feat: support dual stack for gateway api

docs/sources/gateway.md

@@ -5,7 +5,7 @@ sources create DNS entries based on their respective `gateway.networking.k8s.io`
 
 ## Filtering the Routes considered
 
-These sources support the `--label-filter` flag, which filters *Route resources
+These sources support the `--label-filter` flag, which filters \*Route resources
 by a set of labels.
 
 ## Domain names
@@ -16,67 +16,103 @@ of [domain names from the *Route](#domain-names-from-route).
 It then iterates over each of the `status.parents` with
 a [matching Gateway](#matching-gateways) and at least one [matching listener](#matching-listeners).
 For each matching listener, if the
-listener has a `hostname`, it narrows the set of domain names from the *Route to the portion
+listener has a `hostname`, it narrows the set of domain names from the \*Route to the portion
 that overlaps the `hostname`. If a matching listener does not have a `hostname`, it uses
 the un-narrowed set of domain names.
 
 ### Domain names from Route
 
-The set of domain names from a *Route is sourced from the following places:
+The set of domain names from a \*Route is sourced from the following places:
 
-* If the *Route is a GRPCRoute, HTTPRoute, or TLSRoute, adds each of the`spec.hostnames`.
+- If the \*Route is a GRPCRoute, HTTPRoute, or TLSRoute, adds each of the`spec.hostnames`.
 
-* Adds the hostnames from any `external-dns.alpha.kubernetes.io/hostname` annotation on the *Route.
-This behavior is suppressed if the `--ignore-hostname-annotation` flag was specified.
+- Adds the hostnames from any `external-dns.alpha.kubernetes.io/hostname` annotation on the \*Route.
+  This behavior is suppressed if the `--ignore-hostname-annotation` flag was specified.
 
-* If no endpoints were produced by the previous steps
-or the `--combine-fqdn-annotation` flag was specified, then adds hostnames
-generated from any`--fqdn-template` flag.
+- If no endpoints were produced by the previous steps
+  or the `--combine-fqdn-annotation` flag was specified, then adds hostnames
+  generated from any`--fqdn-template` flag.
 
-* If no endpoints were produced by the previous steps, each
-attached Gateway listener will use its `hostname`, if present.
+- If no endpoints were produced by the previous steps, each
+  attached Gateway listener will use its `hostname`, if present.
 
 ### Matching Gateways
 
-Matching Gateways are discovered by iterating over the *Route's `status.parents`:
+Matching Gateways are discovered by iterating over the \*Route's `status.parents`:
 
-* Ignores parents with a `parentRef.group` other than
-`gateway.networking.k8s.io` or a `parentRef.kind` other than `Gateway`.
+- Ignores parents with a `parentRef.group` other than
+  `gateway.networking.k8s.io` or a `parentRef.kind` other than `Gateway`.
 
-* If the `--gateway-namespace` flag was specified, ignores parents with a `parentRef.namespace` other
-than the specified value.
+- If the `--gateway-namespace` flag was specified, ignores parents with a `parentRef.namespace` other
+  than the specified value.
 
-* If the `--gateway-label-filter` flag was specified, ignores parents whose Gateway does not match the
-specified label filter.
+- If the `--gateway-label-filter` flag was specified, ignores parents whose Gateway does not match the
+  specified label filter.
 
-* Ignores parents whose Gateway either does not exist or has not accepted the route.
+- Ignores parents whose Gateway either does not exist or has not accepted the route.
 
 ### Matching listeners
 
 Iterates over all listeners for the parent's `parentRef.sectionName`:
 
-* Ignores listeners whose `protocol` field does not match the kind of the *Route per the following table:
+- Ignores listeners whose `protocol` field does not match the kind of the \*Route per the following table:
 
-| kind       | protocols   |
-|------------|-------------|
-| GRPCRoute  | HTTP, HTTPS |
-| HTTPRoute  | HTTP, HTTPS |
-| TCPRoute   | TCP         |
-| TLSRoute   | TLS         |
-| UDPRoute   | UDP         |
+| kind      | protocols   |
+| --------- | ----------- |
+| GRPCRoute | HTTP, HTTPS |
+| HTTPRoute | HTTP, HTTPS |
+| TCPRoute  | TCP         |
+| TLSRoute  | TLS         |
+| UDPRoute  | UDP         |
 
-* If the parent's `parentRef.port` port is specified, ignores listeners without a matching `port`.
+- If the parent's `parentRef.port` port is specified, ignores listeners without a matching `port`.
 
-* Ignores listeners which specify an `allowedRoutes` which does not allow the route.
+- Ignores listeners which specify an `allowedRoutes` which does not allow the route.
 
 ## Targets
 
-The targets of the DNS entries created from a *Route are sourced from the following places:
-
-1. If a matching parent Gateway has an `external-dns.alpha.kubernetes.io/target` annotation, uses 
-the values from that. 
-
-2. Otherwise, iterates over that parent Gateway's `status.addresses`, 
-adding each address's `value`. 
-
-The targets from each parent Gateway matching the *Route are then combined and de-duplicated.
+The targets of the DNS entries created from a \*Route are sourced from the following places:
+
+1. If a matching parent Gateway has an `external-dns.alpha.kubernetes.io/target` annotation, uses
+   the values from that.
+
+2. Otherwise, iterates over that parent Gateway's `status.addresses`,
+   adding each address's `value`.
+
+The targets from each parent Gateway matching the \*Route are then combined and de-duplicated.
+
+## Dualstack Routes
+
+Gateway resources may be served from an external-loadbalancer which may support both IPv4 and "dualstack" (both IPv4 and IPv6) interfaces.
+External DNS Controller uses the `external-dns.alpha.kubernetes.io/dualstack` annotation to determine this. If this annotation is
+set to `true` then ExternalDNS will create two records (one A record
+and one AAAA record) for each hostname associated with the Route resource.
+
+Example:
+
+```yaml
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  annotations:
+    external-dns.alpha.kubernetes.io/dualstack: "true"
+  name: echo
+spec:
+  hostnames:
+    - echoserver.example.org
+  rules:
+    - backendRefs:
+        - group: ""
+          kind: Service
+          name: echo
+          port: 1027
+          weight: 1
+      matches:
+        - path:
+            type: PathPrefix
+            value: /echo
+```
+
+The above HTTPRoute resource is backed by a dualstack Gateway.
+ExternalDNS will create both an A `echoserver.example.org` record and
+an AAAA record of the same name, that each are aliases for the same LB.

source/gateway.go

@@ -44,6 +44,10 @@ import (
 const (
 	gatewayGroup = "gateway.networking.k8s.io"
 	gatewayKind  = "Gateway"
+	// gatewayAPIDualstackAnnotationKey is the annotation used for determining if a Gateway Route is dualstack
+	gatewayAPIDualstackAnnotationKey = "external-dns.alpha.kubernetes.io/dualstack"
+	// gatewayAPIDualstackAnnotationValue is the value of the Gateway Route dualstack annotation that indicates it is dualstack
+	gatewayAPIDualstackAnnotationValue = "true"
 )
 
 type gatewayRoute interface {
@@ -235,6 +239,7 @@ func (src *gatewayRouteSource) Endpoints(ctx context.Context) ([]*endpoint.Endpo
 		for host, targets := range hostTargets {
 			endpoints = append(endpoints, endpointsForHostname(host, targets, ttl, providerSpecific, setIdentifier, resource)...)
 		}
+		setDualstackLabel(rt, endpoints)
 		log.Debugf("Endpoints generated from %s %s/%s: %v", src.rtKind, meta.Namespace, meta.Name, endpoints)
 	}
 	return endpoints, nil
@@ -609,3 +614,13 @@ func selectorsEqual(a, b labels.Selector) bool {
 	}
 	return true
 }
+
+func setDualstackLabel(rt gatewayRoute, endpoints []*endpoint.Endpoint) {
+	val, ok := rt.Metadata().Annotations[gatewayAPIDualstackAnnotationKey]
+	if ok && val == gatewayAPIDualstackAnnotationValue {
+		log.Debugf("Adding dualstack label to GatewayRoute %s/%s.", rt.Metadata().Namespace, rt.Metadata().Name)
+		for _, ep := range endpoints {
+			ep.Labels[endpoint.DualstackLabelKey] = "true"
+		}
+	}
+}

source/gateway_test.go

@@ -20,6 +20,7 @@ import (
 	"strings"
 	"testing"
 
+	"sigs.k8s.io/external-dns/endpoint"
 	v1 "sigs.k8s.io/gateway-api/apis/v1"
 )
 
@@ -245,3 +246,47 @@ func TestIsDNS1123Domain(t *testing.T) {
 		})
 	}
 }
+
+func TestDualStackLabel(t *testing.T) {
+	tests := []struct {
+		desc      string
+		in        map[string](string)
+		setsLabel bool
+	}{
+		{
+			desc:      "empty-annotation",
+			setsLabel: false,
+		},
+		{
+			desc:      "correct-annotation-key-and-value",
+			in:        map[string]string{gatewayAPIDualstackAnnotationKey: gatewayAPIDualstackAnnotationValue},
+			setsLabel: true,
+		},
+		{
+			desc:      "correct-annotation-key-incorrect-value",
+			in:        map[string]string{gatewayAPIDualstackAnnotationKey: "foo"},
+			setsLabel: false,
+		},
+		{
+			desc:      "incorrect-annotation-key-correct-value",
+			in:        map[string]string{"FOO": gatewayAPIDualstackAnnotationValue},
+			setsLabel: false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			endpoints := make([]*endpoint.Endpoint, 0)
+			endpoints = append(endpoints, endpoint.NewEndpoint("www.example.com", endpoint.RecordTypeA, "10.0.0.2", "10.0.0.3"))
+
+			rt := &gatewayHTTPRoute{}
+			rt.Metadata().Annotations = tt.in
+
+			setDualstackLabel(rt, endpoints)
+			got := endpoints[0].Labels[endpoint.DualstackLabelKey] == "true"
+
+			if got != tt.setsLabel {
+				t.Errorf("setDualstackLabel(%q); got: %v; want: %v", tt.in, got, tt.setsLabel)
+			}
+		})
+	}
+}