Make seed lease/duration configurable

[ary1992]

How to categorize this PR?

/area scalability
/kind enhancement

What this PR does / why we need it:
Make seed lease/duration period configurable.
Which issue(s) this PR fixes:
Fixes #4504

Special notes for your reviewer:

Release note:

Two fields `LeaseDurationSeconds` and `LeaseResyncSeconds` added under `SeedControllerConfiguration` to make Seed lease and duration configurable. Both field have default value of 2 seconds.

[gardener-robot]

@ary1992 Thank you for your contribution.

[gardener-robot-ci-1]

Thank you @ary1992 for your contribution. Before I can start building your PR, a member of the organization must set the required label(s) {'reviewed/ok-to-test'}. Once started, you can check the build status in the PR checks section below.

[ary1992]

/invite @shafeeqes @acumino

[BeckerMax]

/reviewed/ok-to-test

[rfranzke]

Generally, I'm wondering: Do we really need these two new fields or would one (used at both occurrences) be enough? Are there use-cases for which I'd like the .spec.leaseDurationSeconds value in the Lease object to be different compared to the duration how of the lease is renewed? Or wouldn't this rather be always equal?

[rfranzke]

Can you add a proper release note to make operators aware that this is now configurable?
Can you also extend https://github.com/gardener/gardener/blob/master/example/20-componentconfig-gardenlet.yaml and https://github.com/gardener/gardener/tree/master/charts/gardener/gardenlet accordingly, please?

[gardener-robot]

@acumino You have pull request review open invite, please check

[rfranzke]

@ary1992 The verify step is failing, can you check please?

[rfranzke]

09a0e66 looks good, thank you! Please proceed with the other improvements as discussed yesterday :)

[ary1992]

lue in the Lease object to be different compared to the duration how of the lease is renewed? Or wouldn't this rather be always equal?

Earlier two separate fields were defined as constant integer LeaseDurationSeconds and LeaseResyncSeconds. Hence two separate int variables are defined with the same name corresponding to constant integer under SeedControllerConfiguration as mentioned in issue #4504 . Moreover LeaseResyncGracePeriodSeconds was defined in terms of LeaseResyncSeconds i.e LeaseResyncGracePeriodSeconds = LeaseResyncSeconds * 10. If we can define LeaseResyncGracePeriodSeconds in terms of LeaseDurationSeconds, then one variable is enough. Need more insight on such use cases where only LeaseDurationSeconds is enough rather that two separate variables.

[rfranzke]

Need more insight on such use cases where only LeaseDurationSeconds is enough rather that two separate variables.

I would rather say the opposite: We need to know about use cases where only one configuration value is NOT enough.
@timebertt Since you originally opened the issue - do you have information about such use cases?

[rfranzke]

Thanks @ary1992, apart from the naming suggestion it looks good. I think we should go ahead with merging the two fields LeaseResyncSeconds and LeaseDurationSeconds since nobody speaks up with a justifying use-case.

[ary1992]

/merge squash

[gardener-robot]

@ary1992 You are not permitted to touch label merge/squash.

[BeckerMax]

/merge squash

[rfranzke]

It looks good, apart from the failing test I have no further comments.

[rfranzke]

/lgtm