Merge pull request #801 from gigi-at-zymergen/797

#797 Add a forward actions annotation to allow forwarding to external target groups

Author: k8s-ci-robot

docs/guide/tasks/migrate_legacy_apps.md

@@ -0,0 +1,42 @@
+# Migrating From Legacy Apps with Manually Configured Target Groups
+
+Many organizations are decomposing old legacy apps into smaller services and components. 
+
+During the transition they may be running a hybrid ecosystem with some parts of the app running in ec2 instances, 
+some in Kubernetes microservices, and possibly even some in serverless environments like Lambda. 
+
+The existing clients of the application expect all endpoints under one DNS entry and it's desirable to be able
+to route traffic at the ALB to services running outside the Kubernetes cluster. 
+
+The actions annotation allows the definition of a forward rule to a previously configured target group. 
+Learn more about the actions annotation at
+[`alb.ingress.kubernetes.io/actions.${action-name}`](../ingress/annotation.md#actions)
+
+## Example Ingress Manifest
+```yaml
+apiVersion: extensions/v1beta1
+kind: Ingress
+metadata:
+  namespace: testcase
+  name: echoserver
+  annotations:
+    kubernetes.io/ingress.class: alb
+    alb.ingress.kubernetes.io/actions.legacy-app: '{"Type": "forward", "TargetGroupArn": "legacy-tg-arn"}'
+spec:
+  rules:
+    - http:
+        paths:
+          - path: /v1/endpoints
+            backend:
+              serviceName: legacy-app
+              servicePort: use-annotation
+          - path: /normal-path
+            backend:
+              serviceName: echoserver
+              servicePort: 80
+```
+
+!!!note
+    The `TargetGroupArn` must be set and the user is responsible for configuring the Target group in AWS before applying
+    the forward rule.    
+

internal/ingress/annotations/action/main.go

@@ -61,6 +61,10 @@ func (a action) Parse(ing parser.AnnotationInterface) (interface{}, error) {
 			if data.RedirectConfig == nil {
 				return nil, fmt.Errorf("%v is type redirect but did not include a valid RedirectConfig configuration", serviceName)
 			}
+		case "forward":
+			if data.TargetGroupArn == nil {
+				return nil, fmt.Errorf("%v is type forward but did not include a valid TargetGroupArn configuration", serviceName)
+			}
 		default:
 			return nil, fmt.Errorf("an invalid action type %v was configured in %v", *data.Type, serviceName)
 		}
@@ -158,6 +162,10 @@ func Dummy() *Config {
 					MessageBody: aws.String("message body"),
 				},
 			}),
+			"forward": setDefaults(&elbv2.Action{
+				Type:           aws.String(elbv2.ActionTypeEnumForward),
+				TargetGroupArn: aws.String("legacy-tg-arn"),
+			}),
 		},
 	}
 }

internal/ingress/annotations/action/main_test.go

@@ -22,6 +22,7 @@ func TestIngressActions(t *testing.T) {
 	"StatusCode":"503", "MessageBody":"message body"}}`
 	data[parser.GetAnnotationWithPrefix("actions.redirect-action")] = `{"Type": "redirect", "RedirectConfig": {"Protocol":"HTTPS",
   "Port":"443", "Host":"#{host}", "Path": "/#{path}", "Query": "#{query}", "StatusCode": "HTTP_301"}}`
+	data[parser.GetAnnotationWithPrefix("actions.forward")] = `{"Type": "forward", "TargetGroupArn": "legacy-tg-arn"}`
 	ing.SetAnnotations(data)
 
 	ai, err := NewParser(mockBackend{}).Parse(ing)