proposal: ablility to add clusters in PostHTTPListenerModify hook

[zirain]

I have a CRD managed by an ExtensionManager, which will create an insert HttpFilter in the HCM (think about RateLimit filter as an example).
The question is how do I manage the cluster referenced by the new filter?
Now, I can only add a cluster in the "PostTranslateModify" hook, but I can't filter only the CRDS referenced by the gateway.
I recommend enabling 'PostHTTPListenerModify' to add clusters.

WDYT? @Alice-Lilith @LiorLieberman @guydc @arkodg @zhaohuabing

[guydc]

cc @liorokman

[guydc]

I recommend enabling 'PostHTTPListenerModify' to add clusters

There's some risk here for a conflict with EG, if the cluster created by the extension server has the same "id" as a cluster that EG needs to create, if we allow extension server to create clusters before EG.

What about having a notion of user-defined backend extensions? Essentially, a CRD for defining clusters. If you control creation of listeners and clusters, you can make sure to use a consistent id.

This can even be supported in backendrefs, allowing vendors and users to build custom service discovery extensions that integrate with non-k8s service registries (consul, ... )

[zirain]

What about having a notion of user-defined backend extensions? Essentially, a CRD for defining clusters. If you control creation of listeners and clusters, you can make sure to use a consistent id.

1. another kind of Backend?
2. we may won't share clusters across listner?

This can even be supported in backendrefs, allowing vendors and users to build custom service discovery extensions that integrate with non-k8s service registries (consul, ... )

this will bring more complex than expected.