[WIP] Make (cluster-local) DNS work out of the box by default.

config/config-domain.yaml

@@ -19,12 +19,15 @@ metadata:
   namespace: knative-serving
 data:
   # These are example settings of domain.
-  # example.org will be used for routes having app=prod.
-  # example.org: |
+  # example.com will be used for routes having app=external.
+  # example.com: |
   #   selector:
-  #     app: prod
+  #     app: external
 
-  # Default value for domain, for routes that does not have app=prod labels.
-  # Although it will match all routes, it is the least-specific rule so it
-  # will only be used if no other domain matches.
-  example.com: |
+  # This is the default value for domain, for routes that does not have
+  # app=external labels. This is the least-specific rule and acts as a default.
+  # The 'svc.cluster.local' default provides a DNS name which works inside the
+  # cluster. If you want your cluster to be public, you'll need to follow the
+  # instructions here:
+  # https://github.com/knative/docs/blob/master/serving/using-a-custom-domain.md#publish-your-domain
+  svc.cluster.local: |

pkg/controller/route/resources/service.go

@@ -39,10 +39,8 @@ func MakeK8sService(route *v1alpha1.Route) *corev1.Service {
 			},
 		},
 		Spec: corev1.ServiceSpec{
-			Ports: []corev1.ServicePort{{
-				Name: PortName,
-				Port: PortNumber,
-			}},
+			Type:         corev1.ServiceTypeExternalName,
+			ExternalName: "knative-ingressgateway.istio-system.svc.cluster.local",
 		},
 	}
 }

pkg/controller/route/resources/virtual_service.go

@@ -80,10 +80,12 @@ func makeVirtualServiceSpec(u *v1alpha1.Route, targets map[string][]traffic.Revi
 			// Traffic originates from outside of the cluster would be of the form "*.domain", or "domain"
 			fmt.Sprintf("*.%s", domain),
 			domain,
-			// Traffic from inside the cluster will use the FQDN of the Route's headless Service.
-			names.K8sServiceFullname(u),
 		},
 	}
+	if domain != names.K8sServiceFullname(u) {
+		// Add a local alias for the k8s Service in the svc.cluster.local DNS space.
+		spec.Hosts = append(spec.Hosts, names.K8sServiceFullname(u))
+	}
 	names := []string{}
 	for name := range targets {
 		names = append(names, name)