocalDescriptor1.settings]
         envs = ["foobar", "foobar"]
         mounts = ["foobar", "foobar"]
+  [experimental.fastProxy]
+    debug = true
 
 [core]
   defaultRuleSyntax = "foobar"

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

@@ -572,6 +572,8 @@ experimental:
         mounts:
           - foobar
           - foobar
+  fastProxy:
+    debug: true
   kubernetesGateway: true
 core:
   defaultRuleSyntax: foobar

docs/content/user-guides/fastproxy.md

@@ -0,0 +1,41 @@
+---
+title: "Traefik FastProxy Experimental Configuration"
+description: "This section of the Traefik Proxy documentation explains how to use the new FastProxy option."
+---
+
+# Traefik FastProxy Experimental Configuration
+
+## Overview
+
+This guide provides instructions on how to configure and use the new experimental `fastProxy` static configuration option in Traefik.
+The `fastProxy` option introduces a high-performance reverse proxy designed to enhance the performance of routing.
+
+!!! info "Limitations"
+
+    Please note that the new fast proxy implementation does not work with HTTP/2.
+    This means that when a H2C or HTTPS request with [HTTP2 enabled](../routing/services/index.md#disablehttp2) is sent to a backend, the fallback proxy is the regular one.
+
+    Additionnaly, observability features like tracing and OTEL semconv metrics are not supported for the moment.
+
+!!! warning "Experimental"
+    
+    The `fastProxy` option is currently experimental and subject to change in future releases. 
+    Use with caution in production environments.
+
+### Enabling FastProxy
+
+The fastProxy option is a static configuration parameter.
+To enable it, you need to configure it in your Traefik static configuration
+
+```yaml tab="File (YAML)"
+experimental:
+  fastProxy: {}
+```
+
+```toml tab="File (TOML)"
+[experimental.fastProxy]
+```
+
+```bash tab="CLI"
+--experimental.fastProxy
+```

docs/mkdocs.yml

@@ -163,6 +163,7 @@ nav:
           - 'Overview': 'observability/tracing/overview.md'
           - 'OpenTelemetry': 'observability/tracing/opentelemetry.md'
   - 'User Guides':
+      - 'FastProxy': 'user-guides/fastproxy.md'
       - 'Kubernetes and Let''s Encrypt': 'user-guides/crd-acme/index.md'
       - 'gRPC Examples': 'user-guides/grpc.md'
       - 'Docker':

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/BurntSushi/toml v1.4.0
 	github.com/Masterminds/sprig/v3 v3.2.3
 	github.com/abbot/go-http-auth v0.0.0-00010101000000-000000000000 // No tag on the repo.
-	github.com/andybalholm/brotli v1.0.6
+	github.com/andybalholm/brotli v1.1.0
 	github.com/aws/aws-sdk-go v1.44.327
 	github.com/cenkalti/backoff/v4 v4.3.0
 	github.com/containous/alice v0.0.0-20181107144136-d83ebdd94cbd // No tag on the repo.
@@ -102,6 +102,11 @@ require (
 	sigs.k8s.io/yaml v1.4.0
 )
 
+require (
+	github.com/armon/go-socks5 v0.0.0-20160902184237-e75332964ef5
+	github.com/valyala/fasthttp v1.55.0
+)
+
 require (
 	cloud.google.com/go/compute/metadata v0.3.0 // indirect
 	dario.cat/mergo v1.0.0 // indirect
@@ -315,6 +320,7 @@ require (
 	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/transip/gotransip/v6 v6.23.0 // indirect
 	github.com/ultradns/ultradns-go-sdk v1.6.1-20231103022937-8589b6a // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
 	github.com/vinyldns/go-vinyldns v0.9.16 // indirect
 	github.com/vultr/govultr/v3 v3.9.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect

go.sum

@@ -98,8 +98,8 @@ github.com/alecthomas/units v0.0.0-20151022065526-2efee857e7cf/go.mod h1:ybxpYRF
 github.com/alecthomas/units v0.0.0-20190717042225-c3de453c63f4/go.mod h1:ybxpYRFXyAe+OPACYpWeL0wqObRcbAqCMya13uyzqw0=
 github.com/aliyun/alibaba-cloud-sdk-go v1.62.712 h1:lM7JnA9dEdDFH9XOgRNQMDTQnOjlLkDTNA7c0aWTQ30=
 github.com/aliyun/alibaba-cloud-sdk-go v1.62.712/go.mod h1:SOSDHfe1kX91v3W5QiBsWSLqeLxImobbMX1mxrFHsVQ=
-github.com/andybalholm/brotli v1.0.6 h1:Yf9fFpf49Zrxb9NlQaluyE92/+X7UVHlhMNJN2sxfOI=
+github.com/andybalholm/brotli v1.1.0 h1:eLKJA0d02Lf0mVpIDgYnqXcUn0GqVmEFny3VuID1U3M=
-github.com/andybalholm/brotli v1.0.6/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
+github.com/andybalholm/brotli v1.1.0/go.mod h1:sms7XGricyQI9K10gOSf56VKKWS4oLer58Q+mhRPtnY=
 github.com/antihax/optional v1.0.0/go.mod h1:uupD/76wgC+ih3iEmQUL+0Ugr19nfwCT1kdvxnR2qWY=
 github.com/armon/circbuf v0.0.0-20150827004946-bbbad097214e/go.mod h1:3U/XgcO3hCbHZ8TKRvWD2dDTCfh9M9ya+I9JpbB7O8o=
 github.com/armon/go-metrics v0.0.0-20180917152333-f0300d1749da/go.mod h1:Q73ZrmVTwzkszR9V5SSuryQ31EELlFMUz1kKyl939pY=
@@ -1041,7 +1041,10 @@ github.com/unrolled/secure v1.0.9 h1:BWRuEb1vDrBFFDdbCnKkof3gZ35I/bnHGyt0LB0TNyQ
 github.com/unrolled/secure v1.0.9/go.mod h1:fO+mEan+FLB0CdEnHf6Q4ZZVNqG+5fuLFnP8p0BXDPI=
 github.com/urfave/negroni v1.0.0 h1:kIimOitoypq34K7TG7DUaJ9kq/N4Ofuwi1sjz0KipXc=
 github.com/urfave/negroni v1.0.0/go.mod h1:Meg73S6kFm/4PpbYdq35yYWoCZ9mS/YSx+lKnmiohz4=
+github.com/valyala/bytebufferpool v1.0.0 h1:GqA5TC/0021Y/b9FG4Oi9Mr3q7XYx6KllzawFIhcdPw=
 github.com/valyala/bytebufferpool v1.0.0/go.mod h1:6bBcMArwyJ5K/AmCkWv1jt77kVWyCJ6HpOuEn7z0Csc=
+github.com/valyala/fasthttp v1.55.0 h1:Zkefzgt6a7+bVKHnu/YaYSOPfNYNisSVBo/unVCf8k8=
+github.com/valyala/fasthttp v1.55.0/go.mod h1:NkY9JtkrpPKmgwV3HTaS2HWaJss9RSIsRVfcxxoHiOM=
 github.com/valyala/fasttemplate v1.0.1/go.mod h1:UQGH1tvbgY+Nz5t2n7tXsz52dQxojPUpymEIMZ47gx8=
 github.com/valyala/fasttemplate v1.2.1/go.mod h1:KHLXt3tVN2HBp8eijSv/kGJopbvo7S+qRAEEKiv+SiQ=
 github.com/vinyldns/go-vinyldns v0.9.16 h1:GZJStDkcCk1F1AcRc64LuuMh+ENL8pHA0CVd4ulRMcQ=

integration/fixtures/simple_fastproxy.toml

@@ -0,0 +1,35 @@
+[global]
+  checkNewVersion = false
+  sendAnonymousUsage = false
+
+[log]
+  level = "DEBUG"
+  noColor = true
+
+[entryPoints]
+  [entryPoints.web]
+    address = ":8000"
+
+[api]
+  insecure = true
+
+[providers.file]
+  filename = "{{ .SelfFilename }}"
+
+[experimental]
+  [experimental.fastProxy]
+    debug = true
+
+## dynamic configuration ##
+
+[http.routers]
+  [http.routers.router1]
+    entrypoints = ["web"]
+    service = "service1"
+    rule = "PathPrefix(`/`)"
+
+[http.services]
+  [http.services.service1]
+    [http.services.service1.loadBalancer]
+      [[http.services.service1.loadBalancer.servers]]
+        url = "{{ .Server }}"

integration/simple_test.go

@@ -65,6 +65,32 @@ func (s *SimpleSuite) TestSimpleDefaultConfig() {
 	require.NoError(s.T(), err)
 }
 
+func (s *SimpleSuite) TestSimpleFastProxy() {
+	var callCount int
+	srv1 := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		assert.Contains(s.T(), req.Header, "X-Traefik-Fast-Proxy")
+		callCount++
+	}))
+	defer srv1.Close()
+
+	file := s.adaptFile("fixtures/simple_fastproxy.toml", struct {
+		Server string
+	}{
+		Server: srv1.URL,
+	})
+
+	s.traefikCmd(withConfigFile(file), "--log.level=DEBUG")
+
+	// wait for traefik
+	err := try.GetRequest("http://127.0.0.1:8080/api/rawdata", 10*time.Second, try.BodyContains("127.0.0.1"))
+	require.NoError(s.T(), err)
+
+	err = try.GetRequest("http://127.0.0.1:8000/", time.Second)
+	require.NoError(s.T(), err)
+
+	assert.GreaterOrEqual(s.T(), 1, callCount)
+}
+
 func (s *SimpleSuite) TestWithWebConfig() {
 	s.cmdTraefik(withConfigFile("fixtures/simple_web.toml"))
 

pkg/config/static/experimental.go

@@ -7,6 +7,13 @@ type Experimental struct {
 	Plugins      map[string]plugins.Descriptor      `description:"Plugins configuration." json:"plugins,omitempty" toml:"plugins,omitempty" yaml:"plugins,omitempty" export:"true"`
 	LocalPlugins map[string]plugins.LocalDescriptor `description:"Local plugins configuration." json:"localPlugins,omitempty" toml:"localPlugins,omitempty" yaml:"localPlugins,omitempty" export:"true"`
 
+	FastProxy *FastProxyConfig `description:"Enable the FastProxy implementation." json:"fastProxy,omitempty" toml:"fastProxy,omitempty" yaml:"fastProxy,omitempty" label:"allowEmpty" file:"allowEmpty" export:"true"`
+
 	// Deprecated: KubernetesGateway provider is not an experimental feature starting with v3.1. Please remove its usage from the static configuration.
 	KubernetesGateway bool `description:"(Deprecated) Allow the Kubernetes gateway api provider usage." json:"kubernetesGateway,omitempty" toml:"kubernetesGateway,omitempty" yaml:"kubernetesGateway,omitempty" export:"true"`
 }
+
+// FastProxyConfig holds the FastProxy configuration.
+type FastProxyConfig struct {
+	Debug bool `description:"Enable debug mode for the FastProxy implementation." json:"debug,omitempty" toml:"debug,omitempty" yaml:"debug,omitempty" export:"true"`
+}

pkg/proxy/fast/builder.go

@@ -0,0 +1,129 @@
+package fast
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net"
+	"net/http"
+	"net/url"
+	"reflect"
+	"time"
+
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/config/static"
+)
+
+// TransportManager manages transport used for backend communications.
+type TransportManager interface {
+	Get(name string) (*dynamic.ServersTransport, error)
+	GetTLSConfig(name string) (*tls.Config, error)
+}
+
+// ProxyBuilder handles the connection pools for the FastProxy proxies.
+type ProxyBuilder struct {
+	debug            bool
+	transportManager TransportManager
+
+	// lock isn't needed because ProxyBuilder is not called concurrently.
+	pools map[string]map[string]*connPool
+	proxy func(*http.Request) (*url.URL, error)
+
+	// not goroutine safe.
+	configs map[string]*dynamic.ServersTransport
+}
+
+// NewProxyBuilder creates a new ProxyBuilder.
+func NewProxyBuilder(transportManager TransportManager, config static.FastProxyConfig) *ProxyBuilder {
+	return &ProxyBuilder{
+		debug:            config.Debug,
+		transportManager: transportManager,
+		pools:            make(map[string]map[string]*connPool),
+		proxy:            http.ProxyFromEnvironment,
+		configs:          make(map[string]*dynamic.ServersTransport),
+	}
+}
+
+// Update updates all the round-tripper corresponding to the given configs.
+// This method must not be used concurrently.
+func (r *ProxyBuilder) Update(newConfigs map[string]*dynamic.ServersTransport) {
+	for configName := range r.configs {
+		if _, ok := newConfigs[configName]; !ok {
+			for _, c := range r.pools[configName] {
+				c.Close()
+			}
+			delete(r.pools, configName)
+		}
+	}
+
+	for newConfigName, newConfig := range newConfigs {
+		if !reflect.DeepEqual(newConfig, r.configs[newConfigName]) {
+			for _, c := range r.pools[newConfigName] {
+				c.Close()
+			}
+			delete(r.pools, newConfigName)
+		}
+	}
+
+	r.configs = newConfigs
+}
+
+// Build builds a new ReverseProxy with the given configuration.
+func (r *ProxyBuilder) Build(cfgName string, targetURL *url.URL, passHostHeader bool) (http.Handler, error) {
+	proxyURL, err := r.proxy(&http.Request{URL: targetURL})
+	if err != nil {
+		return nil, fmt.Errorf("getting proxy: %w", err)
+	}
+
+	cfg, err := r.transportManager.Get(cfgName)
+	if err != nil {
+		return nil, fmt.Errorf("getting ServersTransport: %w", err)
+	}
+
+	var responseHeaderTimeout time.Duration
+	if cfg.ForwardingTimeouts != nil {
+		responseHeaderTimeout = time.Duration(cfg.ForwardingTimeouts.ResponseHeaderTimeout)
+	}
+
+	tlsConfig, err := r.transportManager.GetTLSConfig(cfgName)
+	if err != nil {
+		return nil, fmt.Errorf("getting TLS config: %w", err)
+	}
+
+	pool := r.getPool(cfgName, cfg, tlsConfig, targetURL, proxyURL)
+	return NewReverseProxy(targetURL, proxyURL, r.debug, passHostHeader, responseHeaderTimeout, pool)
+}
+
+func (r *ProxyBuilder) getPool(cfgName string, config *dynamic.ServersTransport, tlsConfig *tls.Config, targetURL *url.URL, proxyURL *url.URL) *connPool {
+	pool, ok := r.pools[cfgName]
+	if !ok {
+		pool = make(map[string]*connPool)
+		r.pools[cfgName] = pool
+	}
+
+	if connPool, ok := pool[targetURL.String()]; ok {
+		return connPool
+	}
+
+	idleConnTimeout := 90 * time.Second
+	dialTimeout := 30 * time.Second
+	if config.ForwardingTimeouts != nil {
+		idleConnTimeout = time.Duration(config.ForwardingTimeouts.IdleConnTimeout)
+		dialTimeout = time.Duration(config.ForwardingTimeouts.DialTimeout)
+	}
+
+	proxyDialer := newDialer(dialerConfig{
+		DialKeepAlive: 0,
+		DialTimeout:   dialTimeout,
+		HTTP:          true,
+		TLS:           targetURL.Scheme == "https",
+		ProxyURL:      proxyURL,
+	}, tlsConfig)
+
+	connPool := newConnPool(config.MaxIdleConnsPerHost, idleConnTimeout, func() (net.Conn, error) {
+		return proxyDialer.Dial("tcp", addrFromURL(targetURL))
+	})
+
+	r.pools[cfgName][targetURL.String()] = connPool
+
+	return connPool
+}

pkg/proxy/fast/connpool.go

@@ -0,0 +1,163 @@
+package fast
+
+import (
+	"fmt"
+	"net"
+	"time"
+
+	"github.com/rs/zerolog/log"
+)
+
+// conn is an enriched net.Conn.
+type conn struct {
+	net.Conn
+
+	idleAt      time.Time // the last time it was marked as idle.
+	idleTimeout time.Duration
+}
+
+func (c *conn) isExpired() bool {
+	expTime := c.idleAt.Add(c.idleTimeout)
+	return c.idleTimeout > 0 && time.Now().After(expTime)
+}
+
+// connPool is a net.Conn pool implementation using channels.
+type connPool struct {
+	dialer          func() (net.Conn, error)
+	idleConns       chan *conn
+	idleConnTimeout time.Duration
+	ticker          *time.Ticker
+	doneCh          chan struct{}
+}
+
+// newConnPool creates a new connPool.
+func newConnPool(maxIdleConn int, idleConnTimeout time.Duration, dialer func() (net.Conn, error)) *connPool {
+	c := &connPool{
+		dialer:          dialer,
+		idleConns:       make(chan *conn, maxIdleConn),
+		idleConnTimeout: idleConnTimeout,
+		doneCh:          make(chan struct{}),
+	}
+
+	if idleConnTimeout > 0 {
+		c.ticker = time.NewTicker(c.idleConnTimeout / 2)
+		go func() {
+			for {
+				select {
+				case <-c.ticker.C:
+					c.cleanIdleConns()
+				case <-c.doneCh:
+					return
+				}
+			}
+		}()
+	}
+
+	return c
+}
+
+// Close closes stop the cleanIdleConn goroutine.
+func (c *connPool) Close() {
+	if c.idleConnTimeout > 0 {
+		close(c.doneCh)
+		c.ticker.Stop()
+	}
+}
+
+// AcquireConn returns an idle net.Conn from the pool.
+func (c *connPool) AcquireConn() (*conn, error) {
+	for {
+		co, err := c.acquireConn()
+		if err != nil {
+			return nil, err
+		}
+
+		if !co.isExpired() {
+			return co, nil
+		}
+
+		// As the acquired conn is expired we can close it
+		// without putting it again into the pool.
+		if err := co.Close(); err != nil {
+			log.Debug().
+				Err(err).
+				Msg("Unexpected error while releasing the connection")
+		}
+	}
+}
+
+// ReleaseConn releases the given net.Conn to the pool.
+func (c *connPool) ReleaseConn(co *conn) {
+	co.idleAt = time.Now()
+	c.releaseConn(co)
+}
+
+// cleanIdleConns is a routine cleaning the expired connections at a regular basis.
+func (c *connPool) cleanIdleConns() {
+	for {
+		select {
+		case co := <-c.idleConns:
+			if !co.isExpired() {
+				c.releaseConn(co)
+				return
+			}
+
+			if err := co.Close(); err != nil {
+				log.Debug().
+					Err(err).
+					Msg("Unexpected error while releasing the connection")
+			}
+
+		default:
+			return
+		}
+	}
+}
+
+func (c *connPool) acquireConn() (*conn, error) {
+	select {
+	case co := <-c.idleConns:
+		return co, nil
+
+	default:
+		errCh := make(chan error, 1)
+		go c.askForNewConn(errCh)
+
+		select {
+		case co := <-c.idleConns:
+			return co, nil
+
+		case err := <-errCh:
+			return nil, err
+		}
+	}
+}
+
+func (c *connPool) releaseConn(co *conn) {
+	select {
+	case c.idleConns <- co:
+
+	// Hitting the default case means that we have reached the maximum number of idle
+	// connections, so we can close it.
+	default:
+		if err := co.Close(); err != nil {
+			log.Debug().
+				Err(err).
+				Msg("Unexpected error while releasing the connection")
+		}
+	}
+}
+
+func (c *connPool) askForNewConn(errCh chan<- error) {
+	co, err := c.dialer()
+	if err != nil {
+		errCh <- fmt.Errorf("create conn: %w", err)
+		return
+	}
+
+	c.releaseConn(&conn{
+		Conn:        co,
+		idleAt:      time.Now(),
+		idleTimeout: c.idleConnTimeout,
+	})
+}

pkg/proxy/fast/connpool_test.go

@@ -0,0 +1,184 @@
+package fast
+
+import (
+	"net"
+	"runtime"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestConnPool_ConnReuse(t *testing.T) {
+	testCases := []struct {
+		desc     string
+		poolFn   func(pool *connPool)
+		expected int
+	}{
+		{
+			desc: "One connection",
+			poolFn: func(pool *connPool) {
+				c1, _ := pool.AcquireConn()
+				pool.ReleaseConn(c1)
+			},
+			expected: 1,
+		},
+		{
+			desc: "Two connections with release",
+			poolFn: func(pool *connPool) {
+				c1, _ := pool.AcquireConn()
+				pool.ReleaseConn(c1)
+
+				c2, _ := pool.AcquireConn()
+				pool.ReleaseConn(c2)
+			},
+			expected: 1,
+		},
+		{
+			desc: "Two concurrent connections",
+			poolFn: func(pool *connPool) {
+				c1, _ := pool.AcquireConn()
+				c2, _ := pool.AcquireConn()
+
+				pool.ReleaseConn(c1)
+				pool.ReleaseConn(c2)
+			},
+			expected: 2,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var connAlloc int
+			dialer := func() (net.Conn, error) {
+				connAlloc++
+				return &net.TCPConn{}, nil
+			}
+
+			pool := newConnPool(2, 0, dialer)
+			test.poolFn(pool)
+
+			assert.Equal(t, test.expected, connAlloc)
+		})
+	}
+}
+
+func TestConnPool_MaxIdleConn(t *testing.T) {
+	testCases := []struct {
+		desc        string
+		poolFn      func(pool *connPool)
+		maxIdleConn int
+		expected    int
+	}{
+		{
+			desc: "One connection",
+			poolFn: func(pool *connPool) {
+				c1, _ := pool.AcquireConn()
+				pool.ReleaseConn(c1)
+			},
+			maxIdleConn: 1,
+			expected:    1,
+		},
+		{
+			desc: "Multiple connections with defered release",
+			poolFn: func(pool *connPool) {
+				for range 7 {
+					c, _ := pool.AcquireConn()
+					defer pool.ReleaseConn(c)
+				}
+			},
+			maxIdleConn: 5,
+			expected:    5,
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var keepOpenedConn int
+			dialer := func() (net.Conn, error) {
+				keepOpenedConn++
+				return &mockConn{closeFn: func() error {
+					keepOpenedConn--
+					return nil
+				}}, nil
+			}
+
+			pool := newConnPool(test.maxIdleConn, 0, dialer)
+			test.poolFn(pool)
+
+			assert.Equal(t, test.expected, keepOpenedConn)
+		})
+	}
+}
+
+func TestGC(t *testing.T) {
+	var isDestroyed bool
+	pools := map[string]*connPool{}
+	dialer := func() (net.Conn, error) {
+		c := &mockConn{closeFn: func() error {
+			return nil
+		}}
+		return c, nil
+	}
+
+	pools["test"] = newConnPool(10, 1*time.Second, dialer)
+	runtime.SetFinalizer(pools["test"], func(p *connPool) {
+		isDestroyed = true
+	})
+	c, err := pools["test"].AcquireConn()
+	require.NoError(t, err)
+
+	pools["test"].ReleaseConn(c)
+
+	pools["test"].Close()
+
+	delete(pools, "test")
+
+	runtime.GC()
+
+	require.True(t, isDestroyed)
+}
+
+type mockConn struct {
+	closeFn func() error
+}
+
+func (m *mockConn) Read(_ []byte) (n int, err error) {
+	panic("implement me")
+}
+
+func (m *mockConn) Write(_ []byte) (n int, err error) {
+	panic("implement me")
+}
+
+func (m *mockConn) Close() error {
+	if m.closeFn != nil {
+		return m.closeFn()
+	}
+	return nil
+}
+
+func (m *mockConn) LocalAddr() net.Addr {
+	panic("implement me")
+}
+
+func (m *mockConn) RemoteAddr() net.Addr {
+	panic("implement me")
+}
+
+func (m *mockConn) SetDeadline(_ time.Time) error {
+	panic("implement me")
+}
+
+func (m *mockConn) SetReadDeadline(_ time.Time) error {
+	panic("implement me")
+}
+
+func (m *mockConn) SetWriteDeadline(_ time.Time) error {
+	panic("implement me")
+}

pkg/proxy/fast/dialer.go

@@ -0,0 +1,195 @@
+package fast
+
+import (
+	"bufio"
+	"context"
+	"crypto/tls"
+	"encoding/base64"
+	"errors"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+
+	"golang.org/x/net/proxy"
+)
+
+const (
+	schemeHTTP   = "http"
+	schemeHTTPS  = "https"
+	schemeSocks5 = "socks5"
+)
+
+type dialer interface {
+	Dial(network, addr string) (c net.Conn, err error)
+}
+
+type dialerFunc func(network, addr string) (net.Conn, error)
+
+func (d dialerFunc) Dial(network, addr string) (net.Conn, error) {
+	return d(network, addr)
+}
+
+type dialerConfig struct {
+	DialKeepAlive time.Duration
+	DialTimeout   time.Duration
+	ProxyURL      *url.URL
+	HTTP          bool
+	TLS           bool
+}
+
+func newDialer(cfg dialerConfig, tlsConfig *tls.Config) dialer {
+	if cfg.ProxyURL == nil {
+		return buildDialer(cfg, tlsConfig, cfg.TLS)
+	}
+
+	proxyDialer := buildDialer(cfg, tlsConfig, cfg.ProxyURL.Scheme == "https")
+	proxyAddr := addrFromURL(cfg.ProxyURL)
+
+	switch {
+	case cfg.ProxyURL.Scheme == schemeSocks5:
+		var auth *proxy.Auth
+		if u := cfg.ProxyURL.User; u != nil {
+			auth = &proxy.Auth{User: u.Username()}
+			auth.Password, _ = u.Password()
+		}
+
+		// SOCKS5 implementation do not return errors.
+		socksDialer, _ := proxy.SOCKS5("tcp", proxyAddr, auth, proxyDialer)
+		return dialerFunc(func(network, targetAddr string) (net.Conn, error) {
+			co, err := socksDialer.Dial("tcp", targetAddr)
+			if err != nil {
+				return nil, err
+			}
+
+			if cfg.TLS {
+				c := &tls.Config{}
+				if tlsConfig != nil {
+					c = tlsConfig.Clone()
+				}
+
+				if c.ServerName == "" {
+					host, _, _ := net.SplitHostPort(targetAddr)
+					c.ServerName = host
+				}
+
+				return tls.Client(co, c), nil
+			}
+
+			return co, nil
+		})
+	case cfg.HTTP && !cfg.TLS:
+		// Nothing to do the Proxy-Authorization header will be added by the ReverseProxy.
+
+	default:
+		hdr := make(http.Header)
+		if u := cfg.ProxyURL.User; u != nil {
+			username := u.Username()
+			password, _ := u.Password()
+			auth := username + ":" + password
+			hdr.Set("Proxy-Authorization", "Basic "+base64.StdEncoding.EncodeToString([]byte(auth)))
+		}
+
+		return dialerFunc(func(network, targetAddr string) (net.Conn, error) {
+			conn, err := proxyDialer.Dial("tcp", proxyAddr)
+			if err != nil {
+				return nil, err
+			}
+
+			connectReq := &http.Request{
+				Method: http.MethodConnect,
+				URL:    &url.URL{Opaque: targetAddr},
+				Host:   targetAddr,
+				Header: hdr,
+			}
+
+			connectCtx, cancel := context.WithTimeout(context.Background(), 1*time.Minute)
+			defer cancel()
+
+			didReadResponse := make(chan struct{}) // closed after CONNECT write+read is done or fails
+			var resp *http.Response
+
+			// Write the CONNECT request & read the response.
+			go func() {
+				defer close(didReadResponse)
+				err = connectReq.Write(conn)
+				if err != nil {
+					return
+				}
+				// Okay to use and discard buffered reader here, because
+				// TLS server will not speak until spoken to.
+				br := bufio.NewReader(conn)
+				resp, err = http.ReadResponse(br, connectReq)
+			}()
+
+			select {
+			case <-connectCtx.Done():
+				conn.Close()
+				<-didReadResponse
+				return nil, connectCtx.Err()
+			case <-didReadResponse:
+				// resp or err now set
+			}
+			if err != nil {
+				conn.Close()
+				return nil, err
+			}
+
+			if resp.StatusCode != http.StatusOK {
+				_, statusText, ok := strings.Cut(resp.Status, " ")
+				conn.Close()
+				if !ok {
+					return nil, errors.New("unknown status code")
+				}
+
+				return nil, errors.New(statusText)
+			}
+
+			c := &tls.Config{}
+			if tlsConfig != nil {
+				c = tlsConfig.Clone()
+			}
+			if c.ServerName == "" {
+				host, _, _ := net.SplitHostPort(targetAddr)
+				c.ServerName = host
+			}
+
+			return tls.Client(conn, c), nil
+		})
+	}
+	return dialerFunc(func(network, addr string) (net.Conn, error) {
+		return proxyDialer.Dial("tcp", proxyAddr)
+	})
+}
+
+func buildDialer(cfg dialerConfig, tlsConfig *tls.Config, isTLS bool) dialer {
+	dialer := &net.Dialer{
+		Timeout:   cfg.DialTimeout,
+		KeepAlive: cfg.DialKeepAlive,
+	}
+
+	if !isTLS {
+		return dialer
+	}
+
+	return &tls.Dialer{
+		NetDialer: dialer,
+		Config:    tlsConfig,
+	}
+}
+
+func addrFromURL(u *url.URL) string {
+	addr := u.Host
+
+	if u.Port() == "" {
+		switch u.Scheme {
+		case schemeHTTP:
+			return addr + ":80"
+		case schemeHTTPS:
+			return addr + ":443"
+		}
+	}
+
+	return addr
+}

pkg/proxy/fast/proxy.go

@@ -0,0 +1,553 @@
+package fast
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptrace"
+	"net/http/httputil"
+	"net/url"
+	"strings"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/rs/zerolog/log"
+	proxyhttputil "github.com/traefik/traefik/v3/pkg/proxy/httputil"
+	"github.com/valyala/fasthttp"
+	"golang.org/x/net/http/httpguts"
+)
+
+const (
+	bufferSize = 32 * 1024
+	bufioSize  = 64 * 1024
+)
+
+var hopHeaders = []string{
+	"Connection",
+	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
+	"Keep-Alive",
+	"Proxy-Authenticate",
+	"Proxy-Authorization",
+	"Te",      // canonicalized version of "TE"
+	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
+	"Transfer-Encoding",
+	"Upgrade",
+}
+
+type pool[T any] struct {
+	pool sync.Pool
+}
+
+func (p *pool[T]) Get() T {
+	if tmp := p.pool.Get(); tmp != nil {
+		return tmp.(T)
+	}
+
+	var res T
+	return res
+}
+
+func (p *pool[T]) Put(x T) {
+	p.pool.Put(x)
+}
+
+type buffConn struct {
+	*bufio.Reader
+	net.Conn
+}
+
+func (b buffConn) Read(p []byte) (int, error) {
+	return b.Reader.Read(p)
+}
+
+type writeDetector struct {
+	net.Conn
+
+	written bool
+}
+
+func (w *writeDetector) Write(p []byte) (int, error) {
+	n, err := w.Conn.Write(p)
+	if n > 0 {
+		w.written = true
+	}
+
+	return n, err
+}
+
+type writeFlusher struct {
+	io.Writer
+}
+
+func (w *writeFlusher) Write(b []byte) (int, error) {
+	n, err := w.Writer.Write(b)
+	if f, ok := w.Writer.(http.Flusher); ok {
+		f.Flush()
+	}
+
+	return n, err
+}
+
+type timeoutError struct {
+	error
+}
+
+func (t timeoutError) Timeout() bool {
+	return true
+}
+
+func (t timeoutError) Temporary() bool {
+	return false
+}
+
+// ReverseProxy is the FastProxy reverse proxy implementation.
+type ReverseProxy struct {
+	debug bool
+
+	connPool *connPool
+
+	bufferPool      pool[[]byte]
+	readerPool      pool[*bufio.Reader]
+	writerPool      pool[*bufio.Writer]
+	limitReaderPool pool[*io.LimitedReader]
+
+	proxyAuth string
+
+	targetURL             *url.URL
+	passHostHeader        bool
+	responseHeaderTimeout time.Duration
+}
+
+// NewReverseProxy creates a new ReverseProxy.
+func NewReverseProxy(targetURL *url.URL, proxyURL *url.URL, debug, passHostHeader bool, responseHeaderTimeout time.Duration, connPool *connPool) (*ReverseProxy, error) {
+	var proxyAuth string
+	if proxyURL != nil && proxyURL.User != nil && targetURL.Scheme == "http" {
+		username := proxyURL.User.Username()
+		password, _ := proxyURL.User.Password()
+		proxyAuth = "Basic " + base64.StdEncoding.EncodeToString([]byte(username+":"+password))
+	}
+
+	return &ReverseProxy{
+		debug:                 debug,
+		passHostHeader:        passHostHeader,
+		targetURL:             targetURL,
+		proxyAuth:             proxyAuth,
+		connPool:              connPool,
+		responseHeaderTimeout: responseHeaderTimeout,
+	}, nil
+}
+
+func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	if req.Body != nil {
+		defer req.Body.Close()
+	}
+
+	outReq := fasthttp.AcquireRequest()
+	defer fasthttp.ReleaseRequest(outReq)
+
+	// This is not required as the headers are already normalized by net/http.
+	outReq.Header.DisableNormalizing()
+
+	for k, v := range req.Header {
+		for _, s := range v {
+			outReq.Header.Add(k, s)
+		}
+	}
+
+	removeConnectionHeaders(&outReq.Header)
+
+	for _, header := range hopHeaders {
+		outReq.Header.Del(header)
+	}
+
+	if p.proxyAuth != "" {
+		outReq.Header.Set("Proxy-Authorization", p.proxyAuth)
+	}
+
+	if httpguts.HeaderValuesContainsToken(req.Header["Te"], "trailers") {
+		outReq.Header.Set("Te", "trailers")
+	}
+
+	if p.debug {
+		outReq.Header.Set("X-Traefik-Fast-Proxy", "enabled")
+	}
+
+	reqUpType := upgradeType(req.Header)
+	if !isGraphic(reqUpType) {
+		proxyhttputil.ErrorHandler(rw, req, fmt.Errorf("client tried to switch to invalid protocol %q", reqUpType))
+		return
+	}
+
+	if reqUpType != "" {
+		outReq.Header.Set("Connection", "Upgrade")
+		outReq.Header.Set("Upgrade", reqUpType)
+		if reqUpType == "websocket" {
+			cleanWebSocketHeaders(&outReq.Header)
+		}
+	}
+
+	u2 := new(url.URL)
+	*u2 = *req.URL
+	u2.Scheme = p.targetURL.Scheme
+	u2.Host = p.targetURL.Host
+
+	u := req.URL
+	if req.RequestURI != "" {
+		parsedURL, err := url.ParseRequestURI(req.RequestURI)
+		if err == nil {
+			u = parsedURL
+		}
+	}
+
+	u2.Path = u.Path
+	u2.RawPath = u.RawPath
+	u2.RawQuery = strings.ReplaceAll(u.RawQuery, ";", "&")
+
+	outReq.SetHost(u2.Host)
+	outReq.Header.SetHost(u2.Host)
+
+	if p.passHostHeader {
+		outReq.Header.SetHost(req.Host)
+	}
+
+	outReq.SetRequestURI(u2.RequestURI())
+
+	outReq.SetBodyStream(req.Body, int(req.ContentLength))
+
+	outReq.Header.SetMethod(req.Method)
+
+	if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
+		// If we aren't the first proxy retain prior
+		// X-Forwarded-For information as a comma+space
+		// separated list and fold multiple headers into one.
+		prior, ok := req.Header["X-Forwarded-For"]
+		if len(prior) > 0 {
+			clientIP = strings.Join(prior, ", ") + ", " + clientIP
+		}
+
+		omit := ok && prior == nil // Go Issue 38079: nil now means don't populate the header
+		if !omit {
+			outReq.Header.Set("X-Forwarded-For", clientIP)
+		}
+	}
+
+	if err := p.roundTrip(rw, req, outReq, reqUpType); err != nil {
+		proxyhttputil.ErrorHandler(rw, req, err)
+	}
+}
+
+// Note that unlike the net/http RoundTrip:
+//   - we are not supporting "100 Continue" response to forward them as-is to the client.
+//   - we are not asking for compressed response automatically. That is because this will add an extra cost when the
+//     client is asking for an uncompressed response, as we will have to un-compress it, and nowadays most clients are
+//     already asking for compressed response (allowing "passthrough" compression).
+func (p *ReverseProxy) roundTrip(rw http.ResponseWriter, req *http.Request, outReq *fasthttp.Request, reqUpType string) error {
+	ctx := req.Context()
+	trace := httptrace.ContextClientTrace(ctx)
+
+	var co *conn
+	for {
+		select {
+		case <-ctx.Done():
+			return ctx.Err()
+
+		default:
+		}
+
+		var err error
+		co, err = p.connPool.AcquireConn()
+		if err != nil {
+			return fmt.Errorf("acquire connection: %w", err)
+		}
+
+		wd := &writeDetector{Conn: co}
+
+		err = p.writeRequest(wd, outReq)
+		if wd.written && trace != nil && trace.WroteRequest != nil {
+			// WroteRequest hook is used by the tracing middleware to detect if the request has been written.
+			trace.WroteRequest(httptrace.WroteRequestInfo{})
+		}
+		if err == nil {
+			break
+		}
+
+		log.Ctx(ctx).Debug().Err(err).Msg("Error while writing request")
+
+		co.Close()
+
+		if wd.written && !isReplayable(req) {
+			return err
+		}
+	}
+
+	br := p.readerPool.Get()
+	if br == nil {
+		br = bufio.NewReaderSize(co, bufioSize)
+	}
+	defer p.readerPool.Put(br)
+
+	br.Reset(co)
+
+	res := fasthttp.AcquireResponse()
+	defer fasthttp.ReleaseResponse(res)
+
+	res.Header.SetNoDefaultContentType(true)
+
+	for {
+		var timer *time.Timer
+		errTimeout := atomic.Pointer[timeoutError]{}
+		if p.responseHeaderTimeout > 0 {
+			timer = time.AfterFunc(p.responseHeaderTimeout, func() {
+				errTimeout.Store(&timeoutError{errors.New("timeout awaiting response headers")})
+				co.Close()
+			})
+		}
+
+		res.Header.SetNoDefaultContentType(true)
+		if err := res.Header.Read(br); err != nil {
+			if p.responseHeaderTimeout > 0 {
+				if errT := errTimeout.Load(); errT != nil {
+					return errT
+				}
+			}
+			co.Close()
+			return err
+		}
+
+		if timer != nil {
+			timer.Stop()
+		}
+
+		fixPragmaCacheControl(&res.Header)
+
+		resCode := res.StatusCode()
+		is1xx := 100 <= resCode && resCode <= 199
+		// treat 101 as a terminal status, see issue 26161
+		is1xxNonTerminal := is1xx && resCode != http.StatusSwitchingProtocols
+		if is1xxNonTerminal {
+			removeConnectionHeaders(&res.Header)
+			h := rw.Header()
+
+			for _, header := range hopHeaders {
+				res.Header.Del(header)
+			}
+
+			res.Header.VisitAll(func(key, value []byte) {
+				rw.Header().Add(string(key), string(value))
+			})
+
+			rw.WriteHeader(res.StatusCode())
+			// Clear headers, it's not automatically done by ResponseWriter.WriteHeader() for 1xx responses
+			for k := range h {
+				delete(h, k)
+			}
+
+			res.Reset()
+			res.Header.Reset()
+			res.Header.SetNoDefaultContentType(true)
+
+			continue
+		}
+		break
+	}
+
+	announcedTrailers := res.Header.Peek("Trailer")
+
+	// Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
+	if res.StatusCode() == http.StatusSwitchingProtocols {
+		// As the connection has been hijacked, it cannot be added back to the pool.
+		handleUpgradeResponse(rw, req, reqUpType, res, buffConn{Conn: co, Reader: br})
+		return nil
+	}
+
+	removeConnectionHeaders(&res.Header)
+
+	for _, header := range hopHeaders {
+		res.Header.Del(header)
+	}
+
+	if len(announcedTrailers) > 0 {
+		res.Header.Add("Trailer", string(announcedTrailers))
+	}
+
+	res.Header.VisitAll(func(key, value []byte) {
+		rw.Header().Add(string(key), string(value))
+	})
+
+	rw.WriteHeader(res.StatusCode())
+
+	// Chunked response, Content-Length is set to -1 by FastProxy when "Transfer-Encoding: chunked" header is received.
+	if res.Header.ContentLength() == -1 {
+		cbr := httputil.NewChunkedReader(br)
+
+		b := p.bufferPool.Get()
+		if b == nil {
+			b = make([]byte, bufferSize)
+		}
+		defer p.bufferPool.Put(b)
+
+		if _, err := io.CopyBuffer(&writeFlusher{rw}, cbr, b); err != nil {
+			co.Close()
+			return err
+		}
+
+		res.Header.Reset()
+		res.Header.SetNoDefaultContentType(true)
+		if err := res.Header.ReadTrailer(br); err != nil {
+			co.Close()
+			return err
+		}
+
+		if res.Header.Len() > 0 {
+			var announcedTrailersKey []string
+			if len(announcedTrailers) > 0 {
+				announcedTrailersKey = strings.Split(string(announcedTrailers), ",")
+			}
+
+			res.Header.VisitAll(func(key, value []byte) {
+				for _, s := range announcedTrailersKey {
+					if strings.EqualFold(s, strings.TrimSpace(string(key))) {
+						rw.Header().Add(string(key), string(value))
+						return
+					}
+				}
+
+				rw.Header().Add(http.TrailerPrefix+string(key), string(value))
+			})
+		}
+
+		p.connPool.ReleaseConn(co)
+
+		return nil
+	}
+
+	brl := p.limitReaderPool.Get()
+	if brl == nil {
+		brl = &io.LimitedReader{}
+	}
+	defer p.limitReaderPool.Put(brl)
+
+	brl.R = br
+	brl.N = int64(res.Header.ContentLength())
+
+	b := p.bufferPool.Get()
+	if b == nil {
+		b = make([]byte, bufferSize)
+	}
+	defer p.bufferPool.Put(b)
+
+	if _, err := io.CopyBuffer(rw, brl, b); err != nil {
+		co.Close()
+		return err
+	}
+
+	p.connPool.ReleaseConn(co)
+
+	return nil
+}
+
+func (p *ReverseProxy) writeRequest(co net.Conn, outReq *fasthttp.Request) error {
+	bw := p.writerPool.Get()
+	if bw == nil {
+		bw = bufio.NewWriterSize(co, bufioSize)
+	}
+	defer p.writerPool.Put(bw)
+
+	bw.Reset(co)
+
+	if err := outReq.Write(bw); err != nil {
+		return err
+	}
+
+	return bw.Flush()
+}
+
+// isReplayable returns whether the request is replayable.
+func isReplayable(req *http.Request) bool {
+	if req.Body == nil || req.Body == http.NoBody {
+		switch req.Method {
+		case http.MethodGet, http.MethodHead, http.MethodOptions, http.MethodTrace:
+			return true
+		}
+
+		// The Idempotency-Key, while non-standard, is widely used to
+		// mean a POST or other request is idempotent. See
+		// https://golang.org/issue/19943#issuecomment-421092421
+		if _, ok := req.Header["Idempotency-Key"]; ok {
+			return true
+		}
+
+		if _, ok := req.Header["X-Idempotency-Key"]; ok {
+			return true
+		}
+	}
+
+	return false
+}
+
+// isGraphic returns whether s is ASCII and printable according to
+// https://tools.ietf.org/html/rfc20#section-4.2.
+func isGraphic(s string) bool {
+	for i := range len(s) {
+		if s[i] < ' ' || s[i] > '~' {
+			return false
+		}
+	}
+
+	return true
+}
+
+type fasthttpHeader interface {
+	Peek(key string) []byte
+	Set(key string, value string)
+	SetBytesV(key string, value []byte)
+	DelBytes(key []byte)
+	Del(key string)
+}
+
+// removeConnectionHeaders removes hop-by-hop headers listed in the "Connection" header of h.
+// See RFC 7230, section 6.1.
+func removeConnectionHeaders(h fasthttpHeader) {
+	f := h.Peek(fasthttp.HeaderConnection)
+	for _, sf := range bytes.Split(f, []byte{','}) {
+		if sf = bytes.TrimSpace(sf); len(sf) > 0 {
+			h.DelBytes(sf)
+		}
+	}
+}
+
+// RFC 7234, section 5.4: Should treat Pragma: no-cache like Cache-Control: no-cache.
+func fixPragmaCacheControl(header fasthttpHeader) {
+	if pragma := header.Peek("Pragma"); bytes.Equal(pragma, []byte("no-cache")) {
+		if len(header.Peek("Cache-Control")) == 0 {
+			header.Set("Cache-Control", "no-cache")
+		}
+	}
+}
+
+// cleanWebSocketHeaders Even if the websocket RFC says that headers should be case-insensitive,
+// some servers need Sec-WebSocket-Key, Sec-WebSocket-Extensions, Sec-WebSocket-Accept,
+// Sec-WebSocket-Protocol and Sec-WebSocket-Version to be case-sensitive.
+// https://tools.ietf.org/html/rfc6455#page-20
+func cleanWebSocketHeaders(headers fasthttpHeader) {
+	headers.SetBytesV("Sec-WebSocket-Key", headers.Peek("Sec-Websocket-Key"))
+	headers.Del("Sec-Websocket-Key")
+
+	headers.SetBytesV("Sec-WebSocket-Extensions", headers.Peek("Sec-Websocket-Extensions"))
+	headers.Del("Sec-Websocket-Extensions")
+
+	headers.SetBytesV("Sec-WebSocket-Accept", headers.Peek("Sec-Websocket-Accept"))
+	headers.Del("Sec-Websocket-Accept")
+
+	headers.SetBytesV("Sec-WebSocket-Protocol", headers.Peek("Sec-Websocket-Protocol"))
+	headers.Del("Sec-Websocket-Protocol")
+
+	headers.SetBytesV("Sec-WebSocket-Version", headers.Peek("Sec-Websocket-Version"))
+	headers.DelBytes([]byte("Sec-Websocket-Version"))
+}

pkg/proxy/fast/proxy_test.go

@@ -0,0 +1,311 @@
+package fast
+
+import (
+	"crypto/tls"
+	"crypto/x509"
+	"encoding/base64"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/http/httputil"
+	"net/url"
+	"testing"
+	"time"
+
+	"github.com/armon/go-socks5"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/config/static"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
+	"github.com/traefik/traefik/v3/pkg/tls/generate"
+)
+
+const (
+	proxyHTTP   = "http"
+	proxyHTTPS  = "https"
+	proxySocks5 = "socks"
+)
+
+type authCreds struct {
+	user     string
+	password string
+}
+
+func TestProxyFromEnvironment(t *testing.T) {
+	testCases := []struct {
+		desc      string
+		proxyType string
+		tls       bool
+		auth      *authCreds
+	}{
+		{
+			desc:      "Proxy HTTP with HTTP Backend",
+			proxyType: proxyHTTP,
+		},
+		{
+			desc:      "Proxy HTTP with HTTP backend and proxy auth",
+			proxyType: proxyHTTP,
+			tls:       false,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+		{
+			desc:      "Proxy HTTP with HTTPS backend",
+			proxyType: proxyHTTP,
+			tls:       true,
+		},
+		{
+			desc:      "Proxy HTTP with HTTPS backend and proxy auth",
+			proxyType: proxyHTTP,
+			tls:       true,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+		{
+			desc:      "Proxy HTTPS with HTTP backend",
+			proxyType: proxyHTTPS,
+		},
+		{
+			desc:      "Proxy HTTPS with HTTP backend and proxy auth",
+			proxyType: proxyHTTPS,
+			tls:       false,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+		{
+			desc:      "Proxy HTTPS with HTTPS backend",
+			proxyType: proxyHTTPS,
+			tls:       true,
+		},
+		{
+			desc:      "Proxy HTTPS with HTTPS backend and proxy auth",
+			proxyType: proxyHTTPS,
+			tls:       true,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+		{
+			desc:      "Proxy Socks5 with HTTP backend",
+			proxyType: proxySocks5,
+		},
+		{
+			desc:      "Proxy Socks5 with HTTP backend and proxy auth",
+			proxyType: proxySocks5,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+		{
+			desc:      "Proxy Socks5 with HTTPS backend",
+			proxyType: proxySocks5,
+			tls:       true,
+		},
+		{
+			desc:      "Proxy Socks5 with HTTPS backend and proxy auth",
+			proxyType: proxySocks5,
+			tls:       true,
+			auth: &authCreds{
+				user:     "user",
+				password: "password",
+			},
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			backendURL, backendCert := newBackendServer(t, test.tls, http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				_, _ = rw.Write([]byte("backend"))
+			}))
+
+			var proxyCalled bool
+			proxyHandler := http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+				proxyCalled = true
+
+				if test.auth != nil {
+					proxyAuth := "Basic " + base64.StdEncoding.EncodeToString([]byte(test.auth.user+":"+test.auth.password))
+					require.Equal(t, proxyAuth, req.Header.Get("Proxy-Authorization"))
+				}
+
+				if req.Method != http.MethodConnect {
+					proxy := httputil.NewSingleHostReverseProxy(testhelpers.MustParseURL("http://" + req.Host))
+					proxy.ServeHTTP(rw, req)
+					return
+				}
+
+				// CONNECT method
+				conn, err := net.Dial("tcp", req.Host)
+				require.NoError(t, err)
+
+				hj, ok := rw.(http.Hijacker)
+				require.True(t, ok)
+
+				rw.WriteHeader(http.StatusOK)
+				connHj, _, err := hj.Hijack()
+				require.NoError(t, err)
+
+				go func() { _, _ = io.Copy(connHj, conn) }()
+				_, _ = io.Copy(conn, connHj)
+			})
+
+			var proxyURL string
+			var proxyCert *x509.Certificate
+
+			switch test.proxyType {
+			case proxySocks5:
+				ln, err := net.Listen("tcp", ":0")
+				require.NoError(t, err)
+
+				proxyURL = fmt.Sprintf("socks5://%s", ln.Addr())
+
+				go func() {
+					conn, err := ln.Accept()
+					require.NoError(t, err)
+
+					proxyCalled = true
+
+					conf := &socks5.Config{}
+					if test.auth != nil {
+						conf.Credentials = socks5.StaticCredentials{test.auth.user: test.auth.password}
+					}
+
+					server, err := socks5.New(conf)
+					require.NoError(t, err)
+
+					// We are not checking the error, because ServeConn is blocked until the client or the backend
+					// connection is closed which, in some cases, raises a connection reset by peer error.
+					_ = server.ServeConn(conn)
+
+					err = ln.Close()
+					require.NoError(t, err)
+				}()
+
+			case proxyHTTP:
+				proxyServer := httptest.NewServer(proxyHandler)
+				t.Cleanup(proxyServer.Close)
+
+				proxyURL = proxyServer.URL
+
+			case proxyHTTPS:
+				proxyServer := httptest.NewServer(proxyHandler)
+				t.Cleanup(proxyServer.Close)
+
+				proxyURL = proxyServer.URL
+				proxyCert = proxyServer.Certificate()
+			}
+
+			certPool := x509.NewCertPool()
+			if proxyCert != nil {
+				certPool.AddCert(proxyCert)
+			}
+			if backendCert != nil {
+				cert, err := x509.ParseCertificate(backendCert.Certificate[0])
+				require.NoError(t, err)
+
+				certPool.AddCert(cert)
+			}
+
+			builder := NewProxyBuilder(&transportManagerMock{tlsConfig: &tls.Config{RootCAs: certPool}}, static.FastProxyConfig{})
+			builder.proxy = func(req *http.Request) (*url.URL, error) {
+				u, err := url.Parse(proxyURL)
+				if err != nil {
+					return nil, err
+				}
+
+				if test.auth != nil {
+					u.User = url.UserPassword(test.auth.user, test.auth.password)
+				}
+
+				return u, nil
+			}
+
+			reverseProxy, err := builder.Build("foo", testhelpers.MustParseURL(backendURL), false)
+			require.NoError(t, err)
+
+			reverseProxyServer := httptest.NewServer(reverseProxy)
+			t.Cleanup(reverseProxyServer.Close)
+
+			client := http.Client{Timeout: 5 * time.Second}
+
+			resp, err := client.Get(reverseProxyServer.URL)
+			require.NoError(t, err)
+
+			assert.Equal(t, http.StatusOK, resp.StatusCode)
+
+			body, err := io.ReadAll(resp.Body)
+			require.NoError(t, err)
+
+			assert.Equal(t, "backend", string(body))
+			assert.True(t, proxyCalled)
+		})
+	}
+}
+
+func newCertificate(t *testing.T, domain string) *tls.Certificate {
+	t.Helper()
+
+	certPEM, keyPEM, err := generate.KeyPair(domain, time.Time{})
+	require.NoError(t, err)
+
+	certificate, err := tls.X509KeyPair(certPEM, keyPEM)
+	require.NoError(t, err)
+
+	return &certificate
+}
+
+func newBackendServer(t *testing.T, isTLS bool, handler http.Handler) (string, *tls.Certificate) {
+	t.Helper()
+
+	var ln net.Listener
+	var err error
+	var cert *tls.Certificate
+
+	scheme := "http"
+	domain := "backend.localhost"
+	if isTLS {
+		scheme = "https"
+
+		cert = newCertificate(t, domain)
+
+		ln, err = tls.Listen("tcp", ":0", &tls.Config{Certificates: []tls.Certificate{*cert}})
+		require.NoError(t, err)
+	} else {
+		ln, err = net.Listen("tcp", ":0")
+		require.NoError(t, err)
+	}
+
+	srv := &http.Server{Handler: handler}
+	go func() { _ = srv.Serve(ln) }()
+
+	t.Cleanup(func() { _ = srv.Close() })
+
+	_, port, err := net.SplitHostPort(ln.Addr().String())
+	require.NoError(t, err)
+
+	backendURL := fmt.Sprintf("%s://%s:%s", scheme, domain, port)
+
+	return backendURL, cert
+}
+
+type transportManagerMock struct {
+	tlsConfig *tls.Config
+}
+
+func (r *transportManagerMock) GetTLSConfig(_ string) (*tls.Config, error) {
+	return r.tlsConfig, nil
+}
+
+func (r *transportManagerMock) Get(_ string) (*dynamic.ServersTransport, error) {
+	return &dynamic.ServersTransport{}, nil
+}

pkg/proxy/fast/proxy_websocket_test.go

@@ -0,0 +1,693 @@
+package fast
+
+import (
+	"bufio"
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"net"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+	"time"
+
+	gorillawebsocket "github.com/gorilla/websocket"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
+	"golang.org/x/net/websocket"
+)
+
+func TestWebSocketTCPClose(t *testing.T) {
+	errChan := make(chan error, 1)
+	upgrader := gorillawebsocket.Upgrader{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		c, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer c.Close()
+
+		for {
+			_, _, err := c.ReadMessage()
+			if err != nil {
+				errChan <- err
+				break
+			}
+		}
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+
+	proxyAddr := proxy.Listener.Addr().String()
+	_, conn, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+	).open()
+	require.NoError(t, err)
+
+	conn.Close()
+
+	serverErr := <-errChan
+
+	var wsErr *gorillawebsocket.CloseError
+	require.ErrorAs(t, serverErr, &wsErr)
+	assert.Equal(t, 1006, wsErr.Code)
+}
+
+func TestWebSocketPingPong(t *testing.T) {
+	upgrader := gorillawebsocket.Upgrader{
+		HandshakeTimeout: 10 * time.Second,
+		CheckOrigin: func(*http.Request) bool {
+			return true
+		},
+	}
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/ws", func(writer http.ResponseWriter, request *http.Request) {
+		ws, err := upgrader.Upgrade(writer, request, nil)
+		require.NoError(t, err)
+
+		ws.SetPingHandler(func(appData string) error {
+			err = ws.WriteMessage(gorillawebsocket.PongMessage, []byte(appData+"Pong"))
+			require.NoError(t, err)
+
+			return nil
+		})
+
+		_, _, _ = ws.ReadMessage()
+	})
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		mux.ServeHTTP(w, req)
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	serverAddr := proxy.Listener.Addr().String()
+
+	headers := http.Header{}
+	webSocketURL := "ws://" + serverAddr + "/ws"
+	headers.Add("Origin", webSocketURL)
+
+	conn, resp, err := gorillawebsocket.DefaultDialer.Dial(webSocketURL, headers)
+	require.NoError(t, err, "Error during Dial with response: %+v", resp)
+	defer conn.Close()
+
+	goodErr := fmt.Errorf("signal: %s", "Good data")
+	badErr := fmt.Errorf("signal: %s", "Bad data")
+	conn.SetPongHandler(func(data string) error {
+		if data == "PingPong" {
+			return goodErr
+		}
+
+		return badErr
+	})
+
+	err = conn.WriteControl(gorillawebsocket.PingMessage, []byte("Ping"), time.Now().Add(time.Second))
+	require.NoError(t, err)
+
+	_, _, err = conn.ReadMessage()
+
+	if !errors.Is(err, goodErr) {
+		require.NoError(t, err)
+	}
+}
+
+func TestWebSocketEcho(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.Handle("/ws", websocket.Handler(func(conn *websocket.Conn) {
+		msg := make([]byte, 4)
+
+		n, err := conn.Read(msg)
+		require.NoError(t, err)
+
+		_, err = conn.Write(msg[:n])
+		require.NoError(t, err)
+
+		err = conn.Close()
+		require.NoError(t, err)
+	}))
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		mux.ServeHTTP(w, req)
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	serverAddr := proxy.Listener.Addr().String()
+
+	headers := http.Header{}
+	webSocketURL := "ws://" + serverAddr + "/ws"
+	headers.Add("Origin", webSocketURL)
+
+	conn, resp, err := gorillawebsocket.DefaultDialer.Dial(webSocketURL, headers)
+	require.NoError(t, err, "Error during Dial with response: %+v", resp)
+
+	err = conn.WriteMessage(gorillawebsocket.TextMessage, []byte("OK"))
+	require.NoError(t, err)
+
+	_, msg, err := conn.ReadMessage()
+	require.NoError(t, err)
+
+	assert.Equal(t, "OK", string(msg))
+
+	err = conn.Close()
+	require.NoError(t, err)
+}
+
+func TestWebSocketPassHost(t *testing.T) {
+	testCases := []struct {
+		desc     string
+		passHost bool
+		expected string
+	}{
+		{
+			desc:     "PassHost false",
+			passHost: false,
+		},
+		{
+			desc:     "PassHost true",
+			passHost: true,
+			expected: "example.com",
+		},
+	}
+
+	for _, test := range testCases {
+		t.Run(test.desc, func(t *testing.T) {
+			mux := http.NewServeMux()
+			mux.Handle("/ws", websocket.Handler(func(conn *websocket.Conn) {
+				req := conn.Request()
+
+				if test.passHost {
+					require.Equal(t, test.expected, req.Host)
+				} else {
+					require.NotEqual(t, test.expected, req.Host)
+				}
+
+				msg := make([]byte, 4)
+
+				n, err := conn.Read(msg)
+				require.NoError(t, err)
+
+				_, err = conn.Write(msg[:n])
+				require.NoError(t, err)
+
+				err = conn.Close()
+				require.NoError(t, err)
+			}))
+
+			srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+				mux.ServeHTTP(w, req)
+			}))
+			defer srv.Close()
+
+			proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+
+			serverAddr := proxy.Listener.Addr().String()
+
+			headers := http.Header{}
+			webSocketURL := "ws://" + serverAddr + "/ws"
+			headers.Add("Origin", webSocketURL)
+			headers.Add("Host", "example.com")
+
+			conn, resp, err := gorillawebsocket.DefaultDialer.Dial(webSocketURL, headers)
+			require.NoError(t, err, "Error during Dial with response: %+v", resp)
+
+			err = conn.WriteMessage(gorillawebsocket.TextMessage, []byte("OK"))
+			require.NoError(t, err)
+
+			_, msg, err := conn.ReadMessage()
+			require.NoError(t, err)
+
+			assert.Equal(t, "OK", string(msg))
+
+			err = conn.Close()
+			require.NoError(t, err)
+		})
+	}
+}
+
+func TestWebSocketServerWithoutCheckOrigin(t *testing.T) {
+	upgrader := gorillawebsocket.Upgrader{CheckOrigin: func(r *http.Request) bool {
+		return true
+	}}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		c, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer c.Close()
+		for {
+			mt, message, err := c.ReadMessage()
+			if err != nil {
+				break
+			}
+			err = c.WriteMessage(mt, message)
+			if err != nil {
+				break
+			}
+		}
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("ok"),
+		withOrigin("http://127.0.0.2"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+func TestWebSocketRequestWithOrigin(t *testing.T) {
+	upgrader := gorillawebsocket.Upgrader{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		c, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer c.Close()
+		for {
+			mt, message, err := c.ReadMessage()
+			if err != nil {
+				break
+			}
+			err = c.WriteMessage(mt, message)
+			if err != nil {
+				break
+			}
+		}
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+	_, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("echo"),
+		withOrigin("http://127.0.0.2"),
+	).send()
+	require.EqualError(t, err, "bad status")
+
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("ok"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+func TestWebSocketRequestWithQueryParams(t *testing.T) {
+	upgrader := gorillawebsocket.Upgrader{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+
+		assert.Equal(t, "test", r.URL.Query().Get("query"))
+		for {
+			mt, message, err := conn.ReadMessage()
+			if err != nil {
+				break
+			}
+
+			err = conn.WriteMessage(mt, message)
+			if err != nil {
+				break
+			}
+		}
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws?query=test"),
+		withData("ok"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+func TestWebSocketRequestWithHeadersInResponseWriter(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.Handle("/ws", websocket.Handler(func(conn *websocket.Conn) {
+		_ = conn.Close()
+	}))
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		mux.ServeHTTP(w, req)
+	}))
+	defer srv.Close()
+
+	u := parseURI(t, srv.URL)
+
+	f, err := NewReverseProxy(u, nil, true, false, 0, newConnPool(1, 0, func() (net.Conn, error) {
+		return net.Dial("tcp", u.Host)
+	}))
+	require.NoError(t, err)
+
+	proxy := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		req.URL = parseURI(t, srv.URL)
+		w.Header().Set("HEADER-KEY", "HEADER-VALUE")
+		f.ServeHTTP(w, req)
+	}))
+	defer proxy.Close()
+
+	serverAddr := proxy.Listener.Addr().String()
+
+	headers := http.Header{}
+	webSocketURL := "ws://" + serverAddr + "/ws"
+	headers.Add("Origin", webSocketURL)
+	conn, resp, err := gorillawebsocket.DefaultDialer.Dial(webSocketURL, headers)
+	require.NoError(t, err, "Error during Dial with response: %+v", err, resp)
+	defer conn.Close()
+
+	assert.Equal(t, "HEADER-VALUE", resp.Header.Get("HEADER-KEY"))
+}
+
+func TestWebSocketRequestWithEncodedChar(t *testing.T) {
+	upgrader := gorillawebsocket.Upgrader{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+		assert.Equal(t, "/%3A%2F%2F", r.URL.EscapedPath())
+		for {
+			mt, message, err := conn.ReadMessage()
+			if err != nil {
+				break
+			}
+			err = conn.WriteMessage(mt, message)
+			if err != nil {
+				break
+			}
+		}
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/%3A%2F%2F"),
+		withData("ok"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+func TestWebSocketUpgradeFailed(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.HandleFunc("/ws", func(w http.ResponseWriter, req *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+	})
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		mux.ServeHTTP(w, req)
+	}))
+	defer srv.Close()
+
+	u := parseURI(t, srv.URL)
+	f, err := NewReverseProxy(u, nil, true, false, 0, newConnPool(1, 0, func() (net.Conn, error) {
+		return net.Dial("tcp", u.Host)
+	}))
+	require.NoError(t, err)
+
+	proxy := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		path := req.URL.Path // keep the original path
+
+		if path != "/ws" {
+			w.WriteHeader(http.StatusOK)
+			return
+		}
+
+		// Set new backend URL
+		req.URL = parseURI(t, srv.URL)
+		req.URL.Path = path
+		f.ServeHTTP(w, req)
+	}))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+	conn, err := net.DialTimeout("tcp", proxyAddr, dialTimeout)
+
+	require.NoError(t, err)
+	defer conn.Close()
+
+	req, err := http.NewRequest(http.MethodGet, "ws://127.0.0.1/ws", nil)
+	require.NoError(t, err)
+
+	req.Header.Add("upgrade", "websocket")
+	req.Header.Add("Connection", "upgrade")
+
+	err = req.Write(conn)
+	require.NoError(t, err)
+
+	// First request works with 400
+	br := bufio.NewReader(conn)
+	resp, err := http.ReadResponse(br, req)
+	require.NoError(t, err)
+
+	assert.Equal(t, 400, resp.StatusCode)
+}
+
+func TestForwardsWebsocketTraffic(t *testing.T) {
+	mux := http.NewServeMux()
+	mux.Handle("/ws", websocket.Handler(func(conn *websocket.Conn) {
+		_, err := conn.Write([]byte("ok"))
+		require.NoError(t, err)
+
+		err = conn.Close()
+		require.NoError(t, err)
+	}))
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		mux.ServeHTTP(w, req)
+	}))
+	defer srv.Close()
+
+	proxy := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxy.Close()
+
+	proxyAddr := proxy.Listener.Addr().String()
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("echo"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+func createTLSWebsocketServer() *httptest.Server {
+	upgrader := gorillawebsocket.Upgrader{}
+	srv := httptest.NewTLSServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			return
+		}
+		defer conn.Close()
+		for {
+			mt, message, err := conn.ReadMessage()
+			if err != nil {
+				break
+			}
+
+			err = conn.WriteMessage(mt, message)
+			if err != nil {
+				break
+			}
+		}
+	}))
+	return srv
+}
+
+func TestWebSocketTransferTLSConfig(t *testing.T) {
+	srv := createTLSWebsocketServer()
+	defer srv.Close()
+
+	proxyWithoutTLSConfig := createProxyWithForwarder(t, srv.URL, createConnectionPool(srv.URL, nil))
+	defer proxyWithoutTLSConfig.Close()
+
+	proxyAddr := proxyWithoutTLSConfig.Listener.Addr().String()
+
+	_, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("ok"),
+	).send()
+
+	require.EqualError(t, err, "bad status")
+
+	pool := createConnectionPool(srv.URL, &tls.Config{InsecureSkipVerify: true})
+
+	proxyWithTLSConfig := createProxyWithForwarder(t, srv.URL, pool)
+	defer proxyWithTLSConfig.Close()
+
+	proxyAddr = proxyWithTLSConfig.Listener.Addr().String()
+
+	resp, err := newWebsocketRequest(
+		withServer(proxyAddr),
+		withPath("/ws"),
+		withData("ok"),
+	).send()
+
+	require.NoError(t, err)
+	assert.Equal(t, "ok", resp)
+}
+
+const dialTimeout = time.Second
+
+type websocketRequestOpt func(w *websocketRequest)
+
+func withServer(server string) websocketRequestOpt {
+	return func(w *websocketRequest) {
+		w.ServerAddr = server
+	}
+}
+
+func withPath(path string) websocketRequestOpt {
+	return func(w *websocketRequest) {
+		w.Path = path
+	}
+}
+
+func withData(data string) websocketRequestOpt {
+	return func(w *websocketRequest) {
+		w.Data = data
+	}
+}
+
+func withOrigin(origin string) websocketRequestOpt {
+	return func(w *websocketRequest) {
+		w.Origin = origin
+	}
+}
+
+func newWebsocketRequest(opts ...websocketRequestOpt) *websocketRequest {
+	wsrequest := &websocketRequest{}
+	for _, opt := range opts {
+		opt(wsrequest)
+	}
+
+	if wsrequest.Origin == "" {
+		wsrequest.Origin = "http://" + wsrequest.ServerAddr
+	}
+
+	if wsrequest.Config == nil {
+		wsrequest.Config, _ = websocket.NewConfig(fmt.Sprintf("ws://%s%s", wsrequest.ServerAddr, wsrequest.Path), wsrequest.Origin)
+	}
+
+	return wsrequest
+}
+
+type websocketRequest struct {
+	ServerAddr string
+	Path       string
+	Data       string
+	Origin     string
+	Config     *websocket.Config
+}
+
+func (w *websocketRequest) send() (string, error) {
+	conn, _, err := w.open()
+	if err != nil {
+		return "", err
+	}
+	defer conn.Close()
+
+	if _, err := conn.Write([]byte(w.Data)); err != nil {
+		return "", err
+	}
+
+	msg := make([]byte, 512)
+
+	var n int
+	n, err = conn.Read(msg)
+	if err != nil {
+		return "", err
+	}
+
+	received := string(msg[:n])
+	return received, nil
+}
+
+func (w *websocketRequest) open() (*websocket.Conn, net.Conn, error) {
+	client, err := net.DialTimeout("tcp", w.ServerAddr, dialTimeout)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	conn, err := websocket.NewClient(w.Config, client)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	return conn, client, err
+}
+
+func parseURI(t *testing.T, uri string) *url.URL {
+	t.Helper()
+
+	out, err := url.ParseRequestURI(uri)
+	require.NoError(t, err)
+
+	return out
+}
+
+func createConnectionPool(target string, tlsConfig *tls.Config) *connPool {
+	u := testhelpers.MustParseURL(target)
+	return newConnPool(200, 0, func() (net.Conn, error) {
+		if tlsConfig != nil {
+			return tls.Dial("tcp", u.Host, tlsConfig)
+		}
+
+		return net.Dial("tcp", u.Host)
+	})
+}
+
+func createProxyWithForwarder(t *testing.T, uri string, pool *connPool) *httptest.Server {
+	t.Helper()
+
+	u := parseURI(t, uri)
+	proxy, err := NewReverseProxy(u, nil, false, true, 0, pool)
+	require.NoError(t, err)
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		path := req.URL.Path // keep the original path
+		// Set new backend URL
+		req.URL = u
+		req.URL.Path = path
+
+		proxy.ServeHTTP(w, req)
+	}))
+	t.Cleanup(srv.Close)
+
+	return srv
+}

pkg/proxy/fast/upgrade.go

@@ -0,0 +1,104 @@
+package fast
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"strings"
+
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
+	"github.com/valyala/fasthttp"
+	"golang.org/x/net/http/httpguts"
+)
+
+// switchProtocolCopier exists so goroutines proxying data back and
+// forth have nice names in stacks.
+type switchProtocolCopier struct {
+	user, backend io.ReadWriter
+}
+
+func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
+	_, err := io.Copy(c.user, c.backend)
+	errc <- err
+}
+
+func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
+	_, err := io.Copy(c.backend, c.user)
+	errc <- err
+}
+
+func handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, reqUpType string, res *fasthttp.Response, backConn net.Conn) {
+	defer backConn.Close()
+
+	resUpType := upgradeTypeFastHTTP(&res.Header)
+
+	if !strings.EqualFold(reqUpType, resUpType) {
+		httputil.ErrorHandler(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
+		return
+	}
+
+	hj, ok := rw.(http.Hijacker)
+	if !ok {
+		httputil.ErrorHandler(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
+		return
+	}
+	backConnCloseCh := make(chan bool)
+	go func() {
+		// Ensure that the cancellation of a request closes the backend.
+		// See issue https://golang.org/issue/35559.
+		select {
+		case <-req.Context().Done():
+		case <-backConnCloseCh:
+		}
+		_ = backConn.Close()
+	}()
+
+	defer close(backConnCloseCh)
+
+	conn, brw, err := hj.Hijack()
+	if err != nil {
+		httputil.ErrorHandler(rw, req, fmt.Errorf("hijack failed on protocol switch: %w", err))
+		return
+	}
+	defer conn.Close()
+
+	for k, values := range rw.Header() {
+		for _, v := range values {
+			res.Header.Add(k, v)
+		}
+	}
+
+	if err := res.Header.Write(brw.Writer); err != nil {
+		httputil.ErrorHandler(rw, req, fmt.Errorf("response write: %w", err))
+		return
+	}
+
+	if err := brw.Flush(); err != nil {
+		httputil.ErrorHandler(rw, req, fmt.Errorf("response flush: %w", err))
+		return
+	}
+
+	errc := make(chan error, 1)
+	spc := switchProtocolCopier{user: conn, backend: backConn}
+	go spc.copyToBackend(errc)
+	go spc.copyFromBackend(errc)
+	<-errc
+}
+
+func upgradeType(h http.Header) string {
+	if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
+		return ""
+	}
+
+	return h.Get("Upgrade")
+}
+
+func upgradeTypeFastHTTP(h fasthttpHeader) string {
+	if !bytes.Contains(h.Peek("Connection"), []byte("Upgrade")) {
+		return ""
+	}
+
+	return string(h.Peek("Upgrade"))
+}

pkg/proxy/httputil/bufferpool.go

@@ -1,23 +1,25 @@
-package service
+package httputil
 
 import "sync"
 
-const bufferPoolSize = 32 * 1024
+const bufferSize = 32 * 1024
-
-func newBufferPool() *bufferPool {
-	return &bufferPool{
-		pool: sync.Pool{
-			New: func() interface{} {
-				return make([]byte, bufferPoolSize)
-			},
-		},
-	}
-}
 
 type bufferPool struct {
 	pool sync.Pool
 }
 
+func newBufferPool() *bufferPool {
+	b := &bufferPool{
+		pool: sync.Pool{},
+	}
+
+	b.pool.New = func() interface{} {
+		return make([]byte, bufferSize)
+	}
+
+	return b
+}
+
 func (b *bufferPool) Get() []byte {
 	return b.pool.Get().([]byte)
 }

pkg/proxy/httputil/builder.go

@@ -0,0 +1,54 @@
+package httputil
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/metrics"
+)
+
+// TransportManager manages transport used for backend communications.
+type TransportManager interface {
+	Get(name string) (*dynamic.ServersTransport, error)
+	GetRoundTripper(name string) (http.RoundTripper, error)
+	GetTLSConfig(name string) (*tls.Config, error)
+}
+
+// ProxyBuilder handles the http.RoundTripper for httputil reverse proxies.
+type ProxyBuilder struct {
+	bufferPool             *bufferPool
+	transportManager       TransportManager
+	semConvMetricsRegistry *metrics.SemConvMetricsRegistry
+}
+
+// NewProxyBuilder creates a new ProxyBuilder.
+func NewProxyBuilder(transportManager TransportManager, semConvMetricsRegistry *metrics.SemConvMetricsRegistry) *ProxyBuilder {
+	return &ProxyBuilder{
+		bufferPool:             newBufferPool(),
+		transportManager:       transportManager,
+		semConvMetricsRegistry: semConvMetricsRegistry,
+	}
+}
+
+// Update does nothing.
+func (r *ProxyBuilder) Update(_ map[string]*dynamic.ServersTransport) {}
+
+// Build builds a new httputil.ReverseProxy with the given configuration.
+func (r *ProxyBuilder) Build(cfgName string, targetURL *url.URL, shouldObserve, passHostHeader bool, flushInterval time.Duration) (http.Handler, error) {
+	roundTripper, err := r.transportManager.GetRoundTripper(cfgName)
+	if err != nil {
+		return nil, fmt.Errorf("getting RoundTripper: %w", err)
+	}
+
+	if shouldObserve {
+		// Wrapping the roundTripper with the Tracing roundTripper,
+		// to handle the reverseProxy client span creation.
+		roundTripper = newObservabilityRoundTripper(r.semConvMetricsRegistry, roundTripper)
+	}
+
+	return buildSingleHostProxy(targetURL, passHostHeader, flushInterval, roundTripper, r.bufferPool), nil
+}

pkg/proxy/httputil/builder_test.go

@@ -0,0 +1,56 @@
+package httputil
+
+import (
+	"crypto/tls"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
+)
+
+func TestEscapedPath(t *testing.T) {
+	var gotEscapedPath string
+	srv := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		gotEscapedPath = req.URL.EscapedPath()
+	}))
+
+	transportManager := &transportManagerMock{
+		roundTrippers: map[string]http.RoundTripper{"default": &http.Transport{}},
+	}
+
+	p, err := NewProxyBuilder(transportManager, nil).Build("default", testhelpers.MustParseURL(srv.URL), false, true, 0)
+	require.NoError(t, err)
+
+	proxy := httptest.NewServer(http.HandlerFunc(p.ServeHTTP))
+
+	_, err = http.Get(proxy.URL + "/%3A%2F%2F")
+	require.NoError(t, err)
+
+	assert.Equal(t, "/%3A%2F%2F", gotEscapedPath)
+}
+
+type transportManagerMock struct {
+	roundTrippers map[string]http.RoundTripper
+}
+
+func (t *transportManagerMock) GetRoundTripper(name string) (http.RoundTripper, error) {
+	roundTripper, ok := t.roundTrippers[name]
+	if !ok {
+		return nil, errors.New("no transport for " + name)
+	}
+
+	return roundTripper, nil
+}
+
+func (t *transportManagerMock) GetTLSConfig(_ string) (*tls.Config, error) {
+	panic("implement me")
+}
+
+func (t *transportManagerMock) Get(_ string) (*dynamic.ServersTransport, error) {
+	panic("implement me")
+}

pkg/proxy/httputil/observability.go

@@ -1,4 +1,4 @@
-package service
+package httputil
 
 import (
 	"context"
@@ -23,6 +23,13 @@ type wrapper struct {
 	rt                    http.RoundTripper
 }
 
+func newObservabilityRoundTripper(semConvMetricRegistry *metrics.SemConvMetricsRegistry, rt http.RoundTripper) http.RoundTripper {
+	return &wrapper{
+		semConvMetricRegistry: semConvMetricRegistry,
+		rt:                    rt,
+	}
+}
+
 func (t *wrapper) RoundTrip(req *http.Request) (*http.Response, error) {
 	start := time.Now()
 	var span trace.Span
@@ -42,7 +49,7 @@ func (t *wrapper) RoundTrip(req *http.Request) (*http.Response, error) {
 	var headers http.Header
 	response, err := t.rt.RoundTrip(req)
 	if err != nil {
-		statusCode = computeStatusCode(err)
+		statusCode = ComputeStatusCode(err)
 	}
 	if response != nil {
 		statusCode = response.StatusCode
@@ -96,10 +103,3 @@ func (t *wrapper) RoundTrip(req *http.Request) (*http.Response, error) {
 
 	return response, err
 }
-
-func newObservabilityRoundTripper(semConvMetricRegistry *metrics.SemConvMetricsRegistry, rt http.RoundTripper) http.RoundTripper {
-	return &wrapper{
-		semConvMetricRegistry: semConvMetricRegistry,
-		rt:                    rt,
-	}
-}

pkg/proxy/httputil/observability_test.go

@@ -1,4 +1,4 @@
-package service
+package httputil
 
 import (
 	"context"

pkg/proxy/httputil/proxy.go

@@ -1,4 +1,4 @@
-package service
+package httputil
 
 import (
 	"context"
@@ -27,7 +27,7 @@ func buildSingleHostProxy(target *url.URL, passHostHeader bool, flushInterval ti
 		Transport:     roundTripper,
 		FlushInterval: flushInterval,
 		BufferPool:    bufferPool,
-		ErrorHandler:  errorHandler,
+		ErrorHandler:  ErrorHandler,
 	}
 }
 
@@ -93,8 +93,9 @@ func isWebSocketUpgrade(req *http.Request) bool {
 		strings.EqualFold(req.Header.Get("Upgrade"), "websocket")
 }
 
-func errorHandler(w http.ResponseWriter, req *http.Request, err error) {
+// ErrorHandler is the http.Handler called when something goes wrong when forwarding the request.
-	statusCode := computeStatusCode(err)
+func ErrorHandler(w http.ResponseWriter, req *http.Request, err error) {
+	statusCode := ComputeStatusCode(err)
 
 	logger := log.Ctx(req.Context())
 	logger.Debug().Err(err).Msgf("%d %s", statusCode, statusText(statusCode))
@@ -105,7 +106,8 @@ func errorHandler(w http.ResponseWriter, req *http.Request, err error) {
 	}
 }
 
-func computeStatusCode(err error) int {
+// ComputeStatusCode computes the HTTP status code according to the given error.
+func ComputeStatusCode(err error) int {
 	switch {
 	case errors.Is(err, io.EOF):
 		return http.StatusBadGateway

pkg/proxy/httputil/proxy_websocket_test.go

@@ -1,4 +1,4 @@
-package service
+package httputil
 
 import (
 	"bufio"
@@ -8,13 +8,13 @@ import (
 	"net"
 	"net/http"
 	"net/http/httptest"
-	"net/url"
 	"testing"
 	"time"
 
 	gorillawebsocket "github.com/gorilla/websocket"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
 	"golang.org/x/net/websocket"
 )
 
@@ -27,6 +27,7 @@ func TestWebSocketTCPClose(t *testing.T) {
 			return
 		}
 		defer c.Close()
+
 		for {
 			_, _, err := c.ReadMessage()
 			if err != nil {
@@ -71,6 +72,7 @@ func TestWebSocketPingPong(t *testing.T) {
 		ws.SetPingHandler(func(appData string) error {
 			err = ws.WriteMessage(gorillawebsocket.PongMessage, []byte(appData+"Pong"))
 			require.NoError(t, err)
+
 			return nil
 		})
 
@@ -97,6 +99,7 @@ func TestWebSocketPingPong(t *testing.T) {
 		if data == "PingPong" {
 			return goodErr
 		}
+
 		return badErr
 	})
 
@@ -104,7 +107,6 @@ func TestWebSocketPingPong(t *testing.T) {
 	require.NoError(t, err)
 
 	_, _, err = conn.ReadMessage()
-
 	if !errors.Is(err, goodErr) {
 		require.NoError(t, err)
 	}
@@ -114,12 +116,10 @@ func TestWebSocketEcho(t *testing.T) {
 	mux := http.NewServeMux()
 	mux.Handle("/ws", websocket.Handler(func(conn *websocket.Conn) {
 		msg := make([]byte, 4)
-		_, err := conn.Read(msg)
+		n, err := conn.Read(msg)
 		require.NoError(t, err)
 
-		fmt.Println(string(msg))
+		_, err = conn.Write(msg[:n])
-
-		_, err = conn.Write(msg)
 		require.NoError(t, err)
 
 		err = conn.Close()
@@ -142,7 +142,10 @@ func TestWebSocketEcho(t *testing.T) {
 	err = conn.WriteMessage(gorillawebsocket.TextMessage, []byte("OK"))
 	require.NoError(t, err)
 
-	fmt.Println(conn.ReadMessage())
+	_, msg, err := conn.ReadMessage()
+	require.NoError(t, err)
+
+	assert.Equal(t, "OK", string(msg))
 
 	err = conn.Close()
 	require.NoError(t, err)
@@ -178,11 +181,10 @@ func TestWebSocketPassHost(t *testing.T) {
 				}
 
 				msg := make([]byte, 4)
-				_, err := conn.Read(msg)
+				n, err := conn.Read(msg)
 				require.NoError(t, err)
 
-				fmt.Println(string(msg))
+				_, err = conn.Write(msg[:n])
-				_, err = conn.Write(msg)
 				require.NoError(t, err)
 
 				err = conn.Close()
@@ -207,7 +209,10 @@ func TestWebSocketPassHost(t *testing.T) {
 			err = conn.WriteMessage(gorillawebsocket.TextMessage, []byte("OK"))
 			require.NoError(t, err)
 
-			fmt.Println(conn.ReadMessage())
+			_, msg, err := conn.ReadMessage()
+			require.NoError(t, err)
+
+			assert.Equal(t, "OK", string(msg))
 
 			err = conn.Close()
 			require.NoError(t, err)
@@ -216,27 +221,8 @@ func TestWebSocketPassHost(t *testing.T) {
 }
 
 func TestWebSocketServerWithoutCheckOrigin(t *testing.T) {
-	upgrader := gorillawebsocket.Upgrader{CheckOrigin: func(r *http.Request) bool {
+	upgrader := gorillawebsocket.Upgrader{CheckOrigin: func(*http.Request) bool { return true }}
-		return true
+	srv := createServer(t, upgrader, func(*http.Request) {})
-	}}
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		c, err := upgrader.Upgrade(w, r, nil)
-		if err != nil {
-			return
-		}
-		defer c.Close()
-		for {
-			mt, message, err := c.ReadMessage()
-			if err != nil {
-				break
-			}
-			err = c.WriteMessage(mt, message)
-			if err != nil {
-				break
-			}
-		}
-	}))
-	defer srv.Close()
 
 	proxy := createProxyWithForwarder(t, srv.URL, http.DefaultTransport)
 	defer proxy.Close()
@@ -254,25 +240,7 @@ func TestWebSocketServerWithoutCheckOrigin(t *testing.T) {
 }
 
 func TestWebSocketRequestWithOrigin(t *testing.T) {
-	upgrader := gorillawebsocket.Upgrader{}
+	srv := createServer(t, gorillawebsocket.Upgrader{}, func(*http.Request) {})
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		c, err := upgrader.Upgrade(w, r, nil)
-		if err != nil {
-			return
-		}
-		defer c.Close()
-		for {
-			mt, message, err := c.ReadMessage()
-			if err != nil {
-				break
-			}
-			err = c.WriteMessage(mt, message)
-			if err != nil {
-				break
-			}
-		}
-	}))
-	defer srv.Close()
 
 	proxy := createProxyWithForwarder(t, srv.URL, http.DefaultTransport)
 	defer proxy.Close()
@@ -297,26 +265,9 @@ func TestWebSocketRequestWithOrigin(t *testing.T) {
 }
 
 func TestWebSocketRequestWithQueryParams(t *testing.T) {
-	upgrader := gorillawebsocket.Upgrader{}
+	srv := createServer(t, gorillawebsocket.Upgrader{}, func(r *http.Request) {
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		conn, err := upgrader.Upgrade(w, r, nil)
-		if err != nil {
-			return
-		}
-		defer conn.Close()
 		assert.Equal(t, "test", r.URL.Query().Get("query"))
-		for {
+	})
-			mt, message, err := conn.ReadMessage()
-			if err != nil {
-				break
-			}
-			err = conn.WriteMessage(mt, message)
-			if err != nil {
-				break
-			}
-		}
-	}))
-	defer srv.Close()
 
 	proxy := createProxyWithForwarder(t, srv.URL, http.DefaultTransport)
 	defer proxy.Close()
@@ -341,11 +292,19 @@ func TestWebSocketRequestWithHeadersInResponseWriter(t *testing.T) {
 	srv := httptest.NewServer(mux)
 	defer srv.Close()
 
-	f := buildSingleHostProxy(parseURI(t, srv.URL), true, 0, http.DefaultTransport, nil)
+	transportManager := &transportManagerMock{
+		roundTrippers: map[string]http.RoundTripper{
+			"default@internal": &http.Transport{},
+		},
+	}
+
+	p, err := NewProxyBuilder(transportManager, nil).Build("default@internal", testhelpers.MustParseURL(srv.URL), false, true, 0)
+	require.NoError(t, err)
+
 	proxy := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-		req.URL = parseURI(t, srv.URL)
+		req.URL = testhelpers.MustParseURL(srv.URL)
 		w.Header().Set("HEADER-KEY", "HEADER-VALUE")
-		f.ServeHTTP(w, req)
+		p.ServeHTTP(w, req)
 	}))
 	defer proxy.Close()
 
@@ -363,26 +322,9 @@ func TestWebSocketRequestWithHeadersInResponseWriter(t *testing.T) {
 }
 
 func TestWebSocketRequestWithEncodedChar(t *testing.T) {
-	upgrader := gorillawebsocket.Upgrader{}
+	srv := createServer(t, gorillawebsocket.Upgrader{}, func(r *http.Request) {
-	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		conn, err := upgrader.Upgrade(w, r, nil)
-		if err != nil {
-			return
-		}
-		defer conn.Close()
 		assert.Equal(t, "/%3A%2F%2F", r.URL.EscapedPath())
-		for {
+	})
-			mt, message, err := conn.ReadMessage()
-			if err != nil {
-				break
-			}
-			err = conn.WriteMessage(mt, message)
-			if err != nil {
-				break
-			}
-		}
-	}))
-	defer srv.Close()
 
 	proxy := createProxyWithForwarder(t, srv.URL, http.DefaultTransport)
 	defer proxy.Close()
@@ -407,15 +349,23 @@ func TestWebSocketUpgradeFailed(t *testing.T) {
 	srv := httptest.NewServer(mux)
 	defer srv.Close()
 
-	f := buildSingleHostProxy(parseURI(t, srv.URL), true, 0, http.DefaultTransport, nil)
+	transportManager := &transportManagerMock{
+		roundTrippers: map[string]http.RoundTripper{
+			"default@internal": &http.Transport{},
+		},
+	}
+
+	p, err := NewProxyBuilder(transportManager, nil).Build("default@internal", testhelpers.MustParseURL(srv.URL), false, true, 0)
+	require.NoError(t, err)
+
 	proxy := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
 		path := req.URL.Path // keep the original path
 
 		if path == "/ws" {
 			// Set new backend URL
-			req.URL = parseURI(t, srv.URL)
+			req.URL = testhelpers.MustParseURL(srv.URL)
 			req.URL.Path = path
-			f.ServeHTTP(w, req)
+			p.ServeHTTP(w, req)
 		} else {
 			w.WriteHeader(http.StatusOK)
 		}
@@ -629,27 +579,60 @@ func (w *websocketRequest) open() (*websocket.Conn, net.Conn, error) {
 	return conn, client, err
 }
 
-func parseURI(t *testing.T, uri string) *url.URL {
-	t.Helper()
-
-	out, err := url.ParseRequestURI(uri)
-	require.NoError(t, err)
-	return out
-}
-
 func createProxyWithForwarder(t *testing.T, uri string, transport http.RoundTripper) *httptest.Server {
 	t.Helper()
 
-	u := parseURI(t, uri)
+	u := testhelpers.MustParseURL(uri)
-	proxy := buildSingleHostProxy(u, true, 0, transport, nil)
+
+	transportManager := &transportManagerMock{
+		roundTrippers: map[string]http.RoundTripper{"fwd": transport},
+	}
+
+	p, err := NewProxyBuilder(transportManager, nil).Build("fwd", u, false, true, 0)
+	require.NoError(t, err)
+
 	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
-		path := req.URL.Path // keep the original path
+		// keep the original path
+		path := req.URL.Path
+
 		// Set new backend URL
 		req.URL = u
 		req.URL.Path = path
 
-		proxy.ServeHTTP(w, req)
+		p.ServeHTTP(w, req)
 	}))
 	t.Cleanup(srv.Close)
+
+	return srv
+}
+
+func createServer(t *testing.T, upgrader gorillawebsocket.Upgrader, check func(*http.Request)) *httptest.Server {
+	t.Helper()
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		conn, err := upgrader.Upgrade(w, r, nil)
+		if err != nil {
+			t.Logf("Error during upgrade: %v", err)
+			return
+		}
+		defer conn.Close()
+
+		check(r)
+		for {
+			mt, message, err := conn.ReadMessage()
+			if err != nil {
+				t.Logf("Error during read: %v", err)
+				break
+			}
+
+			err = conn.WriteMessage(mt, message)
+			if err != nil {
+				t.Logf("Error during write: %v", err)
+				break
+			}
+		}
+	}))
+	t.Cleanup(srv.Close)
+
 	return srv
 }

pkg/proxy/smart_builder.go

@@ -0,0 +1,61 @@
+package proxy
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net/http"
+	"net/url"
+	"time"
+
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/config/static"
+	"github.com/traefik/traefik/v3/pkg/proxy/fast"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
+	"github.com/traefik/traefik/v3/pkg/server/service"
+)
+
+// TransportManager manages transport used for backend communications.
+type TransportManager interface {
+	Get(name string) (*dynamic.ServersTransport, error)
+	GetRoundTripper(name string) (http.RoundTripper, error)
+	GetTLSConfig(name string) (*tls.Config, error)
+}
+
+// SmartBuilder is a proxy builder which returns a fast proxy or httputil proxy corresponding
+// to the ServersTransport configuration.
+type SmartBuilder struct {
+	fastProxyBuilder *fast.ProxyBuilder
+	proxyBuilder     service.ProxyBuilder
+
+	transportManager httputil.TransportManager
+}
+
+// NewSmartBuilder creates and returns a new SmartBuilder instance.
+func NewSmartBuilder(transportManager TransportManager, proxyBuilder service.ProxyBuilder, fastProxyConfig static.FastProxyConfig) *SmartBuilder {
+	return &SmartBuilder{
+		fastProxyBuilder: fast.NewProxyBuilder(transportManager, fastProxyConfig),
+		proxyBuilder:     proxyBuilder,
+		transportManager: transportManager,
+	}
+}
+
+// Update is the handler called when the dynamic configuration is updated.
+func (b *SmartBuilder) Update(newConfigs map[string]*dynamic.ServersTransport) {
+	b.fastProxyBuilder.Update(newConfigs)
+}
+
+// Build builds an HTTP proxy for the given URL using the ServersTransport with the given name.
+func (b *SmartBuilder) Build(configName string, targetURL *url.URL, shouldObserve, passHostHeader bool, flushInterval time.Duration) (http.Handler, error) {
+	serversTransport, err := b.transportManager.Get(configName)
+	if err != nil {
+		return nil, fmt.Errorf("getting ServersTransport: %w", err)
+	}
+
+	// The fast proxy implementation cannot handle HTTP/2 requests for now.
+	// For the https scheme we cannot guess if the backend communication will use HTTP2,
+	// thus we check if HTTP/2 is disabled to use the fast proxy implementation when this is possible.
+	if targetURL.Scheme == "h2c" || (targetURL.Scheme == "https" && !serversTransport.DisableHTTP2) {
+		return b.proxyBuilder.Build(configName, targetURL, shouldObserve, passHostHeader, flushInterval)
+	}
+	return b.fastProxyBuilder.Build(configName, targetURL, passHostHeader)
+}

pkg/proxy/smart_builder_test.go

@@ -0,0 +1,113 @@
+package proxy
+
+import (
+	"encoding/pem"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	"github.com/traefik/traefik/v3/pkg/config/static"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
+	"github.com/traefik/traefik/v3/pkg/server/service"
+	"github.com/traefik/traefik/v3/pkg/testhelpers"
+	"github.com/traefik/traefik/v3/pkg/types"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
+)
+
+func TestSmartBuilder_Build(t *testing.T) {
+	tests := []struct {
+		desc             string
+		serversTransport dynamic.ServersTransport
+		fastProxyConfig  static.FastProxyConfig
+		https            bool
+		h2c              bool
+		wantFastProxy    bool
+	}{
+		{
+			desc:            "fastproxy",
+			fastProxyConfig: static.FastProxyConfig{Debug: true},
+			wantFastProxy:   true,
+		},
+		{
+			desc:            "fastproxy with https and without DisableHTTP2",
+			https:           true,
+			fastProxyConfig: static.FastProxyConfig{Debug: true},
+			wantFastProxy:   false,
+		},
+		{
+			desc:             "fastproxy with https and DisableHTTP2",
+			https:            true,
+			serversTransport: dynamic.ServersTransport{DisableHTTP2: true},
+			fastProxyConfig:  static.FastProxyConfig{Debug: true},
+			wantFastProxy:    true,
+		},
+		{
+			desc:            "fastproxy with h2c",
+			h2c:             true,
+			fastProxyConfig: static.FastProxyConfig{Debug: true},
+			wantFastProxy:   false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			var callCount int
+			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				callCount++
+				if test.wantFastProxy {
+					assert.Contains(t, r.Header, "X-Traefik-Fast-Proxy")
+				} else {
+					assert.NotContains(t, r.Header, "X-Traefik-Fast-Proxy")
+				}
+			})
+
+			var server *httptest.Server
+
+			if test.https {
+				server = httptest.NewUnstartedServer(handler)
+				server.EnableHTTP2 = false
+				server.StartTLS()
+
+				certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: server.TLS.Certificates[0].Certificate[0]})
+				test.serversTransport.RootCAs = []types.FileOrContent{
+					types.FileOrContent(certPEM),
+				}
+			} else {
+				server = httptest.NewServer(h2c.NewHandler(handler, &http2.Server{}))
+			}
+			t.Cleanup(func() {
+				server.Close()
+			})
+
+			targetURL := testhelpers.MustParseURL(server.URL)
+			if test.h2c {
+				targetURL.Scheme = "h2c"
+			}
+
+			serversTransports := map[string]*dynamic.ServersTransport{
+				"test": &test.serversTransport,
+			}
+
+			transportManager := service.NewTransportManager(nil)
+			transportManager.Update(serversTransports)
+
+			httpProxyBuilder := httputil.NewProxyBuilder(transportManager, nil)
+			proxyBuilder := NewSmartBuilder(transportManager, httpProxyBuilder, test.fastProxyConfig)
+
+			proxyHandler, err := proxyBuilder.Build("test", targetURL, false, false, time.Second)
+			require.NoError(t, err)
+
+			rw := httptest.NewRecorder()
+			proxyHandler.ServeHTTP(rw, httptest.NewRequest(http.MethodGet, "/", http.NoBody))
+
+			assert.Equal(t, 1, callCount)
+		})
+	}
+}

pkg/server/router/router_test.go

@@ -2,10 +2,12 @@ package router
 
 import (
 	"context"
+	"crypto/tls"
 	"io"
 	"math"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"strings"
 	"testing"
 	"time"
@@ -18,7 +20,7 @@ import (
 	"github.com/traefik/traefik/v3/pkg/server/middleware"
 	"github.com/traefik/traefik/v3/pkg/server/service"
 	"github.com/traefik/traefik/v3/pkg/testhelpers"
-	"github.com/traefik/traefik/v3/pkg/tls"
+	traefiktls "github.com/traefik/traefik/v3/pkg/tls"
 )
 
 func TestRouterManager_Get(t *testing.T) {
@@ -309,11 +311,12 @@ func TestRouterManager_Get(t *testing.T) {
 				},
 			})
 
-			roundTripperManager := service.NewRoundTripperManager(nil)
+			transportManager := service.NewTransportManager(nil)
-			roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+			transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-			serviceManager := service.NewManager(rtConf.Services, nil, nil, roundTripperManager)
+
+			serviceManager := service.NewManager(rtConf.Services, nil, nil, transportManager, proxyBuilderMock{})
 			middlewaresBuilder := middleware.NewBuilder(rtConf.Middlewares, serviceManager, nil)
-			tlsManager := tls.NewManager()
+			tlsManager := traefiktls.NewManager()
 
 			routerManager := NewManager(rtConf, serviceManager, middlewaresBuilder, nil, tlsManager)
 
@@ -340,7 +343,7 @@ func TestRuntimeConfiguration(t *testing.T) {
 		serviceConfig    map[string]*dynamic.Service
 		routerConfig     map[string]*dynamic.Router
 		middlewareConfig map[string]*dynamic.Middleware
-		tlsOptions       map[string]tls.Options
+		tlsOptions       map[string]traefiktls.Options
 		expectedError    int
 	}{
 		{
@@ -597,7 +600,7 @@ func TestRuntimeConfiguration(t *testing.T) {
 					TLS:         &dynamic.RouterTLSConfig{},
 				},
 			},
-			tlsOptions:    map[string]tls.Options{},
+			tlsOptions:    map[string]traefiktls.Options{},
 			expectedError: 1,
 		},
 		{
@@ -624,9 +627,9 @@ func TestRuntimeConfiguration(t *testing.T) {
 					},
 				},
 			},
-			tlsOptions: map[string]tls.Options{
+			tlsOptions: map[string]traefiktls.Options{
 				"broken-tlsOption": {
-					ClientAuth: tls.ClientAuth{
+					ClientAuth: traefiktls.ClientAuth{
 						ClientAuthType: "foobar",
 					},
 				},
@@ -655,9 +658,9 @@ func TestRuntimeConfiguration(t *testing.T) {
 					TLS:         &dynamic.RouterTLSConfig{},
 				},
 			},
-			tlsOptions: map[string]tls.Options{
+			tlsOptions: map[string]traefiktls.Options{
 				"default": {
-					ClientAuth: tls.ClientAuth{
+					ClientAuth: traefiktls.ClientAuth{
 						ClientAuthType: "foobar",
 					},
 				},
@@ -682,11 +685,12 @@ func TestRuntimeConfiguration(t *testing.T) {
 				},
 			})
 
-			roundTripperManager := service.NewRoundTripperManager(nil)
+			transportManager := service.NewTransportManager(nil)
-			roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+			transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-			serviceManager := service.NewManager(rtConf.Services, nil, nil, roundTripperManager)
+
+			serviceManager := service.NewManager(rtConf.Services, nil, nil, transportManager, proxyBuilderMock{})
 			middlewaresBuilder := middleware.NewBuilder(rtConf.Middlewares, serviceManager, nil)
-			tlsManager := tls.NewManager()
+			tlsManager := traefiktls.NewManager()
 			tlsManager.UpdateConfigs(context.Background(), nil, test.tlsOptions, nil)
 
 			routerManager := NewManager(rtConf, serviceManager, middlewaresBuilder, nil, tlsManager)
@@ -759,11 +763,12 @@ func TestProviderOnMiddlewares(t *testing.T) {
 		},
 	})
 
-	roundTripperManager := service.NewRoundTripperManager(nil)
+	transportManager := service.NewTransportManager(nil)
-	roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+	transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-	serviceManager := service.NewManager(rtConf.Services, nil, nil, roundTripperManager)
+
+	serviceManager := service.NewManager(rtConf.Services, nil, nil, transportManager, nil)
 	middlewaresBuilder := middleware.NewBuilder(rtConf.Middlewares, serviceManager, nil)
-	tlsManager := tls.NewManager()
+	tlsManager := traefiktls.NewManager()
 
 	routerManager := NewManager(rtConf, serviceManager, middlewaresBuilder, nil, tlsManager)
 
@@ -775,14 +780,22 @@ func TestProviderOnMiddlewares(t *testing.T) {
 	assert.Equal(t, []string{"m1@docker", "m2@docker", "m1@file"}, rtConf.Middlewares["chain@docker"].Chain.Middlewares)
 }
 
-type staticRoundTripperGetter struct {
+type staticTransportManager struct {
 	res *http.Response
 }
 
-func (s staticRoundTripperGetter) Get(name string) (http.RoundTripper, error) {
+func (s staticTransportManager) GetRoundTripper(_ string) (http.RoundTripper, error) {
 	return &staticTransport{res: s.res}, nil
 }
 
+func (s staticTransportManager) GetTLSConfig(_ string) (*tls.Config, error) {
+	panic("implement me")
+}
+
+func (s staticTransportManager) Get(_ string) (*dynamic.ServersTransport, error) {
+	panic("implement me")
+}
+
 type staticTransport struct {
 	res *http.Response
 }
@@ -829,9 +842,9 @@ func BenchmarkRouterServe(b *testing.B) {
 		},
 	})
 
-	serviceManager := service.NewManager(rtConf.Services, nil, nil, staticRoundTripperGetter{res})
+	serviceManager := service.NewManager(rtConf.Services, nil, nil, staticTransportManager{res}, nil)
 	middlewaresBuilder := middleware.NewBuilder(rtConf.Middlewares, serviceManager, nil)
-	tlsManager := tls.NewManager()
+	tlsManager := traefiktls.NewManager()
 
 	routerManager := NewManager(rtConf, serviceManager, middlewaresBuilder, nil, tlsManager)
 
@@ -871,7 +884,7 @@ func BenchmarkService(b *testing.B) {
 		},
 	})
 
-	serviceManager := service.NewManager(rtConf.Services, nil, nil, staticRoundTripperGetter{res})
+	serviceManager := service.NewManager(rtConf.Services, nil, nil, staticTransportManager{res}, nil)
 	w := httptest.NewRecorder()
 	req := testhelpers.MustNewRequest(http.MethodGet, "http://foo.bar/", nil)
 
@@ -881,3 +894,13 @@ func BenchmarkService(b *testing.B) {
 		handler.ServeHTTP(w, req)
 	}
 }
+
+type proxyBuilderMock struct{}
+
+func (p proxyBuilderMock) Build(_ string, _ *url.URL, _, _ bool, _ time.Duration) (http.Handler, error) {
+	return http.HandlerFunc(func(responseWriter http.ResponseWriter, req *http.Request) {}), nil
+}
+
+func (p proxyBuilderMock) Update(_ map[string]*dynamic.ServersTransport) {
+	panic("implement me")
+}

pkg/server/routerfactory_test.go

@@ -3,7 +3,9 @@ package server
 import (
 	"net/http"
 	"net/http/httptest"
+	"net/url"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
@@ -48,9 +50,10 @@ func TestReuseService(t *testing.T) {
 		),
 	)
 
-	roundTripperManager := service.NewRoundTripperManager(nil)
+	transportManager := service.NewTransportManager(nil)
-	roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+	transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-	managerFactory := service.NewManagerFactory(staticConfig, nil, nil, roundTripperManager, nil)
+
+	managerFactory := service.NewManagerFactory(staticConfig, nil, nil, transportManager, proxyBuilderMock{}, nil)
 	tlsManager := tls.NewManager()
 
 	dialerManager := tcp.NewDialerManager(nil)
@@ -184,9 +187,10 @@ func TestServerResponseEmptyBackend(t *testing.T) {
 				},
 			}
 
-			roundTripperManager := service.NewRoundTripperManager(nil)
+			transportManager := service.NewTransportManager(nil)
-			roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+			transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-			managerFactory := service.NewManagerFactory(staticConfig, nil, nil, roundTripperManager, nil)
+
+			managerFactory := service.NewManagerFactory(staticConfig, nil, nil, transportManager, proxyBuilderMock{}, nil)
 			tlsManager := tls.NewManager()
 
 			dialerManager := tcp.NewDialerManager(nil)
@@ -228,9 +232,10 @@ func TestInternalServices(t *testing.T) {
 		),
 	)
 
-	roundTripperManager := service.NewRoundTripperManager(nil)
+	transportManager := service.NewTransportManager(nil)
-	roundTripperManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
+	transportManager.Update(map[string]*dynamic.ServersTransport{"default@internal": {}})
-	managerFactory := service.NewManagerFactory(staticConfig, nil, nil, roundTripperManager, nil)
+
+	managerFactory := service.NewManagerFactory(staticConfig, nil, nil, transportManager, nil, nil)
 	tlsManager := tls.NewManager()
 
 	dialerManager := tcp.NewDialerManager(nil)
@@ -246,3 +251,13 @@ func TestInternalServices(t *testing.T) {
 
 	assert.Equal(t, http.StatusOK, responseRecorderOk.Result().StatusCode, "status code")
 }
+
+type proxyBuilderMock struct{}
+
+func (p proxyBuilderMock) Build(_ string, _ *url.URL, _, _ bool, _ time.Duration) (http.Handler, error) {
+	return http.HandlerFunc(func(responseWriter http.ResponseWriter, req *http.Request) {}), nil
+}
+
+func (p proxyBuilderMock) Update(_ map[string]*dynamic.ServersTransport) {
+	panic("implement me")
+}

pkg/server/service/managerfactory.go

@@ -17,7 +17,8 @@ import (
 type ManagerFactory struct {
 	observabilityMgr *middleware.ObservabilityMgr
 
-	roundTripperManager *RoundTripperManager
+	transportManager *TransportManager
+	proxyBuilder     ProxyBuilder
 
 	api              func(configuration *runtime.Configuration) http.Handler
 	restHandler      http.Handler
@@ -30,12 +31,13 @@ type ManagerFactory struct {
 }
 
 // NewManagerFactory creates a new ManagerFactory.
-func NewManagerFactory(staticConfiguration static.Configuration, routinesPool *safe.Pool, observabilityMgr *middleware.ObservabilityMgr, roundTripperManager *RoundTripperManager, acmeHTTPHandler http.Handler) *ManagerFactory {
+func NewManagerFactory(staticConfiguration static.Configuration, routinesPool *safe.Pool, observabilityMgr *middleware.ObservabilityMgr, transportManager *TransportManager, proxyBuilder ProxyBuilder, acmeHTTPHandler http.Handler) *ManagerFactory {
 	factory := &ManagerFactory{
-		observabilityMgr:    observabilityMgr,
+		observabilityMgr: observabilityMgr,
-		routinesPool:        routinesPool,
+		routinesPool:     routinesPool,
-		roundTripperManager: roundTripperManager,
+		transportManager: transportManager,
-		acmeHTTPHandler:     acmeHTTPHandler,
+		proxyBuilder:     proxyBuilder,
+		acmeHTTPHandler:  acmeHTTPHandler,
 	}
 
 	if staticConfiguration.API != nil {
@@ -73,7 +75,7 @@ func NewManagerFactory(staticConfiguration static.Configuration, routinesPool *s
 
 // Build creates a service manager.
 func (f *ManagerFactory) Build(configuration *runtime.Configuration) *InternalHandlers {
-	svcManager := NewManager(configuration.Services, f.observabilityMgr, f.routinesPool, f.roundTripperManager)
+	svcManager := NewManager(configuration.Services, f.observabilityMgr, f.routinesPool, f.transportManager, f.proxyBuilder)
 
 	var apiHandler http.Handler
 	if f.api != nil {

pkg/server/service/proxy_test.go

@@ -1,37 +0,0 @@
-package service
-
-import (
-	"io"
-	"net/http"
-	"net/http/httptest"
-	"strings"
-	"testing"
-
-	"github.com/traefik/traefik/v3/pkg/testhelpers"
-)
-
-type staticTransport struct {
-	res *http.Response
-}
-
-func (t *staticTransport) RoundTrip(r *http.Request) (*http.Response, error) {
-	return t.res, nil
-}
-
-func BenchmarkProxy(b *testing.B) {
-	res := &http.Response{
-		StatusCode: http.StatusOK,
-		Body:       io.NopCloser(strings.NewReader("")),
-	}
-
-	w := httptest.NewRecorder()
-	req := testhelpers.MustNewRequest(http.MethodGet, "http://foo.bar/", nil)
-
-	pool := newBufferPool()
-	handler := buildSingleHostProxy(req.URL, false, 0, &staticTransport{res}, pool)
-
-	b.ReportAllocs()
-	for range b.N {
-		handler.ServeHTTP(w, req)
-	}
-}

pkg/server/service/service.go

@@ -9,7 +9,6 @@ import (
 	"hash/fnv"
 	"math/rand"
 	"net/http"
-	"net/http/httputil"
 	"net/url"
 	"reflect"
 	"strings"
@@ -25,6 +24,7 @@ import (
 	"github.com/traefik/traefik/v3/pkg/middlewares/capture"
 	metricsMiddle "github.com/traefik/traefik/v3/pkg/middlewares/metrics"
 	"github.com/traefik/traefik/v3/pkg/middlewares/observability"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
 	"github.com/traefik/traefik/v3/pkg/safe"
 	"github.com/traefik/traefik/v3/pkg/server/cookie"
 	"github.com/traefik/traefik/v3/pkg/server/middleware"
@@ -40,17 +40,18 @@ const (
 	defaultMaxBodySize int64 = -1
 )
 
-// RoundTripperGetter is a roundtripper getter interface.
+// ProxyBuilder builds reverse proxy handlers.
-type RoundTripperGetter interface {
+type ProxyBuilder interface {
-	Get(name string) (http.RoundTripper, error)
+	Build(cfgName string, targetURL *url.URL, shouldObserve, passHostHeader bool, flushInterval time.Duration) (http.Handler, error)
+	Update(configs map[string]*dynamic.ServersTransport)
 }
 
 // Manager The service manager.
 type Manager struct {
-	routinePool         *safe.Pool
+	routinePool      *safe.Pool
-	observabilityMgr    *middleware.ObservabilityMgr
+	observabilityMgr *middleware.ObservabilityMgr
-	bufferPool          httputil.BufferPool
+	transportManager httputil.TransportManager
-	roundTripperManager RoundTripperGetter
+	proxyBuilder     ProxyBuilder
 
 	services       map[string]http.Handler
 	configs        map[string]*runtime.ServiceInfo
@@ -59,16 +60,16 @@ type Manager struct {
 }
 
 // NewManager creates a new Manager.
-func NewManager(configs map[string]*runtime.ServiceInfo, observabilityMgr *middleware.ObservabilityMgr, routinePool *safe.Pool, roundTripperManager RoundTripperGetter) *Manager {
+func NewManager(configs map[string]*runtime.ServiceInfo, observabilityMgr *middleware.ObservabilityMgr, routinePool *safe.Pool, transportManager httputil.TransportManager, proxyBuilder ProxyBuilder) *Manager {
 	return &Manager{
-		routinePool:         routinePool,
+		routinePool:      routinePool,
-		observabilityMgr:    observabilityMgr,
+		observabilityMgr: observabilityMgr,
-		bufferPool:          newBufferPool(),
+		transportManager: transportManager,
-		roundTripperManager: roundTripperManager,
+		proxyBuilder:     proxyBuilder,
-		services:            make(map[string]http.Handler),
+		services:         make(map[string]http.Handler),
-		configs:             configs,
+		configs:          configs,
-		healthCheckers:      make(map[string]*healthcheck.ServiceHealthChecker),
+		healthCheckers:   make(map[string]*healthcheck.ServiceHealthChecker),
-		rand:                rand.New(rand.NewSource(time.Now().UnixNano())),
+		rand:             rand.New(rand.NewSource(time.Now().UnixNano())),
 	}
 }
 
@@ -298,9 +299,9 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 	logger.Debug().Msg("Creating load-balancer")
 
 	// TODO: should we keep this config value as Go is now handling stream response correctly?
-	flushInterval := dynamic.DefaultFlushInterval
+	flushInterval := time.Duration(dynamic.DefaultFlushInterval)
 	if service.ResponseForwarding != nil {
-		flushInterval = service.ResponseForwarding.FlushInterval
+		flushInterval = time.Duration(service.ResponseForwarding.FlushInterval)
 	}
 
 	if len(service.ServersTransport) > 0 {
@@ -317,11 +318,6 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 		passHostHeader = *service.PassHostHeader
 	}
 
-	roundTripper, err := m.roundTripperManager.Get(service.ServersTransport)
-	if err != nil {
-		return nil, err
-	}
-
 	lb := wrr.New(service.Sticky, service.HealthCheck != nil)
 	healthCheckTargets := make(map[string]*url.URL)
 
@@ -341,14 +337,12 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 
 		qualifiedSvcName := provider.GetQualifiedName(ctx, serviceName)
 
-		if m.observabilityMgr.ShouldAddTracing(qualifiedSvcName) || m.observabilityMgr.ShouldAddMetrics(qualifiedSvcName) {
+		shouldObserve := m.observabilityMgr.ShouldAddTracing(qualifiedSvcName) || m.observabilityMgr.ShouldAddMetrics(qualifiedSvcName)
-			// Wrapping the roundTripper with the Tracing roundTripper,
+		proxy, err := m.proxyBuilder.Build(service.ServersTransport, target, shouldObserve, passHostHeader, flushInterval)
-			// to handle the reverseProxy client span creation.
+		if err != nil {
-			roundTripper = newObservabilityRoundTripper(m.observabilityMgr.SemConvMetricsRegistry(), roundTripper)
+			return nil, fmt.Errorf("error building proxy for server URL %s: %w", server.URL, err)
 		}
 
-		proxy := buildSingleHostProxy(target, passHostHeader, time.Duration(flushInterval), roundTripper, m.bufferPool)
-
 		// Prevents from enabling observability for internal resources.
 
 		if m.observabilityMgr.ShouldAddAccessLogs(qualifiedSvcName) {
@@ -393,6 +387,11 @@ func (m *Manager) getLoadBalancerServiceHandler(ctx context.Context, serviceName
 	}
 
 	if service.HealthCheck != nil {
+		roundTripper, err := m.transportManager.GetRoundTripper(service.ServersTransport)
+		if err != nil {
+			return nil, fmt.Errorf("getting RoundTripper: %w", err)
+		}
+
 		m.healthCheckers[serviceName] = healthcheck.NewServiceHealthChecker(
 			ctx,
 			m.observabilityMgr.MetricsRegistry(),

pkg/server/service/service_test.go

@@ -2,6 +2,7 @@ package service
 
 import (
 	"context"
+	"crypto/tls"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -14,13 +15,14 @@ import (
 	"github.com/stretchr/testify/require"
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
 	"github.com/traefik/traefik/v3/pkg/config/runtime"
+	"github.com/traefik/traefik/v3/pkg/proxy/httputil"
 	"github.com/traefik/traefik/v3/pkg/server/provider"
 	"github.com/traefik/traefik/v3/pkg/testhelpers"
 )
 
 func TestGetLoadBalancer(t *testing.T) {
 	sm := Manager{
-		roundTripperManager: newRtMock(),
+		transportManager: &transportManagerMock{},
 	}
 
 	testCases := []struct {
@@ -40,14 +42,14 @@ func TestGetLoadBalancer(t *testing.T) {
 					},
 				},
 			},
-			fwd:         &MockForwarder{},
+			fwd:         &forwarderMock{},
 			expectError: true,
 		},
 		{
 			desc:        "Succeeds when there are no servers",
 			serviceName: "test",
 			service:     &dynamic.ServersLoadBalancer{},
-			fwd:         &MockForwarder{},
+			fwd:         &forwarderMock{},
 			expectError: false,
 		},
 		{
@@ -56,7 +58,7 @@ func TestGetLoadBalancer(t *testing.T) {
 			service: &dynamic.ServersLoadBalancer{
 				Sticky: &dynamic.Sticky{Cookie: &dynamic.Cookie{}},
 			},
-			fwd:         &MockForwarder{},
+			fwd:         &forwarderMock{},
 			expectError: false,
 		},
 	}
@@ -79,11 +81,8 @@ func TestGetLoadBalancer(t *testing.T) {
 }
 
 func TestGetLoadBalancerServiceHandler(t *testing.T) {
-	sm := NewManager(nil, nil, nil, &RoundTripperManager{
+	pb := httputil.NewProxyBuilder(&transportManagerMock{}, nil)
-		roundTrippers: map[string]http.RoundTripper{
+	sm := NewManager(nil, nil, nil, transportManagerMock{}, pb)
-			"default@internal": http.DefaultTransport,
-		},
-	})
 
 	server1 := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("X-From", "first")
@@ -139,7 +138,7 @@ func TestGetLoadBalancerServiceHandler(t *testing.T) {
 			desc:        "Load balances between the two servers",
 			serviceName: "test",
 			service: &dynamic.ServersLoadBalancer{
-				PassHostHeader: Bool(true),
+				PassHostHeader: boolPtr(true),
 				Servers: []dynamic.Server{
 					{
 						URL: server1.URL,
@@ -254,7 +253,7 @@ func TestGetLoadBalancerServiceHandler(t *testing.T) {
 			desc:        "PassHost doesn't pass the host instead of the IP",
 			serviceName: "test",
 			service: &dynamic.ServersLoadBalancer{
-				PassHostHeader: Bool(false),
+				PassHostHeader: boolPtr(false),
 				Sticky:         &dynamic.Sticky{Cookie: &dynamic.Cookie{}},
 				Servers: []dynamic.Server{
 					{
@@ -359,11 +358,8 @@ func TestGetLoadBalancerServiceHandler(t *testing.T) {
 
 // This test is an adapted version of net/http/httputil.Test1xxResponses test.
 func Test1xxResponses(t *testing.T) {
-	sm := NewManager(nil, nil, nil, &RoundTripperManager{
+	pb := httputil.NewProxyBuilder(&transportManagerMock{}, nil)
-		roundTrippers: map[string]http.RoundTripper{
+	sm := NewManager(nil, nil, nil, &transportManagerMock{}, pb)
-			"default@internal": http.DefaultTransport,
-		},
-	})
 
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		h := w.Header()
@@ -499,11 +495,7 @@ func TestManager_Build(t *testing.T) {
 		t.Run(test.desc, func(t *testing.T) {
 			t.Parallel()
 
-			manager := NewManager(test.configs, nil, nil, &RoundTripperManager{
+			manager := NewManager(test.configs, nil, nil, &transportManagerMock{}, nil)
-				roundTrippers: map[string]http.RoundTripper{
-					"default@internal": http.DefaultTransport,
-				},
-			})
 
 			ctx := context.Background()
 			if len(test.providerName) > 0 {
@@ -526,30 +518,30 @@ func TestMultipleTypeOnBuildHTTP(t *testing.T) {
 		},
 	}
 
-	manager := NewManager(services, nil, nil, &RoundTripperManager{
+	manager := NewManager(services, nil, nil, &transportManagerMock{}, nil)
-		roundTrippers: map[string]http.RoundTripper{
-			"default@internal": http.DefaultTransport,
-		},
-	})
 
 	_, err := manager.BuildHTTP(context.Background(), "test@file")
 	assert.Error(t, err, "cannot create service: multi-types service not supported, consider declaring two different pieces of service instead")
 }
 
-func Bool(v bool) *bool { return &v }
+func boolPtr(v bool) *bool { return &v }
 
-type MockForwarder struct{}
+type forwarderMock struct{}
 
-func (MockForwarder) ServeHTTP(http.ResponseWriter, *http.Request) {
+func (forwarderMock) ServeHTTP(http.ResponseWriter, *http.Request) {
 	panic("not available")
 }
 
-type rtMock struct{}
+type transportManagerMock struct{}
 
-func newRtMock() RoundTripperGetter {
+func (t transportManagerMock) GetRoundTripper(_ string) (http.RoundTripper, error) {
-	return &rtMock{}
+	return &http.Transport{}, nil
 }
 
-func (r *rtMock) Get(_ string) (http.RoundTripper, error) {
+func (t transportManagerMock) GetTLSConfig(_ string) (*tls.Config, error) {
-	return http.DefaultTransport, nil
+	return nil, nil
+}
+
+func (t transportManagerMock) Get(_ string) (*dynamic.ServersTransport, error) {
+	return &dynamic.ServersTransport{}, nil
 }

pkg/server/service/smart_roundtripper.go

@@ -11,6 +11,15 @@ import (
 	"golang.org/x/net/http2"
 )
 
+type h2cTransportWrapper struct {
+	*http2.Transport
+}
+
+func (t *h2cTransportWrapper) RoundTrip(req *http.Request) (*http.Response, error) {
+	req.URL.Scheme = "http"
+	return t.Transport.RoundTrip(req)
+}
+
 func newSmartRoundTripper(transport *http.Transport, forwardingTimeouts *dynamic.ForwardingTimeouts) (*smartRoundTripper, error) {
 	transportHTTP1 := transport.Clone()
 

pkg/server/service/transport.go

@@ -22,52 +22,45 @@ import (
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
 	traefiktls "github.com/traefik/traefik/v3/pkg/tls"
 	"github.com/traefik/traefik/v3/pkg/types"
-	"golang.org/x/net/http2"
 )
 
-type h2cTransportWrapper struct {
-	*http2.Transport
-}
-
-func (t *h2cTransportWrapper) RoundTrip(req *http.Request) (*http.Response, error) {
-	req.URL.Scheme = "http"
-	return t.Transport.RoundTrip(req)
-}
-
 // SpiffeX509Source allows to retrieve a x509 SVID and bundle.
 type SpiffeX509Source interface {
 	x509svid.Source
 	x509bundle.Source
 }
 
-// NewRoundTripperManager creates a new RoundTripperManager.
+// TransportManager handles transports for backend communication.
-func NewRoundTripperManager(spiffeX509Source SpiffeX509Source) *RoundTripperManager {
+type TransportManager struct {
-	return &RoundTripperManager{
-		roundTrippers:    make(map[string]http.RoundTripper),
-		configs:          make(map[string]*dynamic.ServersTransport),
-		spiffeX509Source: spiffeX509Source,
-	}
-}
-
-// RoundTripperManager handles roundtripper for the reverse proxy.
-type RoundTripperManager struct {
 	rtLock        sync.RWMutex
 	roundTrippers map[string]http.RoundTripper
 	configs       map[string]*dynamic.ServersTransport
+	tlsConfigs    map[string]*tls.Config
 
 	spiffeX509Source SpiffeX509Source
 }
 
-// Update updates the roundtrippers configurations.
+// NewTransportManager creates a new TransportManager.
-func (r *RoundTripperManager) Update(newConfigs map[string]*dynamic.ServersTransport) {
+func NewTransportManager(spiffeX509Source SpiffeX509Source) *TransportManager {
-	r.rtLock.Lock()
+	return &TransportManager{
-	defer r.rtLock.Unlock()
+		roundTrippers:    make(map[string]http.RoundTripper),
+		configs:          make(map[string]*dynamic.ServersTransport),
+		tlsConfigs:       make(map[string]*tls.Config),
+		spiffeX509Source: spiffeX509Source,
+	}
+}
 
-	for configName, config := range r.configs {
+// Update updates the transport configurations.
+func (t *TransportManager) Update(newConfigs map[string]*dynamic.ServersTransport) {
+	t.rtLock.Lock()
+	defer t.rtLock.Unlock()
+
+	for configName, config := range t.configs {
 		newConfig, ok := newConfigs[configName]
 		if !ok {
-			delete(r.configs, configName)
+			delete(t.configs, configName)
-			delete(r.roundTrippers, configName)
+			delete(t.roundTrippers, configName)
+			delete(t.tlsConfigs, configName)
 			continue
 		}
 
@@ -76,50 +69,133 @@ func (r *RoundTripperManager) Update(newConfigs map[string]*dynamic.ServersTrans
 		}
 
 		var err error
-		r.roundTrippers[configName], err = r.createRoundTripper(newConfig)
+
+		var tlsConfig *tls.Config
+		if tlsConfig, err = t.createTLSConfig(newConfig); err != nil {
+			log.Error().Err(err).Msgf("Could not configure HTTP Transport %s TLS configuration, fallback on default TLS config", configName)
+		}
+		t.tlsConfigs[configName] = tlsConfig
+
+		t.roundTrippers[configName], err = t.createRoundTripper(newConfig, tlsConfig)
 		if err != nil {
 			log.Error().Err(err).Msgf("Could not configure HTTP Transport %s, fallback on default transport", configName)
-			r.roundTrippers[configName] = http.DefaultTransport
+			t.roundTrippers[configName] = http.DefaultTransport
 		}
 	}
 
 	for newConfigName, newConfig := range newConfigs {
-		if _, ok := r.configs[newConfigName]; ok {
+		if _, ok := t.configs[newConfigName]; ok {
 			continue
 		}
 
 		var err error
-		r.roundTrippers[newConfigName], err = r.createRoundTripper(newConfig)
+
+		var tlsConfig *tls.Config
+		if tlsConfig, err = t.createTLSConfig(newConfig); err != nil {
+			log.Error().Err(err).Msgf("Could not configure HTTP Transport %s TLS configuration, fallback on default TLS config", newConfigName)
+		}
+		t.tlsConfigs[newConfigName] = tlsConfig
+
+		t.roundTrippers[newConfigName], err = t.createRoundTripper(newConfig, tlsConfig)
 		if err != nil {
 			log.Error().Err(err).Msgf("Could not configure HTTP Transport %s, fallback on default transport", newConfigName)
-			r.roundTrippers[newConfigName] = http.DefaultTransport
+			t.roundTrippers[newConfigName] = http.DefaultTransport
 		}
 	}
 
-	r.configs = newConfigs
+	t.configs = newConfigs
 }
 
-// Get gets a roundtripper by name.
+// GetRoundTripper gets a roundtripper corresponding to the given transport name.
-func (r *RoundTripperManager) Get(name string) (http.RoundTripper, error) {
+func (t *TransportManager) GetRoundTripper(name string) (http.RoundTripper, error) {
 	if len(name) == 0 {
 		name = "default@internal"
 	}
 
-	r.rtLock.RLock()
+	t.rtLock.RLock()
-	defer r.rtLock.RUnlock()
+	defer t.rtLock.RUnlock()
 
-	if rt, ok := r.roundTrippers[name]; ok {
+	if rt, ok := t.roundTrippers[name]; ok {
 		return rt, nil
 	}
 
 	return nil, fmt.Errorf("servers transport not found %s", name)
 }
 
+// Get gets transport by name.
+func (t *TransportManager) Get(name string) (*dynamic.ServersTransport, error) {
+	if len(name) == 0 {
+		name = "default@internal"
+	}
+
+	t.rtLock.RLock()
+	defer t.rtLock.RUnlock()
+
+	if rt, ok := t.configs[name]; ok {
+		return rt, nil
+	}
+
+	return nil, fmt.Errorf("servers transport not found %s", name)
+}
+
+// GetTLSConfig gets a TLS config  corresponding to the given transport name.
+func (t *TransportManager) GetTLSConfig(name string) (*tls.Config, error) {
+	if len(name) == 0 {
+		name = "default@internal"
+	}
+
+	t.rtLock.RLock()
+	defer t.rtLock.RUnlock()
+
+	if rt, ok := t.tlsConfigs[name]; ok {
+		return rt, nil
+	}
+
+	return nil, fmt.Errorf("tls config not found %s", name)
+}
+
+func (t *TransportManager) createTLSConfig(cfg *dynamic.ServersTransport) (*tls.Config, error) {
+	var config *tls.Config
+	if cfg.Spiffe != nil {
+		if t.spiffeX509Source == nil {
+			return nil, errors.New("SPIFFE is enabled for this transport, but not configured")
+		}
+
+		spiffeAuthorizer, err := buildSpiffeAuthorizer(cfg.Spiffe)
+		if err != nil {
+			return nil, fmt.Errorf("unable to build SPIFFE authorizer: %w", err)
+		}
+
+		config = tlsconfig.MTLSClientConfig(t.spiffeX509Source, t.spiffeX509Source, spiffeAuthorizer)
+	}
+
+	if cfg.InsecureSkipVerify || len(cfg.RootCAs) > 0 || len(cfg.ServerName) > 0 || len(cfg.Certificates) > 0 || cfg.PeerCertURI != "" {
+		if config != nil {
+			return nil, errors.New("TLS and SPIFFE configuration cannot be defined at the same time")
+		}
+
+		config = &tls.Config{
+			ServerName:         cfg.ServerName,
+			InsecureSkipVerify: cfg.InsecureSkipVerify,
+			RootCAs:            createRootCACertPool(cfg.RootCAs),
+			Certificates:       cfg.Certificates.GetCertificates(),
+		}
+
+		if cfg.PeerCertURI != "" {
+			config.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
+				return traefiktls.VerifyPeerCertificate(cfg.PeerCertURI, config, rawCerts)
+			}
+		}
+	}
+
+	return config, nil
+}
+
 // createRoundTripper creates an http.RoundTripper configured with the Transport configuration settings.
 // For the settings that can't be configured in Traefik it uses the default http.Transport settings.
 // An exception to this is the MaxIdleConns setting as we only provide the option MaxIdleConnsPerHost in Traefik at this point in time.
 // Setting this value to the default of 100 could lead to confusing behavior and backwards compatibility issues.
-func (r *RoundTripperManager) createRoundTripper(cfg *dynamic.ServersTransport) (http.RoundTripper, error) {
+func (t *TransportManager) createRoundTripper(cfg *dynamic.ServersTransport, tlsConfig *tls.Config) (http.RoundTripper, error) {
 	if cfg == nil {
 		return nil, errors.New("no transport configuration given")
 	}
@@ -142,6 +218,7 @@ func (r *RoundTripperManager) createRoundTripper(cfg *dynamic.ServersTransport)
 		ExpectContinueTimeout: 1 * time.Second,
 		ReadBufferSize:        64 * 1024,
 		WriteBufferSize:       64 * 1024,
+		TLSClientConfig:       tlsConfig,
 	}
 
 	if cfg.ForwardingTimeouts != nil {
@@ -149,41 +226,9 @@ func (r *RoundTripperManager) createRoundTripper(cfg *dynamic.ServersTransport)
 		transport.IdleConnTimeout = time.Duration(cfg.ForwardingTimeouts.IdleConnTimeout)
 	}
 
-	if cfg.Spiffe != nil {
-		if r.spiffeX509Source == nil {
-			return nil, errors.New("SPIFFE is enabled for this transport, but not configured")
-		}
-
-		spiffeAuthorizer, err := buildSpiffeAuthorizer(cfg.Spiffe)
-		if err != nil {
-			return nil, fmt.Errorf("unable to build SPIFFE authorizer: %w", err)
-		}
-
-		transport.TLSClientConfig = tlsconfig.MTLSClientConfig(r.spiffeX509Source, r.spiffeX509Source, spiffeAuthorizer)
-	}
-
-	if cfg.InsecureSkipVerify || len(cfg.RootCAs) > 0 || len(cfg.ServerName) > 0 || len(cfg.Certificates) > 0 || cfg.PeerCertURI != "" {
-		if transport.TLSClientConfig != nil {
-			return nil, errors.New("TLS and SPIFFE configuration cannot be defined at the same time")
-		}
-
-		transport.TLSClientConfig = &tls.Config{
-			ServerName:         cfg.ServerName,
-			InsecureSkipVerify: cfg.InsecureSkipVerify,
-			RootCAs:            createRootCACertPool(cfg.RootCAs),
-			Certificates:       cfg.Certificates.GetCertificates(),
-		}
-
-		if cfg.PeerCertURI != "" {
-			transport.TLSClientConfig.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
-				return traefiktls.VerifyPeerCertificate(cfg.PeerCertURI, transport.TLSClientConfig, rawCerts)
-			}
-		}
-	}
-
 	// Return directly HTTP/1.1 transport when HTTP/2 is disabled
 	if cfg.DisableHTTP2 {
-		return &KerberosRoundTripper{
+		return &kerberosRoundTripper{
 			OriginalRoundTripper: transport,
 			new: func() http.RoundTripper {
 				return transport.Clone()
@@ -195,7 +240,7 @@ func (r *RoundTripperManager) createRoundTripper(cfg *dynamic.ServersTransport)
 	if err != nil {
 		return nil, err
 	}
-	return &KerberosRoundTripper{
+	return &kerberosRoundTripper{
 		OriginalRoundTripper: rt,
 		new: func() http.RoundTripper {
 			return rt.Clone()
@@ -203,11 +248,6 @@ func (r *RoundTripperManager) createRoundTripper(cfg *dynamic.ServersTransport)
 	}, nil
 }
 
-type KerberosRoundTripper struct {
-	new                  func() http.RoundTripper
-	OriginalRoundTripper http.RoundTripper
-}
-
 type stickyRoundTripper struct {
 	RoundTripper http.RoundTripper
 }
@@ -220,7 +260,12 @@ func AddTransportOnContext(ctx context.Context) context.Context {
 	return context.WithValue(ctx, transportKey, &stickyRoundTripper{})
 }
 
-func (k *KerberosRoundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
+type kerberosRoundTripper struct {
+	new                  func() http.RoundTripper
+	OriginalRoundTripper http.RoundTripper
+}
+
+func (k *kerberosRoundTripper) RoundTrip(request *http.Request) (*http.Response, error) {
 	value, ok := request.Context().Value(transportKey).(*stickyRoundTripper)
 	if !ok {
 		return k.OriginalRoundTripper.RoundTrip(request)

pkg/server/service/transport_test.go

@@ -141,7 +141,7 @@ func TestKeepConnectionWhenSameConfiguration(t *testing.T) {
 	srv.TLS = &tls.Config{Certificates: []tls.Certificate{cert}}
 	srv.StartTLS()
 
-	rtManager := NewRoundTripperManager(nil)
+	transportManager := NewTransportManager(nil)
 
 	dynamicConf := map[string]*dynamic.ServersTransport{
 		"test": {
@@ -151,9 +151,9 @@ func TestKeepConnectionWhenSameConfiguration(t *testing.T) {
 	}
 
 	for range 10 {
-		rtManager.Update(dynamicConf)
+		transportManager.Update(dynamicConf)
 
-		tr, err := rtManager.Get("test")
+		tr, err := transportManager.GetRoundTripper("test")
 		require.NoError(t, err)
 
 		client := http.Client{Transport: tr}
@@ -173,9 +173,9 @@ func TestKeepConnectionWhenSameConfiguration(t *testing.T) {
 		},
 	}
 
-	rtManager.Update(dynamicConf)
+	transportManager.Update(dynamicConf)
 
-	tr, err := rtManager.Get("test")
+	tr, err := transportManager.GetRoundTripper("test")
 	require.NoError(t, err)
 
 	client := http.Client{Transport: tr}
@@ -209,7 +209,7 @@ func TestMTLS(t *testing.T) {
 	}
 	srv.StartTLS()
 
-	rtManager := NewRoundTripperManager(nil)
+	transportManager := NewTransportManager(nil)
 
 	dynamicConf := map[string]*dynamic.ServersTransport{
 		"test": {
@@ -227,9 +227,9 @@ func TestMTLS(t *testing.T) {
 		},
 	}
 
-	rtManager.Update(dynamicConf)
+	transportManager.Update(dynamicConf)
 
-	tr, err := rtManager.Get("test")
+	tr, err := transportManager.GetRoundTripper("test")
 	require.NoError(t, err)
 
 	client := http.Client{Transport: tr}
@@ -348,7 +348,7 @@ func TestSpiffeMTLS(t *testing.T) {
 
 	for _, test := range testCases {
 		t.Run(test.desc, func(t *testing.T) {
-			rtManager := NewRoundTripperManager(test.clientSource)
+			transportManager := NewTransportManager(test.clientSource)
 
 			dynamicConf := map[string]*dynamic.ServersTransport{
 				"test": {
@@ -356,9 +356,9 @@ func TestSpiffeMTLS(t *testing.T) {
 				},
 			}
 
-			rtManager.Update(dynamicConf)
+			transportManager.Update(dynamicConf)
 
-			tr, err := rtManager.Get("test")
+			tr, err := transportManager.GetRoundTripper("test")
 			require.NoError(t, err)
 
 			client := http.Client{Transport: tr}
@@ -415,7 +415,7 @@ func TestDisableHTTP2(t *testing.T) {
 			srv.EnableHTTP2 = test.serverHTTP2
 			srv.StartTLS()
 
-			rtManager := NewRoundTripperManager(nil)
+			transportManager := NewTransportManager(nil)
 
 			dynamicConf := map[string]*dynamic.ServersTransport{
 				"test": {
@@ -424,9 +424,9 @@ func TestDisableHTTP2(t *testing.T) {
 				},
 			}
 
-			rtManager.Update(dynamicConf)
+			transportManager.Update(dynamicConf)
 
-			tr, err := rtManager.Get("test")
+			tr, err := transportManager.GetRoundTripper("test")
 			require.NoError(t, err)
 
 			client := http.Client{Transport: tr}
@@ -593,7 +593,7 @@ func TestKerberosRoundTripper(t *testing.T) {
 
 			origCount := 0
 			dedicatedCount := 0
-			rt := KerberosRoundTripper{
+			rt := kerberosRoundTripper{
 				new: func() http.RoundTripper {
 					return roundTripperFn(func(req *http.Request) (*http.Response, error) {
 						dedicatedCount++