Allow the usage of Services as Upstream on a global level (#7469)

It is possible to change this behavior on an ingress level, which works
well when you only have a few of them. When running several dozen
ingress and with a high change rate of running pods it makes it easier
to define this configuration on a global level.

This change is completely backwards compatible, only adding the
possibility of defining a new key in the configmap.

test/e2e/annotations/serviceupstream.go

@@ -0,0 +1,128 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package annotations
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+
+	"github.com/onsi/ginkgo"
+	"github.com/stretchr/testify/assert"
+
+	"k8s.io/ingress-nginx/test/e2e/framework"
+
+	"k8s.io/ingress-nginx/internal/nginx"
+)
+
+var _ = framework.DescribeAnnotation("service-upstream", func() {
+	f := framework.NewDefaultFramework("serviceupstream")
+	host := "serviceupstream"
+
+	ginkgo.BeforeEach(func() {
+		f.NewEchoDeployment()
+	})
+
+	ginkgo.Context("when using the default value (false) and enabling in the annotations", func() {
+		ginkgo.It("should use the Service Cluster IP and Port ", func() {
+			annotations := map[string]string{
+				"nginx.ingress.kubernetes.io/service-upstream": "true",
+			}
+
+			ing := framework.NewSingleIngress(host, "/", host, f.Namespace, framework.EchoService, 80, annotations)
+			f.EnsureIngress(ing)
+
+			f.WaitForNginxServer(host, func(server string) bool {
+				return strings.Contains(server, fmt.Sprintf("server_name %s", host))
+			})
+
+			ginkgo.By("checking if the service is reached")
+			f.HTTPTestClient().
+				GET("/").
+				WithHeader("Host", host).
+				Expect().
+				Status(http.StatusOK)
+
+			ginkgo.By("checking if the Service Cluster IP and Port are used")
+			s := f.GetService(f.Namespace, framework.EchoService)
+			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, fmt.Sprintf(`{"address":"%s"`, s.Spec.ClusterIP))
+		})
+	})
+
+	ginkgo.Context("when enabling in the configmap", func() {
+		ginkgo.It("should use the Service Cluster IP and Port ", func() {
+			annotations := map[string]string{}
+
+			f.UpdateNginxConfigMapData("service-upstream", "true")
+
+			ing := framework.NewSingleIngress(host, "/", host, f.Namespace, framework.EchoService, 80, annotations)
+			f.EnsureIngress(ing)
+
+			f.WaitForNginxServer(host, func(server string) bool {
+				return strings.Contains(server, fmt.Sprintf("server_name %s", host))
+			})
+
+			ginkgo.By("checking if the service is reached")
+			f.HTTPTestClient().
+				GET("/").
+				WithHeader("Host", host).
+				Expect().
+				Status(http.StatusOK)
+
+			ginkgo.By("checking if the Service Cluster IP and Port are used")
+			s := f.GetService(f.Namespace, framework.EchoService)
+			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, fmt.Sprintf(`{"address":"%s"`, s.Spec.ClusterIP))
+		})
+	})
+
+	ginkgo.Context("when enabling in the configmap and disabling in the annotations", func() {
+		ginkgo.It("should not use the Service Cluster IP and Port", func() {
+			annotations := map[string]string{
+				"nginx.ingress.kubernetes.io/service-upstream": "false",
+			}
+
+			f.UpdateNginxConfigMapData("service-upstream", "true")
+
+			ing := framework.NewSingleIngress(host, "/", host, f.Namespace, framework.EchoService, 80, annotations)
+			f.EnsureIngress(ing)
+
+			f.WaitForNginxServer(host, func(server string) bool {
+				return strings.Contains(server, fmt.Sprintf("server_name %s", host))
+			})
+
+			ginkgo.By("checking if the service is reached")
+			f.HTTPTestClient().
+				GET("/").
+				WithHeader("Host", host).
+				Expect().
+				Status(http.StatusOK)
+
+			ginkgo.By("checking if the Service Cluster IP and Port are not used")
+			s := f.GetService(f.Namespace, framework.EchoService)
+			curlCmd := fmt.Sprintf("curl --fail --silent http://localhost:%v/configuration/backends", nginx.StatusPort)
+			output, err := f.ExecIngressPod(curlCmd)
+			assert.Nil(ginkgo.GinkgoT(), err)
+			assert.NotContains(ginkgo.GinkgoT(), output, fmt.Sprintf(`{"address":"%s"`, s.Spec.ClusterIP))
+		})
+	})
+})