Shoot conditions lastUpdateTime is no longer updated continuously

[rfranzke]

How to categorize this PR?

/area scalability robustness
/kind enhancement
/priority normal

What this PR does / why we need it:
The shoot's .status.conditions[].lastUpdateTime is no longer continuously updated to prevent spamming etcd with too many unnecessary updates.

Special notes for your reviewer:
If the gardenlet does not renew its lease anymore then the GCM will, after a certain threshold, set the shoot conditions to Unknown to indicate that the displayed information is most likely outdated.

Release note:

The shoot's `.status.conditions[].lastUpdateTime` is no longer continuously updated. Note that if the gardenlet does not renew its lease anymore then the gardener-controller-manager will, after a certain threshold, set the `Shoot`'s conditions to `Unknown` to indicate that the displayed information is most likely outdated.

[rfranzke]

/assign @amshuman-kr @shreyas-s-rao @vlerenc

[vlerenc]

Thanks @rfranzke. When we merge it/deploy it to dev, we should check whether it indeed behaves as expected and the no longer updated .status.conditions[].lastUpdateTime will not cause trouble in the components.

WDYT if we no longer update .status.conditions[].lastUpdateTime for shoots:

• @grolu for the dashboard
• @wyb1 @mliepold for the availability monitoring

[rfranzke]

/invite @grolu @petersutter @wyb1 @mliepold

[petersutter]

we have no logic that depends on .status.conditions[].lastUpdateTime.

This would be the only effect in case it is not set (Last Updated will show nothing), however we have a PR ready to remove this field gardener/dashboard#810

[mvladev]

Btw there is already a condition builder which checks if condition really needs to be updated e.g.

gardener/pkg/gardenlet/controller/seed/seed_lease_control.go

Lines 101 to 120 in 2fb3b07

	bldr, err := helper.NewConditionBuilder(gardencorev1beta1.SeedGardenletReady)
	if err != nil {
	return err
	}
	condition := helper.GetCondition(seedCopy.Status.Conditions, gardencorev1beta1.SeedGardenletReady)
	if condition != nil {
	bldr.WithOldCondition(*condition)
	}
	bldr.WithStatus(gardencorev1beta1.ConditionTrue)
	bldr.WithReason("GardenletReady")
	bldr.WithMessage("Gardenlet is posting ready status.")
	if newCondition, update := bldr.WithNowFunc(metav1.Now).Build(); update {
	seed.Status.Conditions = helper.MergeConditions(seedCopy.Status.Conditions, newCondition)
	if err := gardenClient.Client().Status().Update(context.TODO(), seed); err != nil {
	return err
	}
	}

[amshuman-kr]

I am not aware of all the details of how these conditions and constraints are used. But looks good in principle :-)

[rfranzke]

Btw there is already a condition builder which checks if condition really needs to be updated e.g.

Yes, I know, actually I started using it, but then I faced that the botanist/health_check.go would be adapted as well, resulting in a larger refactoring. I have a WIP branch for it and will continue separately.

[vpnachev]

/lgtm

[vpnachev]

/lgtm

[mvladev]

/lgtm