Fix panic for ingress with backend resource

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

pkg/provider/kubernetes/ingress/fixtures/Ingress-with-backend-resource.yml

@@ -0,0 +1,18 @@
+kind: Ingress
+apiVersion: networking.k8s.io/v1
+metadata:
+  name: ""
+  namespace: testing
+
+spec:
+  rules:
+  - host: traefik.tchouk
+    http:
+      paths:
+      - path: /bar
+        backend:
+          resource:
+            kind: Service
+            name: service1
+        pathType: Prefix
+

pkg/provider/kubernetes/ingress/fixtures/Ingress-without-backend.yml

@@ -0,0 +1,15 @@
+kind: Ingress
+apiVersion: networking.k8s.io/v1
+metadata:
+  name: ""
+  namespace: testing
+
+spec:
+  rules:
+  - host: traefik.tchouk
+    http:
+      paths:
+      - path: /bar
+        backend: {}
+        pathType: Prefix
+

pkg/provider/kubernetes/ingress/kubernetes.go

@@ -300,6 +300,17 @@ func (p *Provider) loadConfigurationFromIngresses(ctx context.Context, client Cl
 			}
 
 			for _, pa := range rule.HTTP.Paths {
+				if pa.Backend.Resource != nil {
+					// https://kubernetes.io/docs/concepts/services-networking/ingress/#resource-backend
+					log.FromContext(ctxIngress).Error("Resource backends are not supported")
+					continue
+				}
+
+				if pa.Backend.Service == nil {
+					log.FromContext(ctxIngress).Error("Missing service definition")
+					continue
+				}
+
 				service, err := p.loadService(client, ingress.Namespace, pa.Backend)
 				if err != nil {
 					log.FromContext(ctxIngress).
@@ -516,15 +527,6 @@ func getTLSConfig(tlsConfigs map[string]*tls.CertAndStores) []*tls.CertAndStores
 }
 
 func (p *Provider) loadService(client Client, namespace string, backend netv1.IngressBackend) (*dynamic.Service, error) {
-	if backend.Resource != nil {
-		// https://kubernetes.io/docs/concepts/services-networking/ingress/#resource-backend
-		return nil, errors.New("resource backends are not supported")
-	}
-
-	if backend.Service == nil {
-		return nil, errors.New("missing service definition")
-	}
-
 	service, exists, err := client.GetService(namespace, backend.Service.Name)
 	if err != nil {
 		return nil, err

pkg/provider/kubernetes/ingress/kubernetes_test.go

@@ -469,6 +469,30 @@ func TestLoadConfigurationFromIngresses(t *testing.T) {
 				},
 			},
 		},
+		{
+			desc:               "Ingress with backend resource",
+			allowEmptyServices: true,
+			expected: &dynamic.Configuration{
+				TCP: &dynamic.TCPConfiguration{},
+				HTTP: &dynamic.HTTPConfiguration{
+					Middlewares: map[string]*dynamic.Middleware{},
+					Routers:     map[string]*dynamic.Router{},
+					Services:    map[string]*dynamic.Service{},
+				},
+			},
+		},
+		{
+			desc:               "Ingress without backend",
+			allowEmptyServices: true,
+			expected: &dynamic.Configuration{
+				TCP: &dynamic.TCPConfiguration{},
+				HTTP: &dynamic.HTTPConfiguration{
+					Middlewares: map[string]*dynamic.Middleware{},
+					Routers:     map[string]*dynamic.Router{},
+					Services:    map[string]*dynamic.Service{},
+				},
+			},
+		},
 		{
 			desc: "Ingress with one service without endpoint",
 			expected: &dynamic.Configuration{