Add Support for EndpointSlices

[robscott]

/area networking
/kind feature

Describe the feature

It would be great if Knative could support EndpointSlices. This is a new Kubernetes resource that provides a scalable and extensible alternative to Endpoints. Although there may be more cases where this pattern is used, I've noticed that Knative manually creates Endpoints in some cases. With the EndpointSliceProxying feature gate enabled, kube-proxy will read exclusively from EndpointSlices, unfortunately disregarding any Endpoints without any corresponding EndpointSlices and effectively breaking parts of Knative. I've been the main developer for this feature in Kubernetes and I'm happy to answer any questions or help anyone that's interesting in adding support for this.

/cc @Cynocracy

[tcnghia]

cc @vagababov @markusthoemmes

[vagababov]

/assign

It's quite interesting that this was the exact question I asked in Barcelona during the presentation of the API (what will happen to the APIs that manually create endpoints) and it was completely ignored by the presenters :-)

[vagababov]

Now to the actual problem at hand, @robscott ,
do we basically have to create both endpoints and endpointslices mirroring the contents?

[robscott]

@vagababov Yep, that's what would be needed. We're also looking into ways we can mirror custom Endpoints to EndpointSlices automatically, but any automatic approach will be imperfect. As an example, EndpointSlices have topology fields that can't be derived from Endpoints resources. On the other hand, if you're not interested in anything specific with EndpointSlices, this potential automatic mirroring approach may suffice. I'll follow up here with more details as I have them.

[vagababov]

Yeah, I am not sure we have any use for topology just yet. Might be interesting in future with NLS work or to pick activators from the same zone as nodes, etc, but right now, just copy of IP addresses.

[markusthoemmes]

I wondered about this too, especially looking at #7260. We could have a more efficient solution there, not relying on subset ordering in the endpoints object if we had an endpointslice just for the activator IPs potentially.

It's only beta in 1.17 though, what's the availability of the API currently?

[robscott]

The API itself is enabled by default in 1.17, the controller is enabled by default in 1.18, and kube-proxy is not configured to use EndpointSlices by default yet in any version. For now this will only come up for users that intentionally enable the EndpointSliceProxying feature gate in 1.18 or EndpointSlice in feature gate on kube-proxy in 1.16-1.17. As I've looked into this further, it looks like we should be able to solve this issue automatically with some kind of mirroring in 1.19 (before this feature is enabled by default).

It may be worth adding some kind of note in the documentation here that Knative is currently incompatible with the EndpointSliceProxying feature gate. I'll also be updating EndpointSlice docs to note the issue, and hope to have a more automatic mirroring solution in place for 1.19. I'm happy to close this issue for now as well since it sounds like you actually shouldn't need to do anything for EndpointSlice integration.

[vagababov]

Let's keep it anyway, even if no integration will be required anyway. Since as Markus noted we might have some interesting usages for slices ourselves.

[vagababov]

Thanks for the help, Rob.

[robscott]

Quick update on this feature. A new EndpointSliceMirroring controller has been added as part of the 1.19 release and along with that kube-proxy now reads from EndpointSlices on Linux by default.