feature: forward backend for ingress as annotation zalando.org/skipper-backend (#3665)

feature: [forward
backend](https://opensource.zalando.com/skipper/reference/backends/#forward-backend)
for ingress as annotation `zalando.org/skipper-backend`.

RouteGroup validation makes sure that the backend type is recognized.
dataclients/kubernetes/definitions/testdata/validation/test-forward.log
is an empty file, because if log file does not exist test would be
skipped.

Signed-off-by: Sandor Szücs <[email protected]>

Author: szuecs

dataclients/kubernetes/definitions/ingressv1.go

@@ -10,6 +10,7 @@ const (
 	IngressFilterAnnotation    = "zalando.org/skipper-filter"
 	IngressPredicateAnnotation = "zalando.org/skipper-predicate"
 	IngressRoutesAnnotation    = "zalando.org/skipper-routes"
+	IngressBackendAnnotation   = "zalando.org/skipper-backend"
 )
 
 var errInvalidPortType = errors.New("invalid port type")

dataclients/kubernetes/definitions/testdata/validation/test-forward.log

@@ -0,0 +1,12 @@
+apiVersion: zalando.org/v1
+kind: RouteGroup
+metadata:
+  name: my-test
+spec:
+  backends:
+  - name: fwd
+    type: forward
+  routes:
+    - pathSubtree: /
+      backends:
+        - backendName: fwd

dataclients/kubernetes/definitions/testdata/validation/test-forward.yaml

@@ -35,6 +35,8 @@ type ingressContext struct {
 	logger              *logger
 	annotationFilters   []*eskip.Filter
 	annotationPredicate string
+	annotationBackend   string
+	forwardBackendURL   string
 	extraRoutes         []*eskip.Route
 	backendWeights      map[string]float64
 	pathMode            PathMode
@@ -58,6 +60,7 @@ type ingress struct {
 	forceKubernetesService                         bool
 	backendTrafficAlgorithm                        BackendTrafficAlgorithm
 	defaultLoadBalancerAlgorithm                   string
+	forwardBackendURL                              string
 	kubernetesAnnotationPredicates                 []AnnotationPredicates
 	kubernetesAnnotationFiltersAppend              []AnnotationFilters
 	kubernetesEastWestRangeAnnotationPredicates    []AnnotationPredicates
@@ -69,9 +72,26 @@ var nonWord = regexp.MustCompile(`\W`)
 var errNotAllowedExternalName = errors.New("ingress with not allowed external name service")
 
 func (ic *ingressContext) addHostRoute(host string, route *eskip.Route) {
+	ic.applyBackend(route)
 	ic.hostRoutes[host] = append(ic.hostRoutes[host], route)
 }
 
+func (ic *ingressContext) applyBackend(route *eskip.Route) {
+	if ic.forwardBackendURL == "" || ic.annotationBackend == "" || route == nil {
+		return
+	}
+	if be, err := eskip.BackendTypeFromString(ic.annotationBackend); err != nil {
+		return
+	} else {
+		switch be {
+		case eskip.ForwardBackend:
+			route.BackendType = eskip.NetworkBackend
+			route.Backend = ic.forwardBackendURL
+			route.Filters = []*eskip.Filter{}
+		}
+	}
+}
+
 func newIngress(o Options) *ingress {
 	return &ingress{
 		provideHTTPSRedirect:                           o.ProvideHTTPSRedirect,
@@ -86,6 +106,7 @@ func newIngress(o Options) *ingress {
 		forceKubernetesService:                         o.ForceKubernetesService,
 		backendTrafficAlgorithm:                        o.BackendTrafficAlgorithm,
 		defaultLoadBalancerAlgorithm:                   o.DefaultLoadBalancerAlgorithm,
+		forwardBackendURL:                              o.ForwardBackendURL,
 		kubernetesAnnotationPredicates:                 o.KubernetesAnnotationPredicates,
 		kubernetesAnnotationFiltersAppend:              o.KubernetesAnnotationFiltersAppend,
 		kubernetesEastWestRangeAnnotationPredicates:    o.KubernetesEastWestRangeAnnotationPredicates,
@@ -262,6 +283,21 @@ func annotationFilter(m *definitions.Metadata, logger *logger) []*eskip.Filter {
 	return nil
 }
 
+// parse backend annotation
+func annotationBackend(m *definitions.Metadata) (eskip.BackendType, error) {
+	if s, ok := m.Annotations[definitions.IngressBackendAnnotation]; ok {
+		return eskip.BackendTypeFromString(s)
+	}
+	return 0, fmt.Errorf("annotation not found")
+}
+
+func annotationBackendString(m *definitions.Metadata) string {
+	if be, err := annotationBackend(m); err == nil {
+		return be.String()
+	}
+	return ""
+}
+
 // parse predicate annotation
 func annotationPredicate(m *definitions.Metadata) string {
 	var annotationPredicate string
@@ -350,6 +386,22 @@ func hasCatchAllRoutes(routes []*eskip.Route) bool {
 	return false
 }
 
+func (ing *ingress) applyBackend(i *definitions.IngressV1Item, r *eskip.Route) {
+	if ing.forwardBackendURL == "" || r == nil {
+		return
+	}
+	if be, err := annotationBackend(i.Metadata); err != nil {
+		return
+	} else {
+		switch be {
+		case eskip.ForwardBackend:
+			r.BackendType = eskip.NetworkBackend
+			r.Backend = ing.forwardBackendURL
+			r.Filters = []*eskip.Filter{}
+		}
+	}
+}
+
 // convert logs if an invalid found, but proceeds with the valid ones.
 // Reporting failures in Ingress status is not possible, because
 // Ingress status field only supports IP and Hostname as string.
@@ -372,6 +424,7 @@ func (ing *ingress) convert(state *clusterState, df defaultFilters, r *certregis
 				ewIngInfo[r.Id] = []string{i.Metadata.Namespace, i.Metadata.Name}
 			}
 		}
+		ing.applyBackend(i, r)
 	}
 
 	for host, rs := range hostRoutes {

dataclients/kubernetes/ingress.go

@@ -27,5 +27,6 @@ func TestIngressV1AnnotationConfig(t *testing.T) {
 	kubernetestest.FixturesToTest(t,
 		"testdata/ingressV1/annotation-predicates",
 		"testdata/ingressV1/annotation-filters",
+		"testdata/ingressV1/annotation-backends",
 	)
 }

dataclients/kubernetes/ingress_test.go

@@ -433,6 +433,8 @@ func (ing *ingress) ingressV1Route(
 		logger:              logger,
 		annotationFilters:   annotationFilter(i.Metadata, logger),
 		annotationPredicate: annotationPredicate(i.Metadata),
+		annotationBackend:   annotationBackendString(i.Metadata),
+		forwardBackendURL:   ing.forwardBackendURL,
 		extraRoutes:         extraRoutes(i.Metadata),
 		backendWeights:      backendWeights(i.Metadata, logger),
 		pathMode:            pathMode(i.Metadata, ing.pathMode, logger),
@@ -446,9 +448,11 @@ func (ing *ingress) ingressV1Route(
 	var route *eskip.Route
 	if r, ok, err := ing.convertDefaultBackendV1(ic, ing.forceKubernetesService); ok {
 		route = r
+		ic.applyBackend(route)
 	} else if err != nil {
 		ic.logger.Errorf("Failed to convert default backend: %v", err)
 	}
+
 	for _, rule := range i.Spec.Rules {
 		err := ing.addSpecRuleV1(ic, rule)
 		if err != nil {

dataclients/kubernetes/ingressv1.go

@@ -0,0 +1,6 @@
+kube_default__myapp__example_test____myapp:
+	Host("^(example[.]test[.]?(:[0-9]+)?)$")
+	-> "http://forward.example";
+
+kube_default__myapp__0__example_test____: Host("^(example[.]test[.]?(:[0-9]+)?)$") && Method("OPTIONS") -> <shunt>;
+

dataclients/kubernetes/testdata/ingressV1/annotation-backends/forward-custom-route.eskip

@@ -0,0 +1,52 @@
+apiVersion: networking.k8s.io/v1
+kind: Ingress
+metadata:
+  name: myapp
+  namespace: default
+  annotations:
+    zalando.org/skipper-backend: forward
+    zalando.org/skipper-routes: Method("OPTIONS") -> status(200) -> <shunt>
+spec:
+  rules:
+  - host: example.test
+    http:
+      paths:
+      - backend:
+          service:
+            name: myapp
+            port:
+              number: 80
+        pathType: ImplementationSpecific
+---
+apiVersion: v1
+kind: Service
+metadata:
+  labels:
+    application: myapp
+  name: myapp
+spec:
+  clusterIP: 10.3.190.97
+  ports:
+  - name: main
+    port: 80
+    protocol: TCP
+    targetPort: 7272
+  selector:
+    application: myapp
+  type: ClusterIP
+---
+apiVersion: v1
+kind: Endpoints
+metadata:
+  labels:
+    application: myapp
+  name: myapp
+  namespace: default
+subsets:
+- addresses:
+  - ip: 10.2.9.103
+  - ip: 10.2.9.104
+  ports:
+  - name: main
+    port: 7272
+    protocol: TCP

dataclients/kubernetes/testdata/routegroups/backends/forward.kube renamed to dataclients/kubernetes/testdata/ingressV1/annotation-backends/forward-custom-route.kube

@@ -0,0 +1,3 @@
+kube_default__myapp__example_test____myapp:
+	Host("^(example[.]test[.]?(:[0-9]+)?)$")
+	-> "http://forward.example";