Fix default-backend annotation

internal/ingress/annotations/annotations.go

@@ -21,6 +21,7 @@ import (
 	"github.com/imdario/mergo"
 	"k8s.io/ingress-nginx/internal/ingress/annotations/sslcipher"
 
+	apiv1 "k8s.io/api/core/v1"
 	extensions "k8s.io/api/extensions/v1beta1"
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
@@ -72,7 +73,7 @@ type Ingress struct {
 	ConfigurationSnippet string
 	Connection           connection.Config
 	CorsConfig           cors.Config
-	DefaultBackend       string
+	DefaultBackend       *apiv1.Service
 	Denied               error
 	ExternalAuth         authreq.Config
 	HealthCheck          healthcheck.Config

internal/ingress/controller/controller.go

@@ -451,6 +451,7 @@ func (n *NGINXController) getBackendServers(ingresses []*extensions.Ingress) ([]
 						loc.GRPC = anns.GRPC
 						loc.LuaRestyWAF = anns.LuaRestyWAF
 						loc.InfluxDB = anns.InfluxDB
+						loc.DefaultBackend = anns.DefaultBackend
 
 						if loc.Redirect.FromToWWW {
 							server.RedirectFromToWWW = true
@@ -488,6 +489,7 @@ func (n *NGINXController) getBackendServers(ingresses []*extensions.Ingress) ([]
 						GRPC:                 anns.GRPC,
 						LuaRestyWAF:          anns.LuaRestyWAF,
 						InfluxDB:             anns.InfluxDB,
+						DefaultBackend:       anns.DefaultBackend,
 					}
 
 					if loc.Redirect.FromToWWW {

test/e2e/annotations/default_backend.go

@@ -0,0 +1,58 @@
+/*
+Copyright 2018 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"
+	"time"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+
+	"k8s.io/ingress-nginx/test/e2e/framework"
+)
+
+var _ = framework.IngressNginxDescribe("Annotations - custom default-backend", func() {
+	f := framework.NewDefaultFramework("default-backend")
+
+	BeforeEach(func() {
+		err := f.NewEchoDeployment()
+		Expect(err).NotTo(HaveOccurred())
+	})
+
+	Context("when default backend annotation is enabled", func() {
+		It("should use a custom default backend as upstream", func() {
+			host := "default-backend"
+
+			annotations := map[string]string{
+				"nginx.ingress.kubernetes.io/default-backend": "http-svc",
+			}
+			ing, err := f.EnsureIngress(framework.NewSingleIngress(host, "/", host, f.IngressController.Namespace, "invalid", 80, &annotations))
+			Expect(err).NotTo(HaveOccurred())
+			Expect(ing).NotTo(BeNil())
+
+			time.Sleep(5 * time.Second)
+
+			err = f.WaitForNginxServer(host,
+				func(server string) bool {
+					return Expect(server).Should(ContainSubstring(fmt.Sprintf("server_name %v", host))) &&
+						Expect(server).Should(ContainSubstring("proxy_pass http://custom-default-backend"))
+				})
+			Expect(err).NotTo(HaveOccurred())
+		})
+	})
+})