external-dns/docs/annotations/annotations.md

Annotations

ExternalDNS sources support a number of annotations on the Kubernetes resources that they examine.

The following table documents which sources support which annotations:

Source	controller	hostname	internal-hostname	target	ttl	(provider-specific)
Ambassador				Yes	Yes	Yes
Connector
Contour	Yes	Yes1		Yes	Yes	Yes
CloudFoundry
CRD
F5				Yes	Yes
Gateway	Yes	Yes1		Yes2	Yes	Yes
Gloo				Yes	Yes3	Yes3
Ingress	Yes	Yes1		Yes	Yes	Yes
Istio	Yes	Yes1		Yes	Yes	Yes
Kong		Yes1		Yes	Yes	Yes
Node	Yes			Yes	Yes
OpenShift	Yes	Yes1		Yes	Yes	Yes
Pod		Yes	Yes	Yes
Service	Yes	Yes1	Yes14	Yes5	Yes	Yes
Skipper	Yes	Yes1		Yes	Yes	Yes
Traefik		Yes1		Yes	Yes	Yes

external-dns.alpha.kubernetes.io/access

Specifies which set of node IP addresses to use for a Service of type NodePort.

If the value is public, use the Nodes' addresses of type ExternalIP, plus IPv6 addresses of type InternalIP.

If the value is private, use the Nodes' addresses of type InternalIP.

If the annotation is not present and there is at least one address of type ExternalIP, behave as if the value were public, otherwise behave as if the value were private.

external-dns.alpha.kubernetes.io/controller

If this annotation exists and has a value other than dns-controller then the source ignores the resource.

external-dns.alpha.kubernetes.io/endpoints-type

Specifies which set of addresses to use for a headless Service.

Supported values:

• NodeExternalIP. Required --service-type-filter=ClusterIP and --service-type-filter=Node or no --service-type-filter flag specified.
• HostIP.

If the value is NodeExternalIP, use each relevant Pod's Node's address of type ExternalIP plus each IPv6 address of type InternalIP.

Otherwise, if the value is HostIP or the --publish-host-ip flag is specified, use each relevant Pod's Status.HostIP.

Otherwise, use the IP of each of the Service's Endpoints's Addresses.

external-dns.alpha.kubernetes.io/hostname

Specifies additional domains for the resource's DNS records.

Multiple hostnames can be specified through a comma-separated list, e.g. svc.mydomain1.com,svc.mydomain2.com.

For Pods, uses the Pod's Status.PodIP, unless they are hostNetwork: true in which case the NodeExternalIP is used for IPv4 and NodeInternalIP for IPv6.

Notes:

• This annotation can override or add extra hostnames alongside any automatically derived hostnames (e.g., from Ingress.spec.rules[].host).
• The ingress-hostname-source annotation may be used to specify where to get the domain for an Ingress resource.
• Hostnames must match the domain filter set in ExternalDNS (e.g., --domain-filter=example.com).
• This is an alpha annotation — subject to change; newer versions may support alternatives or deprecate it.
• This annotation is helpful for:
  • Services or other resources without native hostname fields.
  • Explicit overrides or multi-host situations.
  • Avoiding reliance on auto-detection or heuristics.

Use Cases for external-dns.alpha.kubernetes.io/hostname annotation

Explicit Hostname Mapping for Services

You have a Service (e.g. of type LoadBalancer or ClusterIP) and want to expose it under a custom DNS name:

apiVersion: v1
kind: Service
metadata:
  name: my-service
  annotations:
    external-dns.alpha.kubernetes.io/hostname: app.example.com
spec:
  type: LoadBalancer
  ...

ExternalDNS will create a A or CNAME record for app.example.com pointing to the external IP or hostname of the service.

Multi-Hostname Records

You can assign multiple hostnames by separating them with commas:

annotations:
  external-dns.alpha.kubernetes.io/hostname: api.example.com,api.internal.example.com

ExternalDNS will create two DNS records for the same service.

Static DNS Assignment Without Ingress Rules

When using Ingress, you usually declare hostnames in the spec.rules[].host. But with this annotation, you can manage DNS independently:

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: my-ingress
  annotations:
    external-dns.alpha.kubernetes.io/hostname: www.example.com
spec:
  rules:
    - http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: my-service
                port:
                  number: 80

Useful when DNS management is decoupled from routing logic.

external-dns.alpha.kubernetes.io/ingress-hostname-source

Specifies where to get the domain for an Ingress resource.

If the value is defined-hosts-only, use only the domains from the Ingress spec.

If the value is annotation-only, use only the domains from the Ingress annotations.

If the annotation is not present, use the domains from both the spec and annotations.

external-dns.alpha.kubernetes.io/ingress

This annotation allows ExternalDNS to work with Istio & GlooEdge Gateways that don't have a public IP.

It can be used to address a specific architectural pattern, when a Kubernetes Ingress directs all public traffic to an Istio or GlooEdge Gateway:

• The Challenge: By default, ExternalDNS sources the public IP address for a DNS record from a Service of type LoadBalancer. However, in some setups, the Gateway's Service is of type ClusterIP, with all public traffic routed to it via a separate Kubernetes Ingress object. This setup leaves the Gateway without a public IP that ExternalDNS can discover.

• The Solution: The annotation on the Istio/GlooEdge Gateway tells ExternalDNS to ignore the Gateway's Service IP. Instead, it directs ExternalDNS to a specified Ingress resource to find the target LoadBalancer IP address.

Use Cases for external-dns.alpha.kubernetes.io/ingress annotation

Getting target from Ingress backed Gloo Gateway

apiVersion: gateway.solo.io/v1
kind: Gateway
metadata:
  annotations:
    external-dns.alpha.kubernetes.io/ingress: gateway-proxy
  labels:
    app: gloo
  name: gateway-proxy
  namespace: gloo-system
spec:
  bindAddress: '::'
  bindPort: 8080
  options: {}
  proxyNames:
  - gateway-proxy
  ssl: false
  useProxyProto: false
---
apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: gateway-proxy
  namespace: gloo-system
spec:
  ingressClassName: alb
  rules:
  - host: cool-service.example.com
    http:
      paths:
      - backend:
          service:
            name: gateway-proxy
            port:
              name: http
        path: /
        pathType: Prefix
status:
  loadBalancer:
    ingress:
    - hostname: k8s-alb-c4aa37c880-740590208.us-east-1.elb.amazonaws.com
---
# This object is generated by GlooEdge Control Plane from Gateway and VirtualService.
# We have no direct control on this resource
apiVersion: gloo.solo.io/v1
kind: Proxy
metadata:
  labels:
    created_by: gloo-gateway
  name: gateway-proxy
  namespace: gloo-system
spec:
  listeners:
  - bindAddress: '::'
    bindPort: 8080
    httpListener:
      virtualHosts:
      - domains:
        - cool-service.example.com
        metadataStatic:
          sources:
          - observedGeneration: "6652"
            resourceKind: '*v1.VirtualService'
            resourceRef:
              name: cool-service
              namespace: gloo-system
        name: cool-service
        routes:
        - matchers:
          - prefix: /
          metadataStatic:
            sources:
            - observedGeneration: "6652"
              resourceKind: '*v1.VirtualService'
              resourceRef:
                name: cool-service
                namespace: gloo-system
            upgrades:
            - websocket: {}
    metadataStatic:
      sources:
      - observedGeneration: "6111"
        resourceKind: '*v1.Gateway'
        resourceRef:
          name: gateway-proxy
          namespace: gloo-system
    name: listener-::-8080
    useProxyProto: false

external-dns.alpha.kubernetes.io/internal-hostname

Specifies the domain for the resource's DNS records that are for use from internal networks.

For Services of type LoadBalancer, uses the Service's ClusterIP.

For Pods, uses the Pod's Status.PodIP, unless they are hostNetwork: true in which case the NodeExternalIP is used for IPv4 and NodeInternalIP for IPv6.

external-dns.alpha.kubernetes.io/target

Specifies a comma-separated list of values to override the resource's DNS record targets (RDATA).

Targets that parse as IPv4 addresses are published as A records and targets that parse as IPv6 addresses are published as AAAA records. All other targets are published as CNAME records.

external-dns.alpha.kubernetes.io/ttl

Specifies the TTL (time to live) for the resource's DNS records.

The value may be specified as either a duration or an integer number of seconds. It must be between 1 and 2,147,483,647 seconds.

Note; setting the value to 0 means, that TTL is not configured and thus use default.

Provider-specific annotations

Some providers define their own annotations. Cloud-specific annotations have keys prefixed as follows:

Cloud	Annotation prefix
AWS	external-dns.alpha.kubernetes.io/aws-
CloudFlare	external-dns.alpha.kubernetes.io/cloudflare-
Scaleway	external-dns.alpha.kubernetes.io/scw-

Additional annotations that are currently implemented only by AWS are:

external-dns.alpha.kubernetes.io/alias

If the value of this annotation is true, specifies that CNAME records generated by the resource should instead be alias records.

This annotation is only relevant if the --aws-prefer-cname flag is specified.

external-dns.alpha.kubernetes.io/set-identifier

Specifies the set identifier for DNS records generated by the resource.

A set identifier differentiates among multiple DNS record sets that have the same combination of domain and type. Which record set or sets are returned to queries is then determined by the configured routing policy.

Gateway API Annotation Placement

When using Gateway API sources (gateway-httproute, gateway-grpcroute, gateway-tlsroute, etc.), annotations are read from different resources: Gateway resource reads only target annotation, while Route resources (HTTPRoute, GRPCRoute, TLSRoute, etc.) read all other annotations (hostname, ttl, controller, and provider-specific annotations like cloudflare-*, aws-*, scw-*).

For more details and comprehensive examples, see the Gateway API documentation.

---

1. Unless the --ignore-hostname-annotation flag is specified. ↩︎

2. For Gateway API sources, annotation placement differs by type. See Gateway API Annotation Placement for details. ↩︎

3. The annotation must be on the listener's VirtualService. ↩︎

4. Only behaves differently than hostname for Services of type ClusterIP or LoadBalancer. ↩︎

5. Also supported on Pods referenced from a headless Service's Endpoints. ↩︎