Even lighter weight CRD-only API Server? about kcp HOT 8 CLOSED

@detiber and I chatted briefly but he's out on PTO for a bit so it might get delayed. I was going to create a stub investigation in docs/investigations for "minimal kube-apiserver as reusable embeddable library" and then we can do some prep with folks over next few weeks. Sound good?

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Ok, the stub is merged. When Jason is back we'll try to tee up a community meeting / round table where we go over use cases. In the meantime, I need to accumulate some of the historical efforts at this within Kube for reference.

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Thanks for your feedback! I haven't dug into those projects, but I'm definitely excited to learn more.

The badidea example is even more stripped down; CRDs seemingly must be cluster-scoped, presumably because there's no such thing as a namespace 😆 -- and RBAC support seems necessary to be able to do anything useful with it with 2+ users. From the "what's missing" slide in the api-machinery presentation, it looks like badidea + what's-missing ~= kcp, so I think we're just circling roughly the same final state. That's really encouraging validation for the idea, honestly.

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Would be happy to chat more about this, FWIW.

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Yeah I don't think there is anything special about the types that are baked in still, other than you might actually want efficient high scale rbac / namespaces (a few other objects). Agree from a "reusable bits perspective" you want "can serve APIs" to be a bit that has some layers on top of it like "can subdivide and feel like a regular cluster". It should be possible to let the layering be natural

import (
  "k8s.io/apiserver/pkg/basic"
  "k8s.io/apiserver/pkg/apisets/core"
)

func main() {
  // simple
  api := basic.New()
  api.AllowCRDs()
  // less simple
  // i want to get namespaces!
  api.AddGroups(core.New())
  // specialized
  api.RegisterClusterScopedAdmission(&myImplementationOfConceptsUnderneathClusters{})
  // everyone starts the same
  api.Serve()
}

or whatever (massively oversimplified) to get different use cases and allow library-like composability.

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@detiber and I chatted briefly but he's out on PTO for a bit so it might get delayed. I was going to create a stub investigation in docs/investigations for "minimal kube-apiserver as reusable embeddable library" and then we can do some prep with folks over next few weeks. Sound good?

SGTM!

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Created a stub in #74 which we can iterate on over time.

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I've finally been able to find a little bit of time to explore this a bit further today (only actually ran kcp now).

main...vorburger:kcp-core-minimal is a first quick hack simply removing ~50 lines + imports re. if installClusterController {. What's dumb (of me), of course, is that so far I've just copy/pasted everything else.. still ~60 lines for the etcd, certs et al. set-up. Where may we move that to, for avoiding that copy/paste? And then evolve that into something like a POC of the API that Clayton outlined above... Could that, for now, move e.g. to kcp/pkg/kcp? I'm not quite sure yet how to best go about the next step.

PS: I probably can't make #96 tomorrow, but I'll try to start listening in for coming weeks, time permitting.

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