Changes on services must trigger a sync event

internal/ingress/controller/store/store.go

@@ -615,11 +615,27 @@ func New(
 		},
 	}
 
+	serviceHandler := cache.ResourceEventHandlerFuncs{
+		UpdateFunc: func(old, cur interface{}) {
+			oldSvc := old.(*corev1.Service)
+			curSvc := cur.(*corev1.Service)
+
+			if reflect.DeepEqual(oldSvc, curSvc) {
+				return
+			}
+
+			updateCh.In() <- Event{
+				Type: UpdateEvent,
+				Obj:  cur,
+			}
+		},
+	}
+
 	store.informers.Ingress.AddEventHandler(ingEventHandler)
 	store.informers.Endpoint.AddEventHandler(epEventHandler)
 	store.informers.Secret.AddEventHandler(secrEventHandler)
 	store.informers.ConfigMap.AddEventHandler(cmEventHandler)
-	store.informers.Service.AddEventHandler(cache.ResourceEventHandlerFuncs{})
+	store.informers.Service.AddEventHandler(serviceHandler)
 	store.informers.Pod.AddEventHandler(podEventHandler)
 
 	// do not wait for informers to read the configmap configuration

test/e2e/servicebackend/service_externalname.go

@@ -17,15 +17,20 @@ limitations under the License.
 package servicebackend
 
 import (
+	"context"
+	"fmt"
 	"net/http"
 	"strings"
+	"time"
 
 	"github.com/onsi/ginkgo"
+	"github.com/stretchr/testify/assert"
 	core "k8s.io/api/core/v1"
 	corev1 "k8s.io/api/core/v1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	"k8s.io/apimachinery/pkg/util/intstr"
 
+	"k8s.io/ingress-nginx/internal/nginx"
 	"k8s.io/ingress-nginx/test/e2e/framework"
 )
 
@@ -203,4 +208,73 @@ var _ = framework.IngressNginxDescribe("[Service] Type ExternalName", func() {
 			Expect().
 			Status(http.StatusOK)
 	})
+
+	ginkgo.It("should update the external name after a service update", func() {
+		host := "echo"
+
+		svc := &core.Service{
+			ObjectMeta: metav1.ObjectMeta{
+				Name:      framework.HTTPBinService,
+				Namespace: f.Namespace,
+			},
+			Spec: corev1.ServiceSpec{
+				ExternalName: "httpbin.org",
+				Type:         corev1.ServiceTypeExternalName,
+				Ports: []corev1.ServicePort{
+					{
+						Name:       host,
+						Port:       80,
+						TargetPort: intstr.FromInt(80),
+						Protocol:   "TCP",
+					},
+				},
+			},
+		}
+		f.EnsureService(svc)
+
+		ing := framework.NewSingleIngress(host, "/", host, f.Namespace, framework.HTTPBinService, 80, nil)
+		ing.Spec.Rules[0].HTTP.Paths[0].Backend.ServicePort = intstr.FromString(host)
+		f.EnsureIngress(ing)
+
+		f.WaitForNginxServer(host,
+			func(server string) bool {
+				return strings.Contains(server, "proxy_pass http://upstream_balancer;")
+			})
+
+		body := f.HTTPTestClient().
+			GET("/get").
+			WithHeader("Host", host).
+			Expect().
+			Status(http.StatusOK).
+			Body().
+			Raw()
+
+		assert.Contains(ginkgo.GinkgoT(), body, `"X-Forwarded-Host": "echo"`)
+
+		svc, err := f.KubeClientSet.CoreV1().Services(f.Namespace).Get(context.TODO(), framework.HTTPBinService, metav1.GetOptions{})
+		assert.Nil(ginkgo.GinkgoT(), err, "unexpected error obtaining httpbin service")
+
+		svc.Spec.ExternalName = "eu.httpbin.org"
+
+		_, err = f.KubeClientSet.CoreV1().Services(f.Namespace).Update(context.Background(), svc, metav1.UpdateOptions{})
+		assert.Nil(ginkgo.GinkgoT(), err, "unexpected error updating httpbin service")
+
+		time.Sleep(5 * time.Second)
+
+		body = f.HTTPTestClient().
+			GET("/get").
+			WithHeader("Host", host).
+			Expect().
+			Status(http.StatusOK).
+			Body().
+			Raw()
+
+		assert.Contains(ginkgo.GinkgoT(), body, `"X-Forwarded-Host": "echo"`)
+
+		ginkgo.By("checking the service is updated to use eu.httpbin.org")
+		curlCmd := fmt.Sprintf("curl --fail --silent http://localhost:%v/configuration/backends", nginx.StatusPort)
+		output, err := f.ExecIngressPod(curlCmd)
+		assert.Nil(ginkgo.GinkgoT(), err)
+		assert.Contains(ginkgo.GinkgoT(), output, `{"address":"eu.httpbin.org"`)
+	})
 })