Make the behavior of prefix matching in Ingress consistent with Kubernetes doc

pkg/provider/kubernetes/ingress/fixtures/Ingress-with-strict-prefix-matching.yml

@@ -0,0 +1,49 @@
+kind: Ingress
+apiVersion: networking.k8s.io/v1
+metadata:
+  name: ""
+  namespace: testing
+
+spec:
+  rules:
+    - http:
+        paths:
+          - path: /bar
+            backend:
+              service:
+                name: service1
+                port:
+                  number: 80
+            pathType: Prefix
+
+---
+kind: Service
+apiVersion: v1
+metadata:
+  name: service1
+  namespace: testing
+
+spec:
+  ports:
+    - port: 80
+  clusterIP: 10.0.0.1
+
+---
+kind: EndpointSlice
+apiVersion: discovery.k8s.io/v1
+metadata:
+  name: service1-abc
+  namespace: testing
+  labels:
+    kubernetes.io/service-name: service1
+
+addressType: IPv4
+ports:
+  - port: 8080
+    name: ""
+endpoints:
+  - addresses:
+      - 10.10.0.1
+      - 10.21.0.1
+    conditions:
+      ready: true

pkg/provider/kubernetes/ingress/kubernetes.go

@@ -56,6 +56,7 @@ type Provider struct {
 	DisableIngressClassLookup    bool `description:"Disables the lookup of IngressClasses (Deprecated, please use DisableClusterScopeResources)." json:"disableIngressClassLookup,omitempty" toml:"disableIngressClassLookup,omitempty" yaml:"disableIngressClassLookup,omitempty" export:"true"`
 	DisableClusterScopeResources bool `description:"Disables the lookup of cluster scope resources (incompatible with IngressClasses and NodePortLB enabled services)." json:"disableClusterScopeResources,omitempty" toml:"disableClusterScopeResources,omitempty" yaml:"disableClusterScopeResources,omitempty" export:"true"`
 	NativeLBByDefault            bool `description:"Defines whether to use Native Kubernetes load-balancing mode by default." json:"nativeLBByDefault,omitempty" toml:"nativeLBByDefault,omitempty" yaml:"nativeLBByDefault,omitempty" export:"true"`
+	StrictPrefixMatching         bool `description:"Make prefix matching strictly comply with the Kubernetes Ingress specification (path-element-wise matching instead of character-by-character string matching)." json:"strictPrefixMatching,omitempty" toml:"strictPrefixMatching,omitempty" yaml:"strictPrefixMatching,omitempty" export:"true"`
 
 	// The default rule syntax is initialized with the configuration defined by the user with the core.DefaultRuleSyntax option.
 	DefaultRuleSyntax string `json:"-" toml:"-" yaml:"-" label:"-" file:"-"`
@@ -698,7 +699,7 @@ func (p *Provider) loadRouter(rule netv1.IngressRule, pa netv1.HTTPIngressPath,
 			matcher = "Path"
 		}
 
-		rules = append(rules, fmt.Sprintf("%s(`%s`)", matcher, pa.Path))
+		rules = append(rules, buildRule(p.StrictPrefixMatching, matcher, pa.Path))
 	}
 
 	rt.Rule = strings.Join(rules, " && ")
@@ -844,6 +845,41 @@ func makeRouterKeyWithHash(key, rule string) (string, error) {
 	return dupKey, nil
 }
 
+func buildRule(strictPrefixMatching bool, matcher string, path string) string {
+	// When enabled, strictPrefixMatching ensures that prefix matching follows
+	// the Kubernetes Ingress spec (path-element-wise instead of character-wise).
+	if strictPrefixMatching && matcher == "PathPrefix" {
+		// According to
+		// https://kubernetes.io/docs/concepts/services-networking/ingress/#examples,
+		// "/v12" should not match "/v1".
+		//
+		// Traefik's default PathPrefix matcher performs a character-wise prefix match,
+		// unlike Kubernetes which matches path elements. To mimic Kubernetes behavior,
+		// we will use Path and PathPrefix to replicate element-wise behavior.
+		//
+		// "PathPrefix" in Kubernetes Gateway API is semantically equivalent to the "Prefix" path type in the
+		// Kubernetes Ingress API.
+		return buildStrictPrefixMatchingRule(path)
+	}
+
+	return fmt.Sprintf("%s(`%s`)", matcher, path)
+}
+
+// buildStrictPrefixMatchingRule is a helper function to build a path prefix rule that matches path prefix split by `/`.
+// For example, the paths `/abc`, `/abc/`, and `/abc/def` would all match the prefix `/abc`,
+// but the path `/abcd` would not. See TestStrictPrefixMatchingRule() for more examples.
+//
+// "PathPrefix" in Kubernetes Gateway API is semantically equivalent to the "Prefix" path type in the
+// Kubernetes Ingress API.
+func buildStrictPrefixMatchingRule(path string) string {
+	if path == "/" {
+		return "PathPrefix(`/`)"
+	}
+
+	path = strings.TrimSuffix(path, "/")
+	return fmt.Sprintf("(Path(`%[1]s`) || PathPrefix(`%[1]s/`))", path)
+}
+
 func throttleEvents(ctx context.Context, throttleDuration time.Duration, pool *safe.Pool, eventsChan <-chan interface{}) chan interface{} {
 	if throttleDuration == 0 {
 		return nil

pkg/provider/kubernetes/ingress/kubernetes_test.go

@@ -3,7 +3,10 @@ package ingress
 import (
 	"context"
 	"errors"
+	"fmt"
 	"math"
+	"net/http"
+	"net/http/httptest"
 	"os"
 	"path/filepath"
 	"strings"
@@ -14,6 +17,7 @@ import (
 	"github.com/stretchr/testify/require"
 	ptypes "github.com/traefik/paerser/types"
 	"github.com/traefik/traefik/v3/pkg/config/dynamic"
+	traefikhttp "github.com/traefik/traefik/v3/pkg/muxer/http"
 	"github.com/traefik/traefik/v3/pkg/provider"
 	"github.com/traefik/traefik/v3/pkg/provider/kubernetes/k8s"
 	"github.com/traefik/traefik/v3/pkg/tls"
@@ -38,6 +42,7 @@ func TestLoadConfigurationFromIngresses(t *testing.T) {
 		disableIngressClassLookup    bool
 		disableClusterScopeResources bool
 		defaultRuleSyntax            string
+		strictPrefixMatching         bool
 	}{
 		{
 			desc: "Empty ingresses",
@@ -1621,6 +1626,40 @@ func TestLoadConfigurationFromIngresses(t *testing.T) {
 				},
 			},
 		},
+		{
+			desc: "Ingress with strict prefix matching",
+			expected: &dynamic.Configuration{
+				HTTP: &dynamic.HTTPConfiguration{
+					Middlewares: map[string]*dynamic.Middleware{},
+					Routers: map[string]*dynamic.Router{
+						"testing-bar": {
+							Rule:    "(Path(`/bar`) || PathPrefix(`/bar/`))",
+							Service: "testing-service1-80",
+						},
+					},
+					Services: map[string]*dynamic.Service{
+						"testing-service1-80": {
+							LoadBalancer: &dynamic.ServersLoadBalancer{
+								Strategy:       dynamic.BalancerStrategyWRR,
+								PassHostHeader: pointer(true),
+								ResponseForwarding: &dynamic.ResponseForwarding{
+									FlushInterval: ptypes.Duration(100 * time.Millisecond),
+								},
+								Servers: []dynamic.Server{
+									{
+										URL: "http://10.10.0.1:8080",
+									},
+									{
+										URL: "http://10.21.0.1:8080",
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			strictPrefixMatching: true,
+		},
 	}
 
 	for _, test := range testCases {
@@ -1634,6 +1673,7 @@ func TestLoadConfigurationFromIngresses(t *testing.T) {
 				DisableIngressClassLookup:    test.disableIngressClassLookup,
 				DisableClusterScopeResources: test.disableClusterScopeResources,
 				DefaultRuleSyntax:            test.defaultRuleSyntax,
+				StrictPrefixMatching:         test.strictPrefixMatching,
 			}
 			conf := p.loadConfigurationFromIngresses(context.Background(), clientMock)
 
@@ -2256,3 +2296,106 @@ func readResources(t *testing.T, paths []string) []runtime.Object {
 
 	return k8sObjects
 }
+
+func TestStrictPrefixMatchingRule(t *testing.T) {
+	tests := []struct {
+		path        string
+		requestPath string
+		match       bool
+	}{ // The tests are taken from https://kubernetes.io/docs/concepts/services-networking/ingress/#examples
+		{
+			path:        "/foo",
+			requestPath: "/foo",
+			match:       true,
+		},
+		{
+			path:        "/foo",
+			requestPath: "/foo/",
+			match:       true,
+		},
+		{
+			path:        "/foo/",
+			requestPath: "/foo",
+			match:       true,
+		},
+		{
+			path:        "/foo/",
+			requestPath: "/foo/",
+			match:       true,
+		},
+		{
+			path:        "/aaa/bb",
+			requestPath: "/aaa/bbb",
+			match:       false,
+		},
+		{
+			path:        "/aaa/bbb",
+			requestPath: "/aaa/bbb",
+			match:       true,
+		},
+		{
+			path:        "/aaa/bbb/",
+			requestPath: "/aaa/bbb",
+			match:       true,
+		},
+		{
+			path:        "/aaa/bbb",
+			requestPath: "/aaa/bbb/",
+			match:       true,
+		},
+		{
+			path:        "/aaa/bbb",
+			requestPath: "/aaa/bbb/ccc",
+			match:       true,
+		},
+		{
+			path:        "/aaa/bbb",
+			requestPath: "/aaa/bbbxyz",
+			match:       false,
+		},
+		{
+			path:        "/",
+			requestPath: "/aaa/ccc",
+			match:       true,
+		},
+		{
+			path:        "/aaa",
+			requestPath: "/aaa/ccc",
+			match:       true,
+		},
+		{
+			path:        "/...",
+			requestPath: "/aaa",
+			match:       false,
+		},
+		{
+			path:        "/...",
+			requestPath: "/.../",
+			match:       true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("Prefix match case %s", tt.path), func(t *testing.T) {
+			t.Parallel()
+
+			handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {})
+			muxer, err := traefikhttp.NewMuxer()
+			require.NoError(t, err)
+
+			rule := buildStrictPrefixMatchingRule(tt.path)
+			err = muxer.AddRoute(rule, "", 0, handler)
+			require.NoError(t, err)
+
+			w := httptest.NewRecorder()
+			req := httptest.NewRequest(http.MethodGet, tt.requestPath, http.NoBody)
+			muxer.ServeHTTP(w, req)
+
+			if tt.match {
+				assert.Equal(t, http.StatusOK, w.Code)
+			} else {
+				assert.Equal(t, http.StatusNotFound, w.Code)
+			}
+		})
+	}
+}