feat(aws): support alias=A and alias=AAAA to create single record type

docs/annotations/annotations.md

@@ -358,6 +358,37 @@ Additional annotations implemented by specific providers:
 If the value of this annotation is `true`, specifies that CNAME records generated by the
 resource should instead be alias records.
 
+Additionally, you can set the value to `A` or `AAAA` to create only one type of alias record:
+
+- `A`: Creates only an A alias record (IPv4 only)
+- `AAAA`: Creates only an AAAA alias record (IPv6 only)
+
+This is useful when your alias target is IPv4-only (i.e., it does not have an AAAA target),
+and creating an AAAA alias record would fail.
+
+Note: The `A` and `AAAA` values are currently only supported by the AWS Route53 provider.
+
+#### Example: IPv4-only alias target
+
+```yaml
+apiVersion: v1
+kind: Service
+metadata:
+  name: my-app
+  namespace: default
+  annotations:
+    external-dns.alpha.kubernetes.io/hostname: app.example.com
+    external-dns.alpha.kubernetes.io/target: ipv4-only-target.example.com
+    # Create only an A (IPv4) alias record to avoid creating an AAAA alias record for an IPv4-only target.
+    external-dns.alpha.kubernetes.io/alias: "A"
+spec:
+  type: LoadBalancer
+  ports:
+    - port: 80
+  selector:
+    app: my-app
+```
+
 This annotation is only supported on A, AAAA, and CNAME record types. Endpoints with other
 record types (e.g. MX, SRV, TXT) that have this annotation set will be rejected.
 

docs/tutorials/aws.md

@@ -710,6 +710,13 @@ To make the target an alias, the ingress needs to be configured correctly as des
 In particular, the argument `--publish-service=default/nginx-ingress-controller` has to be set on the `nginx-ingress-controller` container.
 If one uses the `nginx-ingress` Helm chart, this flag can be set with the `controller.publishService.enabled` configuration option.
 
+Additionally, you can set the value to `A` or `AAAA` to create only one type of ALIAS record:
+
+- `A`: Creates only an A ALIAS record (IPv4 only)
+- `AAAA`: Creates only an AAAA ALIAS record (IPv6 only)
+
+Note: The `A` and `AAAA` values are currently only supported by the AWS Route53 provider.
+
 ### target-hosted-zone
 
 `external-dns.kubernetes.io/aws-target-hosted-zone` can optionally be set to the ID of a Route53 hosted zone. This will force external-dns to use the specified hosted zone when creating an ALIAS target.

endpoint/endpoint.go

@@ -336,6 +336,36 @@ func (e *Endpoint) GetProviderSpecificProperty(key string) (string, bool) {
 	return "", false
 }
 
+type AliasType string
+
+const (
+	// AliasNone indicates alias property is not set
+	AliasNone AliasType = ""
+	// AliasFalse indicates alias property is set to false
+	AliasFalse AliasType = "false"
+	// AliasTrue indicates alias property is set to true (both A and AAAA)
+	AliasTrue AliasType = "true"
+	// AliasA indicates alias property is set to A record only
+	AliasA AliasType = "A"
+	// AliasAAAA indicates alias property is set to AAAA record only
+	AliasAAAA AliasType = "AAAA"
+)
+
+func (e *Endpoint) GetAliasProperty() AliasType {
+	switch a, ok := e.GetProviderSpecificProperty("alias"); {
+	case a == "true" && ok:
+		return AliasTrue
+	case a == "false" && ok:
+		return AliasFalse
+	case a == "A" && ok:
+		return AliasA
+	case a == "AAAA" && ok:
+		return AliasAAAA
+	default:
+		return AliasNone
+	}
+}
+
 // GetBoolProviderSpecificProperty returns a boolean provider-specific property value.
 func (e *Endpoint) GetBoolProviderSpecificProperty(key string) (bool, bool) {
 	prop, ok := e.GetProviderSpecificProperty(key)

endpoint/endpoint_test.go

@@ -1701,6 +1701,72 @@ func TestNewEndpointWithTTLPreservesDotsInTXTRecords(t *testing.T) {
 	assert.Equal(t, "target.example.com", cnameEndpoint.Targets[0], "CNAME record should have trailing dot trimmed")
 }
 
+func TestGetAliasProperty(t *testing.T) {
+	tests := []struct {
+		name     string
+		endpoint Endpoint
+		expected AliasType
+	}{
+		{
+			name:     "no alias property returns AliasNone",
+			endpoint: Endpoint{},
+			expected: AliasNone,
+		},
+		{
+			name: "alias=true returns AliasTrue",
+			endpoint: Endpoint{
+				ProviderSpecific: []ProviderSpecificProperty{
+					{Name: "alias", Value: "true"},
+				},
+			},
+			expected: AliasTrue,
+		},
+		{
+			name: "alias=false returns AliasFalse",
+			endpoint: Endpoint{
+				ProviderSpecific: []ProviderSpecificProperty{
+					{Name: "alias", Value: "false"},
+				},
+			},
+			expected: AliasFalse,
+		},
+		{
+			name: "alias=A returns AliasA",
+			endpoint: Endpoint{
+				ProviderSpecific: []ProviderSpecificProperty{
+					{Name: "alias", Value: "A"},
+				},
+			},
+			expected: AliasA,
+		},
+		{
+			name: "alias=AAAA returns AliasAAAA",
+			endpoint: Endpoint{
+				ProviderSpecific: []ProviderSpecificProperty{
+					{Name: "alias", Value: "AAAA"},
+				},
+			},
+			expected: AliasAAAA,
+		},
+		{
+			name: "alias with invalid value returns AliasNone",
+			endpoint: Endpoint{
+				ProviderSpecific: []ProviderSpecificProperty{
+					{Name: "alias", Value: "invalid"},
+				},
+			},
+			expected: AliasNone,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := tt.endpoint.GetAliasProperty()
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}
+
 func TestGetBoolProviderSpecificProperty(t *testing.T) {
 	tests := []struct {
 		name           string

provider/aws/aws.go

@@ -853,21 +853,13 @@ func (p *AWSProvider) AdjustEndpoints(endpoints []*endpoint.Endpoint) ([]*endpoi
 }
 
 func (p *AWSProvider) adjustEndpointAndNewAaaaIfNeeded(ep *endpoint.Endpoint) *endpoint.Endpoint {
-	var aaaa *endpoint.Endpoint
 	switch ep.RecordType {
 	case endpoint.RecordTypeA, endpoint.RecordTypeAAAA:
 		p.adjustAandAAAARecord(ep)
 	case endpoint.RecordTypeCNAME:
-		p.adjustCNAMERecord(ep)
-		adjustGeoProximityLocationEndpoint(ep)
-		if isAlias, _ := ep.GetBoolProviderSpecificProperty(endpoint.ProviderSpecificAlias); isAlias {
-			aaaa = ep.DeepCopy()
-			aaaa.RecordType = endpoint.RecordTypeAAAA
-		}
-		return aaaa
+		return p.adjustCNAMERecordAndNewAaaaIfNeeded(ep)
 	}
-	adjustGeoProximityLocationEndpoint(ep)
-	return aaaa
+	return nil
 }
 
 func (p *AWSProvider) adjustAliasRecord(ep *endpoint.Endpoint) {
@@ -886,39 +878,43 @@ func (p *AWSProvider) adjustAliasRecord(ep *endpoint.Endpoint) {
 }
 
 func (p *AWSProvider) adjustAandAAAARecord(ep *endpoint.Endpoint) {
-	isAlias, _ := ep.GetBoolProviderSpecificProperty(endpoint.ProviderSpecificAlias)
-	if isAlias {
+	if ep.GetAliasProperty() == endpoint.AliasTrue {
 		p.adjustAliasRecord(ep)
 	} else {
 		ep.DeleteProviderSpecificProperty(endpoint.ProviderSpecificAlias)
 		ep.DeleteProviderSpecificProperty(providerSpecificEvaluateTargetHealth)
 	}
+	adjustGeoProximityLocationEndpoint(ep)
 }
 
-func (p *AWSProvider) adjustCNAMERecord(ep *endpoint.Endpoint) {
-	isAlias, exists := ep.GetBoolProviderSpecificProperty(endpoint.ProviderSpecificAlias)
-
-	// fallback to determining alias based on preferCNAME if not explicitly set
-	if !exists {
-		isAlias = useAlias(ep, p.preferCNAME)
+func (p *AWSProvider) adjustCNAMERecordAndNewAaaaIfNeeded(ep *endpoint.Endpoint) *endpoint.Endpoint {
+	// ensure alias property is set
+	if ep.GetAliasProperty() == endpoint.AliasNone {
+		isAlias := useAlias(ep, p.preferCNAME)
 		log.Debugf("Modifying endpoint: %v, setting %s=%v", ep, endpoint.ProviderSpecificAlias, isAlias)
 		ep.SetProviderSpecificProperty(endpoint.ProviderSpecificAlias, strconv.FormatBool(isAlias))
 	}
 
-	// if not an alias, ensure alias properties are adjusted accordingly
-	if !isAlias {
-		if exists {
-			// normalize to string "false" when provider specific alias is set to false or other non-true value
-			ep.SetProviderSpecificProperty(endpoint.ProviderSpecificAlias, "false")
-		}
-		ep.DeleteProviderSpecificProperty(providerSpecificEvaluateTargetHealth)
-	}
-
-	// if an alias, convert to A record and adjust alias properties
-	if isAlias {
+	switch ep.GetAliasProperty() {
+	case endpoint.AliasTrue:
+		ep.RecordType = endpoint.RecordTypeA
+		p.adjustAliasRecord(ep)
+		adjustGeoProximityLocationEndpoint(ep)
+		aaaa := ep.DeepCopy()
+		aaaa.RecordType = endpoint.RecordTypeAAAA
+		return aaaa
+	case endpoint.AliasA:
 		ep.RecordType = endpoint.RecordTypeA
 		p.adjustAliasRecord(ep)
+	case endpoint.AliasAAAA:
+		ep.RecordType = endpoint.RecordTypeAAAA
+		p.adjustAliasRecord(ep)
+	case endpoint.AliasFalse:
+		ep.DeleteProviderSpecificProperty(providerSpecificEvaluateTargetHealth)
 	}
+
+	adjustGeoProximityLocationEndpoint(ep)
+	return nil
 }
 
 // if the endpoint is using geoproximity, set the bias to 0 if not set

provider/aws/aws_test.go

@@ -3308,6 +3308,66 @@ func TestAWSProvider_adjustEndpointAndNewAaaaIfNeeded(t *testing.T) {
 			},
 			expectedAaaa: nil,
 		},
+		{
+			name: "CNAME record with alias=A should convert to A record only and not create AAAA",
+			ep: &endpoint.Endpoint{
+				DNSName:    "test.foo.bar.",
+				RecordType: endpoint.RecordTypeCNAME,
+				Targets:    endpoint.Targets{"same-zone-target.foo.bar."},
+				ProviderSpecific: endpoint.ProviderSpecific{
+					{
+						Name:  endpoint.ProviderSpecificAlias,
+						Value: "A",
+					},
+				},
+			},
+			expected: &endpoint.Endpoint{
+				DNSName:    "test.foo.bar.",
+				RecordType: endpoint.RecordTypeA,
+				Targets:    endpoint.Targets{"same-zone-target.foo.bar."},
+				ProviderSpecific: endpoint.ProviderSpecific{
+					{
+						Name:  endpoint.ProviderSpecificAlias,
+						Value: "A",
+					},
+					{
+						Name:  providerSpecificEvaluateTargetHealth,
+						Value: "false",
+					},
+				},
+			},
+			expectedAaaa: nil,
+		},
+		{
+			name: "CNAME record with alias=AAAA should convert to AAAA record only and not create A",
+			ep: &endpoint.Endpoint{
+				DNSName:    "test.foo.bar.",
+				RecordType: endpoint.RecordTypeCNAME,
+				Targets:    endpoint.Targets{"same-zone-target.foo.bar."},
+				ProviderSpecific: endpoint.ProviderSpecific{
+					{
+						Name:  endpoint.ProviderSpecificAlias,
+						Value: "AAAA",
+					},
+				},
+			},
+			expected: &endpoint.Endpoint{
+				DNSName:    "test.foo.bar.",
+				RecordType: endpoint.RecordTypeAAAA,
+				Targets:    endpoint.Targets{"same-zone-target.foo.bar."},
+				ProviderSpecific: endpoint.ProviderSpecific{
+					{
+						Name:  endpoint.ProviderSpecificAlias,
+						Value: "AAAA",
+					},
+					{
+						Name:  providerSpecificEvaluateTargetHealth,
+						Value: "false",
+					},
+				},
+			},
+			expectedAaaa: nil,
+		},
 
 		// --- MX / other records ---
 		{

registry/txt/registry.go

@@ -252,8 +252,7 @@ func (im *TXTRegistry) Records(ctx context.Context) ([]*endpoint.Endpoint, error
 			SetIdentifier: ep.SetIdentifier,
 		}
 
-		// AWS Alias records have "new" format encoded as type "cname"
-		if isAlias, found := ep.GetBoolProviderSpecificProperty(endpoint.ProviderSpecificAlias); found && isAlias && ep.RecordType == endpoint.RecordTypeA {
+		if shouldUseCNAMEForTxtRecord(ep) {
 			key.RecordType = endpoint.RecordTypeCNAME
 		}
 
@@ -296,6 +295,13 @@ func (im *TXTRegistry) Records(ctx context.Context) ([]*endpoint.Endpoint, error
 	return endpoints, nil
 }
 
+// shouldUseCNAMEForTxtRecord checks if the endpoint is an alias A record converted from CNAME.
+// TXT ownership records use CNAME as the record type for such records.
+func shouldUseCNAMEForTxtRecord(ep *endpoint.Endpoint) bool {
+	aliasType := ep.GetAliasProperty()
+	return (aliasType == endpoint.AliasTrue || aliasType == endpoint.AliasA) && ep.RecordType == endpoint.RecordTypeA
+}
+
 // generateTXTRecord generates TXT records in either both formats (old and new) or new format only,
 // depending on the newFormatOnly configuration. The old format is maintained for backwards
 // compatibility but can be disabled to reduce the number of DNS records.
@@ -308,8 +314,8 @@ func (im *TXTRegistry) generateTXTRecordWithFilter(r *endpoint.Endpoint, filter
 
 	// Always create new format record
 	recordType := r.RecordType
-	// AWS Alias records are encoded as type "cname"
-	if isAlias, found := r.GetBoolProviderSpecificProperty(endpoint.ProviderSpecificAlias); found && isAlias && recordType == endpoint.RecordTypeA {
+
+	if shouldUseCNAMEForTxtRecord(r) {
 		recordType = endpoint.RecordTypeCNAME
 	}
 

registry/txt/registry_test.go

@@ -1091,6 +1091,7 @@ func testTXTRegistryApplyChangesNoPrefix(t *testing.T) {
 			newEndpointWithOwner("new-record-1.test-zone.example.org", "new-loadbalancer-1.lb.com", endpoint.RecordTypeCNAME, ""),
 			newEndpointWithOwner("example", "new-loadbalancer-1.lb.com", endpoint.RecordTypeCNAME, ""),
 			newEndpointWithOwner("new-alias.test-zone.example.org", "my-domain.com", endpoint.RecordTypeA, "").WithProviderSpecific(endpoint.ProviderSpecificAlias, "true"),
+			newEndpointWithOwner("new-alias-a-only.test-zone.example.org", "my-domain.com", endpoint.RecordTypeA, "").WithProviderSpecific(endpoint.ProviderSpecificAlias, "A"),
 		},
 		Delete: []*endpoint.Endpoint{
 			newEndpointWithOwner("foobar.test-zone.example.org", "foobar.loadbalancer.com", endpoint.RecordTypeCNAME, "owner"),
@@ -1110,6 +1111,8 @@ func testTXTRegistryApplyChangesNoPrefix(t *testing.T) {
 			newTXTEndpointWithOwnedRecord("cname-example", "\"heritage=external-dns,external-dns/owner=owner\"", "example"),
 			newEndpointWithOwner("new-alias.test-zone.example.org", "my-domain.com", endpoint.RecordTypeA, "owner").WithProviderSpecific(endpoint.ProviderSpecificAlias, "true"),
 			newTXTEndpointWithOwnedRecord("cname-new-alias.test-zone.example.org", "\"heritage=external-dns,external-dns/owner=owner\"", "new-alias.test-zone.example.org").WithProviderSpecific(endpoint.ProviderSpecificAlias, "true"),
+			newEndpointWithOwner("new-alias-a-only.test-zone.example.org", "my-domain.com", endpoint.RecordTypeA, "owner").WithProviderSpecific(endpoint.ProviderSpecificAlias, "A"),
+			newTXTEndpointWithOwnedRecord("cname-new-alias-a-only.test-zone.example.org", "\"heritage=external-dns,external-dns/owner=owner\"", "new-alias-a-only.test-zone.example.org").WithProviderSpecific(endpoint.ProviderSpecificAlias, "A"),
 		},
 		Delete: []*endpoint.Endpoint{
 			newEndpointWithOwner("foobar.test-zone.example.org", "foobar.loadbalancer.com", endpoint.RecordTypeCNAME, "owner"),