Cannot load HTTPBackendRef default/external-service: type ExternalName is not supported for Kubernetes Service reference

Traefik Traefik v3 (latest)
1

I want to replace my kubernetes-ingress for my external services. I tried to use the gateway api. So I configured the GatewayClass, a Gateway and a HTTPRoute. Everything is working smooth for an internal service (for testing I choosed the whois service).

Then I changed the HTTPRoute to point to a service of type ExternalName. Then I get

>kubectl describe httproute external-https
Name:         external-https
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  gateway.networking.k8s.io/v1
Kind:         HTTPRoute
Metadata:
  Creation Timestamp:  2025-10-13T13:07:02Z
  Generation:          1
  Resource Version:    24517032
  UID:                 ef856042-95fc-4cab-89b5-54c74eca7371
Spec:
  Hostnames:
    external.example.com
  Parent Refs:
    Group:         gateway.networking.k8s.io
    Kind:          Gateway
    Name:          traefik
    Section Name:  https-external
  Rules:
    Backend Refs:
      Group:   
      Kind:    Service
      Name:    external-service
      Port:    80
      Weight:  1
    Matches:
      Path:
        Type:   PathPrefix
        Value:  /
Status:
  Parents:
    Conditions:
      Last Transition Time:  2025-10-13T13:07:02Z
      Message:               
      Observed Generation:   1
      Reason:                Accepted
      Status:                True
      Type:                  Accepted
      Last Transition Time:  2025-10-13T13:07:02Z
      Message:               Cannot load HTTPBackendRef default/external-service: type ExternalName is not supported for Kubernetes Service reference
      Observed Generation:   1
      Reason:                BackendNotFound
      Status:                False
      Type:                  ResolvedRefs
    Controller Name:         traefik.io/gateway-controller
    Parent Ref:
      Group:         gateway.networking.k8s.io
      Kind:          Gateway
      Name:          traefik
      Section Name:  https-external
Events:              <none>

>kubectl -n kube-system logs traefik-yyyyyyyyyy-xxxxx
...
2025-10-13T14:07:42Z INF Starting provider *gateway.Provider
2025-10-13T14:07:42Z INF ExternalName service loading is enabled, please ensure that this is expected (see AllowExternalNameServices option) providerName=kubernetes
2025-10-13T14:07:42Z INF ExternalName service loading is enabled, please ensure that this is expected (see AllowExternalNameServices option) providerName=kubernetescrd
2025-10-13T14:07:42Z INF Starting provider *acme.ChallengeTLSALPN
2025-10-13T14:07:42Z ERR Unable to load HTTPRoute backend: Cannot load HTTPBackendRef default/external-service: type ExternalName is not supported for Kubernetes Service reference http_route=external-https namespace=default providerName=kubernetesgateway
...

I can reference the service of type ExternalName by an Ingress.

Is it not supported by the gateway-api itself or is it just not supported by Traefik? or is there anything to configure?

If it is not supported, are there plans to support such scenario in the future?

2

Vegard S. Hagen has been able to reference a service with type ExternalName at External services with Gateway API with Cilium. So it seems that the Kubernetes gateway-api supports such constellation.

3

The Kubernetes gateway API Documentation states that for the Kind attribute in a BackendRef the following applies :

ExternalName services can refer to CNAME DNS records that may live
outside of the cluster and as such are difficult to reason about in
terms of conformance. They also may not be safe to forward to (see
CVE-2021-25740 for more information). Implementations SHOULD NOT
support ExternalName Services.
Support: Core (Services with a type other than ExternalName)
Support: Implementation-specific (Services with type ExternalName)

It may be that Traefik proxy only implemented the Core.