Envoy Gateway returns 503

Envoy Gateway returns 503 for Knative ExternalName backend (no endpoints) when using Gateway API

Summary

When using **Knative with **Gateway API (via net-gateway + **Envoy Gateway), Knative generates HTTPRoute resources that reference a Service of type ExternalName.

However, Envoy Gateway requires backends to have resolvable endpoints, and ExternalName Services do not create endpoints. This results in:

• 503 Service Unavailable.
• EndpointsNotFound condition on the HTTPRoute
• Envoy is unable to route traffic

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Expected Behavior

Knative-generated Gateway API resources should be fully compatible with Envoy Gateway and result in:

• Valid upstream clusters
• Successful routing to Knative services
• No dependency on endpoint-less Service types for HTTPRoute backends

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Actual Behavior

The generated HTTPRoute includes:

backendRefs:
  - name: website
    port: 80

Where the referenced Service is:

kind: Service
type: ExternalName
externalName: knative-internal.envoy-gateway-system.svc.cluster.local

Result:

• No Endpoints object exists

• Envoy Gateway reports:

  Failed to find endpoints: no ready endpoints for the related Service
  

• Requests return:

  503 Service Unavailable
  

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Observations

• The HTTPRoute is Accepted and ResolvedRefs=True
• But BackendsAvailable=False due to missing endpoints
• Direct requests to the internal gateway service work
• Routing through this ExternalName-based Service fails

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Reproduction Steps

1. Install Knative Serving with Gateway API (net-gateway + Envoy Gateway)
2. Create a Knative Service
3. Create a DomainMapping (or similar) that generates an HTTPRoute
4. Observe that the generated backend Service is of type ExternalName
5. Send request via external gateway

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Result

Envoy Gateway fails to route due to missing endpoints for ExternalName Service.

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Relevant Logs

Envoy access log:

{
  "response_code": 503,
  "response_code_details": "via_upstream",
  "upstream_cluster": null,
  "upstream_host": null
}

HTTPRoute status:

BackendsAvailable: False
Reason: EndpointsNotFound

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Question

Is the use of ExternalName Services for HTTPRoute backends expected with Gateway API?

If so:

• How should Envoy Gateway resolve these backends?
• Is additional configuration required?

If not:

• Should Knative net-gateway generate ClusterIP Services instead?

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Suggested Fix / Direction

Possible options:

1. Avoid using ExternalName Services for HTTPRoute backends
2. Generate a ClusterIP Service with real endpoints
3. Document required configuration for Envoy Gateway compatibility

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Environment

• Knative Serving: v1.20.2
• Gateway API: v1.4.1
• Envoy Gateway: v1.7.2
• Kubernetes: v1.32.9+rke2r1
• CNI: Cilium

Start by reproducing the Gateway API setup described in the issue and tracing the generated HTTPRoute and ExternalName Service in net-gateway-api. There is no source file or test named in the report. Done means establishing the expected backend behavior, choosing a compatible implementation or documentation change, and verifying that Envoy Gateway no longer reports EndpointsNotFound or returns 503.