Merge pull request #1696 from dansimone/dansimone/support-prefer-ingress-annotations

Optional ability to use the host name defined on an ingress's annotations *instead* of its hosts stanza

docs/faq.md

@@ -40,7 +40,9 @@ Services exposed via `type=LoadBalancer`, `type=ExternalName` and for the hostna
 
 There are three sources of information for ExternalDNS to decide on DNS name. ExternalDNS will pick one in order as listed below:
 
-1. For ingress objects ExternalDNS will create a DNS record based on the host specified for the ingress object. For services ExternalDNS will look for the annotation `external-dns.alpha.kubernetes.io/hostname` on the service and use the loadbalancer IP, it also will look for the annotation `external-dns.alpha.kubernetes.io/internal-hostname` on the service and use the service IP.
+1. For ingress objects ExternalDNS will create a DNS record based on the hosts specified for the ingress object, as well as the `external-dns.alpha.kubernetes.io/hostname` annotation. For services ExternalDNS will look for the annotation `external-dns.alpha.kubernetes.io/hostname` on the service and use the loadbalancer IP, it also will look for the annotation `external-dns.alpha.kubernetes.io/internal-hostname` on the service and use the service IP.
+    - For ingresses, you can optionally force ExternalDNS to create records based on _either_ the hosts specified or the `external-dns.alpha.kubernetes.io/hostname` annotation. This behavior is controlled by
+      setting the `external-dns.alpha.kubernetes.io/ingress-hostname-source` annotation on that ingress to either `defined-hosts-only` or `annotation-only`.
 
 2. If compatibility mode is enabled (e.g. `--compatibility={mate,molecule}` flag), External DNS will parse annotations used by Zalando/Mate, wearemolecule/route53-kubernetes. Compatibility mode with Kops DNS Controller is planned to be added in the future.
 

source/ingress.go

@@ -42,6 +42,10 @@ const (
 	ALBDualstackAnnotationKey = "alb.ingress.kubernetes.io/ip-address-type"
 	// ALBDualstackAnnotationValue is the value of the ALB dualstack annotation that indicates it is dualstack
 	ALBDualstackAnnotationValue = "dualstack"
+
+	// Possible values for the ingress-hostname-source annotation
+	IngressHostnameSourceAnnotationOnlyValue   = "annotation-only"
+	IngressHostnameSourceDefinedHostsOnlyValue = "defined-hosts-only"
 )
 
 // ingressSource is an implementation of Source for Kubernetes ingress objects.
@@ -243,8 +247,6 @@ func (sc *ingressSource) setDualstackLabel(ingress *v1beta1.Ingress, endpoints [
 
 // endpointsFromIngress extracts the endpoints from ingress object
 func endpointsFromIngress(ing *v1beta1.Ingress, ignoreHostnameAnnotation bool, ignoreIngressTLSSpec bool) []*endpoint.Endpoint {
-	var endpoints []*endpoint.Endpoint
-
 	ttl, err := getTTLFromAnnotations(ing.Annotations)
 	if err != nil {
 		log.Warn(err)
@@ -258,11 +260,13 @@ func endpointsFromIngress(ing *v1beta1.Ingress, ignoreHostnameAnnotation bool, i
 
 	providerSpecific, setIdentifier := getProviderSpecificAnnotations(ing.Annotations)
 
+	// Gather endpoints defined on hosts sections of the ingress
+	var definedHostsEndpoints []*endpoint.Endpoint
 	for _, rule := range ing.Spec.Rules {
 		if rule.Host == "" {
 			continue
 		}
-		endpoints = append(endpoints, endpointsForHostname(rule.Host, targets, ttl, providerSpecific, setIdentifier)...)
+		definedHostsEndpoints = append(definedHostsEndpoints, endpointsForHostname(rule.Host, targets, ttl, providerSpecific, setIdentifier)...)
 	}
 
 	// Skip endpoints if we do not want entries from tls spec section
@@ -272,18 +276,33 @@ func endpointsFromIngress(ing *v1beta1.Ingress, ignoreHostnameAnnotation bool, i
 				if host == "" {
 					continue
 				}
-				endpoints = append(endpoints, endpointsForHostname(host, targets, ttl, providerSpecific, setIdentifier)...)
+				definedHostsEndpoints = append(definedHostsEndpoints, endpointsForHostname(host, targets, ttl, providerSpecific, setIdentifier)...)
 			}
 		}
 	}
 
-	// Skip endpoints if we do not want entries from annotations
+	// Gather endpoints defined on annotations in the ingress
+	var annotationEndpoints []*endpoint.Endpoint
 	if !ignoreHostnameAnnotation {
-		hostnameList := getHostnamesFromAnnotations(ing.Annotations)
+		for _, hostname := range getHostnamesFromAnnotations(ing.Annotations) {
-		for _, hostname := range hostnameList {
+			annotationEndpoints = append(annotationEndpoints, endpointsForHostname(hostname, targets, ttl, providerSpecific, setIdentifier)...)
-			endpoints = append(endpoints, endpointsForHostname(hostname, targets, ttl, providerSpecific, setIdentifier)...)
 		}
 	}
+
+	// Determine which hostnames to consider in our final list
+	hostnameSourceAnnotation, hostnameSourceAnnotationExists := ing.Annotations[ingressHostnameSourceKey]
+	if !hostnameSourceAnnotationExists {
+		return append(definedHostsEndpoints, annotationEndpoints...)
+	}
+
+	// Include endpoints according to the hostname source annotation in our final list
+	var endpoints []*endpoint.Endpoint
+	if strings.ToLower(hostnameSourceAnnotation) == IngressHostnameSourceDefinedHostsOnlyValue {
+		endpoints = append(endpoints, definedHostsEndpoints...)
+	}
+	if strings.ToLower(hostnameSourceAnnotation) == IngressHostnameSourceAnnotationOnlyValue {
+		endpoints = append(endpoints, annotationEndpoints...)
+	}
 	return endpoints
 }
 

source/ingress_test.go

@@ -85,6 +85,7 @@ func (suite *IngressSuite) TestDualstackLabelIsSet() {
 func TestIngress(t *testing.T) {
 	suite.Run(t, new(IngressSuite))
 	t.Run("endpointsFromIngress", testEndpointsFromIngress)
+	t.Run("endpointsFromIngressHostnameSourceAnnotation", testEndpointsFromIngressHostnameSourceAnnotation)
 	t.Run("Endpoints", testIngressEndpoints)
 }
 
@@ -228,6 +229,98 @@ func testEndpointsFromIngress(t *testing.T) {
 	}
 }
 
+func testEndpointsFromIngressHostnameSourceAnnotation(t *testing.T) {
+	// Host names and host name annotation provided, with various values of the ingress-hostname-source annotation
+	for _, ti := range []struct {
+		title    string
+		ingress  fakeIngress
+		expected []*endpoint.Endpoint
+	}{
+		{
+			title: "No ingress-hostname-source annotation, one rule.host, one annotation host",
+			ingress: fakeIngress{
+				dnsnames:    []string{"foo.bar"},
+				annotations: map[string]string{hostnameAnnotationKey: "foo.baz"},
+				hostnames:   []string{"lb.com"},
+			},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName: "foo.bar",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+				{
+					DNSName: "foo.baz",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+			},
+		},
+		{
+			title: "No ingress-hostname-source annotation, one rule.host",
+			ingress: fakeIngress{
+				dnsnames:    []string{"foo.bar"},
+				hostnames:   []string{"lb.com"},
+			},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName: "foo.bar",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+			},
+		},
+		{
+			title: "No ingress-hostname-source annotation, one rule.host, one annotation host",
+			ingress: fakeIngress{
+				dnsnames:    []string{"foo.bar"},
+				annotations: map[string]string{hostnameAnnotationKey: "foo.baz"},
+				hostnames:   []string{"lb.com"},
+			},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName: "foo.bar",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+				{
+					DNSName: "foo.baz",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+			},
+		},
+		{
+			title: "Ingress-hostname-source=defined-hosts-only, one rule.host, one annotation host",
+			ingress: fakeIngress{
+				dnsnames:    []string{"foo.bar"},
+				annotations: map[string]string{hostnameAnnotationKey: "foo.baz", ingressHostnameSourceKey: "defined-hosts-only"},
+				hostnames:   []string{"lb.com"},
+			},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName: "foo.bar",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+			},
+		},
+		{
+			title: "Ingress-hostname-source=annotation-only, one rule.host, one annotation host",
+			ingress: fakeIngress{
+				dnsnames:    []string{"foo.bar"},
+				annotations: map[string]string{hostnameAnnotationKey: "foo.baz", ingressHostnameSourceKey: "annotation-only"},
+				hostnames:   []string{"lb.com"},
+			},
+			expected: []*endpoint.Endpoint{
+				{
+					DNSName: "foo.baz",
+					Targets: endpoint.Targets{"lb.com"},
+				},
+			},
+		},
+	} {
+		t.Run(ti.title, func(t *testing.T) {
+			realIngress := ti.ingress.Ingress()
+			validateEndpoints(t, endpointsFromIngress(realIngress, false, false), ti.expected)
+		})
+	}
+}
+
 func testIngressEndpoints(t *testing.T) {
 	namespace := "testing"
 	for _, ti := range []struct {

source/source.go

@@ -46,6 +46,9 @@ const (
 	ttlAnnotationKey = "external-dns.alpha.kubernetes.io/ttl"
 	// The annotation used for switching to the alias record types e. g. AWS Alias records instead of a normal CNAME
 	aliasAnnotationKey = "external-dns.alpha.kubernetes.io/alias"
+	// The annotation used to determine the source of hostnames for ingresses.  This is an optional field - all
+	// available hostname sources are used if not specified.
+	ingressHostnameSourceKey = "external-dns.alpha.kubernetes.io/ingress-hostname-source"
 	// The value of the controller annotation so that we feel responsible
 	controllerAnnotationValue = "dns-controller"
 	// The annotation used for defining the desired hostname