Resolve HA / multi-thread concerns around Gateway updates

[knative-extensions]

Resolve HA / multi-thread concerns around Gateway updates

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/lifecycle stale

[github-actions]

This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
inactivity. Reopen the issue with /reopen. Mark the issue as
fresh by adding the comment /remove-lifecycle stale.

[evankanderson]

/remove-lifecycle stale

I'll take a look and see if this is still necessary

[dprotaso]

Sorta a dupe of #363

Two potential options to explore:

1. From kubernetes-sigs/gateway-api#1248 - add a conformance test to assert Gateway merges and push for this to be part of the CORE.
2. See if Server side apply gives us some granularity here - maybe we use distinct field managers for listener entries - though this implies there isn't some validation preventing duplicate listeners (which is trying to be added via kubernetes-sigs/gateway-api#847) which I'm trying to halt - kubernetes-sigs/gateway-api#847 (comment) (ignore as hostname would be unique in each listener)

Related to 1. I think we should formalize a different way of merging Gateways beyond having the same addresses. I'll make a GEP for this.

[dprotaso]

Upstream GEP issue
kubernetes-sigs/gateway-api#1713

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This issue is stale because it has been open for 90 days with no
activity. It will automatically close after 30 more days of
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[ReToCode]

/remove-lifecycle stale
/triage accepted

[dprotaso]

An alternative as well is using server side apply -

I've added the client API here - kubernetes-sigs/gateway-api#2537

It'll need more exploration once the client changes land