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fix(source/service): headless records and root/base domain (#5624 )

Signed-off-by: ivan katliarchuk <ivan.katliarchuk@gmail.com>

2025-07-09 00:43:28 -07:00

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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.

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 the domain 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 overrides any automatically derived hostnames (e.g., from Ingress.spec.rules[].host).
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/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.

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.

Unless the --ignore-hostname-annotation flag is specified. ↩︎
The annotation must be on the Gateway. ↩︎
The annotation must be on the listener's VirtualService. ↩︎
Only behaves differently than hostname for Services of type ClusterIP or LoadBalancer. ↩︎
Also supported on Pods referenced from a headless Service's Endpoints. ↩︎

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