feat: add support for aws dualstack nlbs

docs/tutorials/aws-load-balancer-controller.md

@@ -176,3 +176,37 @@ spec:
 The above Ingress object will result in the creation of an ALB with a dualstack
 interface. 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 ALB.
+
+## Dualstack NLBs
+
+AWS supports both IPv4 and "dualstack" (both IPv4 and IPv6) interfaces for NLBs.
+The AWS Load Balancer Controller uses the `service.beta.kubernetes.io/aws-load-balancer-ip-address-type`
+[annotation][5] (which defaults to `ipv4`) to determine this. When this annotation is
+set to `dualstack`, ExternalDNS create two alias records (one A record
+and one AAAA record) for each hostname associated with the service object of type loadbalancer.
+
+[5]: https://kubernetes-sigs.github.io/aws-load-balancer-controller/v2.7/guide/service/annotations/#ip-address-type
+
+Example:
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  name: echoserver
+  annotations:
+    service.beta.kubernetes.io/aws-load-balancer-type: external
+    service.beta.kubernetes.io/aws-load-balancer-ip-address-type: dualstack
+spec:
+  selector:
+    app: echoserver
+  ports:
+    - port: 80
+      targetPort: 8080
+      protocol: TCP
+  type: LoadBalancer
+```
+
+The above Service object will result in the creation of a NLB with a dualstack
+interface. 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 NLB.

source/service.go

@@ -63,6 +63,13 @@ type serviceSource struct {
 	labelSelector                  labels.Selector
 }
 
+const (
+	// nlbDualstackAnnotationKey is the annotation used for determining if an NLB svc is dualstack
+	nlbDualstackAnnotationKey = "service.beta.kubernetes.io/aws-load-balancer-ip-address-type"
+	// nlbDualstackAnnotationValue is the value of the NLB dualstack annotation that indicates it is dualstack
+	nlbDualstackAnnotationValue = "dualstack"
+)
+
 // NewServiceSource creates a new serviceSource with the given config.
 func NewServiceSource(ctx context.Context, kubeClient kubernetes.Interface, namespace, annotationFilter string, fqdnTemplate string, combineFqdnAnnotation bool, compatibility string, publishInternal bool, publishHostIP bool, alwaysPublishNotReadyAddresses bool, serviceTypeFilter []string, ignoreHostnameAnnotation bool, labelSelector labels.Selector, resolveLoadBalancerHostname bool) (Source, error) {
 	tmpl, err := parseTemplate(fqdnTemplate)
@@ -197,6 +204,7 @@ func (sc *serviceSource) Endpoints(ctx context.Context) ([]*endpoint.Endpoint, e
 
 		log.Debugf("Endpoints generated from service: %s/%s: %v", svc.Namespace, svc.Name, svcEndpoints)
 		sc.setResourceLabel(svc, svcEndpoints)
+		sc.setDualstackLabel(svc, svcEndpoints)
 		endpoints = append(endpoints, svcEndpoints...)
 	}
 
@@ -236,7 +244,6 @@ func (sc *serviceSource) Endpoints(ctx context.Context) ([]*endpoint.Endpoint, e
 	for _, ep := range endpoints {
 		sort.Sort(ep.Targets)
 	}
-
 	return endpoints, nil
 }
 
@@ -459,6 +466,16 @@ func (sc *serviceSource) setResourceLabel(service *v1.Service, endpoints []*endp
 	}
 }
 
+func (sc *serviceSource) setDualstackLabel(service *v1.Service, endpoints []*endpoint.Endpoint) {
+	val, ok := service.Annotations[nlbDualstackAnnotationKey]
+	if ok && val == nlbDualstackAnnotationValue {
+		log.Debugf("Adding dualstack label to service %s/%s.", service.Namespace, service.Name)
+		for _, ep := range endpoints {
+			ep.Labels[endpoint.DualstackLabelKey] = "true"
+		}
+	}
+}
+
 func (sc *serviceSource) generateEndpoints(svc *v1.Service, hostname string, providerSpecific endpoint.ProviderSpecific, setIdentifier string, useClusterIP bool) (endpoints []*endpoint.Endpoint) {
 	hostname = strings.TrimSuffix(hostname, ".")
 

source/service_test.go

@@ -243,6 +243,31 @@ func testServiceSourceEndpoints(t *testing.T) {
 				{DNSName: "foo.example.org", RecordType: endpoint.RecordTypeA, Targets: endpoint.Targets{"1.2.3.4"}},
 			},
 		},
+		{
+			title:        "annotated dualstack services return an endpoint with dualstack label",
+			svcNamespace: "testing",
+			svcName:      "foo",
+			svcType:      v1.ServiceTypeLoadBalancer,
+			labels:       map[string]string{},
+			annotations: map[string]string{
+				hostnameAnnotationKey:     "foo.example.org.",
+				nlbDualstackAnnotationKey: nlbDualstackAnnotationValue,
+			},
+			externalIPs:        []string{},
+			lbs:                []string{"https://www.example.com"},
+			serviceTypesFilter: []string{},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName:    "foo.example.org",
+					RecordType: endpoint.RecordTypeCNAME,
+					Targets:    endpoint.Targets{"https://www.example.com"},
+					Labels: endpoint.Labels{
+						"resource":  "service/testing/foo",
+						"dualstack": "true",
+					},
+				},
+			},
+		},
 		{
 			title:                    "hostname annotation on services is ignored",
 			svcNamespace:             "testing",