feat: support kubernetes.io/ingress.class annotations

internal/controller/indexer/indexer.go

@@ -54,6 +54,10 @@ const (
 	ControllerName            = "controllerName"
 )
 
+const (
+	ingressClassNameAnnotation = "kubernetes.io/ingress.class"
+)
+
 func SetupIndexer(mgr ctrl.Manager) error {
 	setupLog := ctrl.LoggerFrom(context.Background()).WithName("indexer-setup")
 
@@ -444,10 +448,15 @@ func IngressClassIndexFunc(rawObj client.Object) []string {
 
 func IngressClassRefIndexFunc(rawObj client.Object) []string {
 	ingress := rawObj.(*networkingv1.Ingress)
-	if ingress.Spec.IngressClassName == nil {
-		return nil
+	if ingress.Spec.IngressClassName != nil && *ingress.Spec.IngressClassName != "" {
+		return []string{*ingress.Spec.IngressClassName}
 	}
-	return []string{*ingress.Spec.IngressClassName}
+	if annotations := ingress.GetAnnotations(); annotations != nil {
+		if className := annotations[ingressClassNameAnnotation]; className != "" {
+			return []string{className}
+		}
+	}
+	return nil
 }
 
 func IngressServiceIndexFunc(rawObj client.Object) []string {

internal/controller/ingress_controller.go

@@ -254,9 +254,19 @@ func (r *IngressReconciler) listIngressForIngressClass(ctx context.Context, obj
 		}
 
 		requests := make([]reconcile.Request, 0, len(ingressList.Items))
-		for _, ingress := range ingressList.Items {
-			if ingress.Spec.IngressClassName == nil || *ingress.Spec.IngressClassName == "" ||
-				*ingress.Spec.IngressClassName == ingressClass.GetName() {
+		for i := range ingressList.Items {
+			ingress := &ingressList.Items[i]
+			specClassName := ptr.Deref(ingress.Spec.IngressClassName, "")
+			annotationClassName := ""
+			if annotations := ingress.GetAnnotations(); annotations != nil {
+				annotationClassName = annotations[ingressClassNameAnnotation]
+			}
+			effectiveClassName := specClassName
+			if effectiveClassName == "" {
+				effectiveClassName = annotationClassName
+			}
+			hasExplicitClass := specClassName != "" || annotationClassName != ""
+			if !hasExplicitClass || effectiveClassName == ingressClass.GetName() {
 				requests = append(requests, reconcile.Request{
 					NamespacedName: client.ObjectKey{
 						Namespace: ingress.Namespace,

internal/controller/utils.go

@@ -82,6 +82,7 @@ const (
 const (
 	defaultIngressClassAnnotation = "ingressclass.kubernetes.io/is-default-class"
 	parametersNamespaceAnnotation = "apisix.apache.org/parameters-namespace"
+	ingressClassNameAnnotation    = "kubernetes.io/ingress.class"
 )
 
 var (
@@ -1718,7 +1719,13 @@ func MatchesIngressClass(c client.Client, log logr.Logger, obj client.Object, ap
 func ExtractIngressClass(obj client.Object) string {
 	switch v := obj.(type) {
 	case *networkingv1.Ingress:
-		return ptr.Deref(v.Spec.IngressClassName, "")
+		if className := ptr.Deref(v.Spec.IngressClassName, ""); className != "" {
+			return className
+		}
+		if annotations := v.GetAnnotations(); annotations != nil {
+			return annotations[ingressClassNameAnnotation]
+		}
+		return ""
 	case *apiv2.ApisixConsumer:
 		return v.Spec.IngressClassName
 	case *apiv2.ApisixRoute:

test/e2e/ingress/ingress.go

@@ -380,6 +380,54 @@ spec:
 		})
 	})
 
+	Context("Ingress Annotation", func() {
+		var ingressSpecWithAnnotation = `
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: %s
+  annotations:
+    kubernetes.io/ingress.class: %s
+spec:
+  rules:
+  - host: annotation.example.com
+    http:
+      paths:
+      - path: /
+        pathType: Prefix
+        backend:
+          service:
+            name: httpbin-service-e2e-test
+            port:
+              number: 80
+`
+
+		It("kubernetes.io/ingress.class", func() {
+			By("create GatewayProxy")
+			err := s.CreateResourceFromString(s.GetGatewayProxySpec())
+			Expect(err).NotTo(HaveOccurred(), "creating GatewayProxy")
+			time.Sleep(5 * time.Second)
+
+			By("create IngressClass")
+			err = s.CreateResourceFromStringWithNamespace(s.GetIngressClassYaml(), s.Namespace())
+			Expect(err).NotTo(HaveOccurred(), "creating GatewayProxy")
+			time.Sleep(5 * time.Second)
+
+			By("create Ingress with annotation-defined class")
+			ingressName := s.Namespace() + "-annotation"
+			err = s.CreateResourceFromString(fmt.Sprintf(ingressSpecWithAnnotation, ingressName, s.Namespace()))
+			Expect(err).NotTo(HaveOccurred(), "creating Ingress with kubernetes.io/ingress.class annotation")
+
+			By("verify ingress served through annotated class")
+			s.RequestAssert(&scaffold.RequestAssert{
+				Method: "GET",
+				Path:   "/get",
+				Host:   "annotation.example.com",
+				Check:  scaffold.WithExpectedStatus(http.StatusOK),
+			})
+		})
+	})
+
 	// Tests concerning the default ingress class need to be run serially
 	Context("IngressClass with GatewayProxy", Serial, func() {
 		gatewayProxyYaml := `