Clarify Conformance Expectations for Gateway Ports and Listeners

[robscott]

What would you like to be added:
As described in #1827 (comment), it would be helpful to describe what we expect from implementations in terms of supported combinations of ports, protocols, and listeners. It seems like the minimum bar is that L7 implementations can handle one HTTP listener on 80 and one HTTPS listener on 443.

What is less clear is what happens beyond that:

1. Is support for additional ports considered "Extended" conformance?
2. Is support for multiple listeners on the same port considered "Extended" as well?
3. What about non-standard combinations like "HTTPS" on 80 or "HTTP" on 443?

Why this is needed:
There's some variation among implementations in terms of what's supported today, it would be good to ensure expectations are clearly stated for conformance.

[shaneutt]

/help

[k8s-ci-robot]

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[dprotaso]

Is support for additional ports considered "Extended" conformance?

It would be nice if this was "Core" and didn't require unique manual configuration of each implementation to support.

Is support for multiple listeners on the same port considered "Extended" as well?

A use case here is how easy it is to manage multiple certificates on a gateway. Adding multiple listeners with the same port but different certificateRefs could be a valid option.

An alternative that scales better in K8s clusters would be #1713

What about non-standard combinations like "HTTPS" on 80 or "HTTP" on 443?

Is there a list of standard combinations?

[dprotaso]

I created a PR (#1859) that includes a conformance tests for dynamic listener ports