Reduce apiserver lease duration and GC interval to 20s

[carreter]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Reduces apiserver lease duration and garbage collection interval from 1 hour to 20 seconds (twice the lease renewal interval). This allows for faster detection of whether an apiserver is unhealthy, as its lease will expire much more quickly if it is not being actively renewed.

Allows other services to use apiserver leases as a reliable way of determining the number of available apiservers. Current specific use-case is for konnectivity-network-proxy agents to dynamically determine the number of k8s apiservers (and thus proxy servers assuming a 1:1 apiserver:proxy server mapping, which is usually the case). See this issue and this design doc for more information.

Which issue(s) this PR fixes:

N/A

Special notes for your reviewer:

N/A

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

- [KNP dynamic proxy server count scaling design doc]: https://docs.google.com/document/d/16G8U-QWR4tNfY2jiOk-ZUEMVwBkq9R9iXZqXrxPsGOE/edit#heading=h.ymlc40jj6ff0

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: carreter
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[aojea]

/ok-to-test
/assign @wojtek-t @andrewsykim

any implications for scalability?
do we foresee we'll need to be able to define custom values?

[cici37]

/assign @jpbetz @deads2k Since it looks like a big change.
/triage accepted

[carreter]

As a heads up, after some discussion it's been decided that konnectivity-network-proxy will be rolling its own lease controller and not depending on the apiserver leases. I'd imagine that reducing this duration would still be useful for other situations in which an up-to-date count of apiservers is necessary.

EDIT: GKE will still end up going the apiserver lease route, though the plan is still to extend KNP to include the lease controller.

[carreter]

Giving this a bump. To answer @aojea 's questions to the best of my ability:

any implications for scalability?

This does add a non-trivial number of requests to the k8s apiserver, as leases will have to be renewed every 10secs rather than every hour. I believe this is worth the cost in order to maintain an up-to-date count of the identities and status of the apiservers.

do we foresee we'll need to be able to define custom values?

I don't think so. Assuming the cost incurred of having a relatively short lease duration is acceptable, it seems to me that there would be no need to increase it again.

[deads2k]

/hold

The choice of a long time for this lease was intentional, not accidental. We chose a long duration because the consequences of apiserver identity being improperly reaped are severe enough to cause malfunctioning of core capability like LISTing CRs, namespace deletion, and garbage collection. See the reasoning here: https://github.com/kubernetes/enhancements/tree/master/keps/sig-api-machinery/1965-kube-apiserver-identity#caveats

While there might be some appetite for making this configurable, a skim of the intent here appears to be to use this lease in a manner similar to an endpoint slice. That sort of usage needs to account for the various readyz, healthz, livez checks. While this may appear to be similar, it is a building block for very different usage related to apiserver coordination on storage versions.

[carreter]

Closing this issue as we have opted to use a custom lease controller to manage KNP leases rather than depend on the apiserver leases given the issues raised by @deads2k. Thanks for the feedback everyone!