QUIC listener always announce Gateway port in alt-svc and there is no way to configure it

[Owersun]

Description:
When enabling http3 on clientTrafficPolicy to make envoy accept QUIC packets, it announce "alt-svc" header with http3 port hint. And that port is taken directly from Gateway resource. The problem is that envoy-gateway is not always first link in the chain to receive client packets. In managed k8s clusters there could be provider loadbalancers/DDoS protecting front's before the actual envoy, and envoy could be exposed to listen on a different port than external loadbalancer accept client connections on.
Would be nice to have an option in http3 section of clienttrafficpolicy to manually configure which port is injected as alt-svc header.

[arkodg]

can be added to

gateway/api/v1alpha1/clienttrafficpolicy_types.go

Line 400 in 21dc566

type HTTP3Settings struct{}

[iamhaseebn]

Would this API shape work?

spec:
  http3:
    advertisedPort: 443

advertisedPort would be an optional gatewayv1.PortNumber on HTTP3Settings. When set, it would only override the port used in the generated alt-svc header; the listener and Service ports would stay unchanged. When omitted, behavior would remain unchanged and continue using the listener's external port. I'd cover both paths in the gateway-to-IR and xDS translator tests and update the HTTP/3 docs.

If that direction looks right, the API change can go first as the PR template recommends.

[Owersun]

Absolutely, this is exactly what I was asking/proposing for to have.