Consistently propagate down timeouts from MD => MS => Machines

[sbueringer]

Goal

Goal of this issue is to consistently propagate down timeouts (NodeDrainTimeout, NodeDeletionTimeout, ...) from MDs to MSs to Machines. This is desirable so that users can still change timeouts even if a Machine is e.g. stuck in draining.

We had a first PR which ensures a MachineSet propagates down the timeouts to Machines which are in deleting: #10589

But there are a few other cases, as described here: #10589 (inlining below for convenience)

The following specifically focuses on cases where Machines are deleted by the MS controller.

Case 1. MD is deleted

The following happens:

• MD goes away
• ownerRef triggers MS deletion
• MS goes away
• ownerRef triggers Machine deletion

=> The MS will already be gone when the deletionTimestamp is set on the Machines. In this case folks would have to modify the timestamps on each Machine individually. Because the MS doesn't exist anymore it's not possible to propagate down timeouts from the MS to Machines

Case 2. MD is scaled down to 0

The following happens:

• MD scales down MS to 0
• MS deletes Machine

This use case was addressed by: #10589

Case 3. MD rollout

The following happens:

• Someone updates the MD (e.g. bump the Kubernetes version)
• MD creates a new MS and scales it up
• In parallel MD scales down the old MS to 0

=> In this scenario today the MD controller does not propagate the timeouts from MD to all MS (only to the new/current one, not to the old ones). So the Machines of the old MS won't get new timeouts set in the MD

Implementation

To address all scenarios I would propose to always propagate timeouts from MD => MS => Machine. To make that happen we have to implement the following:

• Ensure during MD deletion, MD & MS objects stay around until all Machines are deleted: Consider implementing "forced" MD foreground deletion #10710
  • PR: 🌱 Foreground deletion for machine deployments #10791
• Ensure timeouts are always propagated from MD to all MachineSets to all Machines
  • Even if a MD, MS or Machine is in deleting (also both in regular reconcile & reconcileDelete)
  • Even if a MS is not the "current" MS

Follow-up:

• We should also check other objects like Cluster (topology), KCP, ...

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[sbueringer]

@enxebre @fabriziopandini @chrischdi @vincepri
Would be good if you can double check if I missed something and if my proposed implementation a) solves the entire problem b) sounds good to you.

[vincepri]

So the Machines of the old MS won't get new timeouts set in the MD

Isn't this a good default behavior? Ideally, if a MachineSet is stuck in deleting, I should be able to change only that specific one without impacting the new one?

[sbueringer]

Good question. Timeouts today don't trigger a rollout (i.e. a new MS) and also don't trigger a separate revision.

Might be annoying to have to manually go to the MS and update the timeouts there when you otherwise primarily/only interact with the MD

[sbueringer]

Maybe one important point to consider. Going forward we won't have old MachineSets that stay around forever. All of them will be in "scaling down" until they are gone (once we dropped revision management).

So I think our only goal for them is to properly scale them down. There probably is no reason that they have to preserve their previous timeout configuration

[enxebre]

The proposed steps sgtm Stefan.

Isn't this a good default behavior? Ideally, if a MachineSet is stuck in deleting, I should be able to change only that specific one without impacting the new one?

I think it would be suboptimal UX for the use cases where MachineDeloyment is the consumer facing API to force user interaction with the machineSets that are still managed by it.

[vincepri]

(once we dropped revision management).

I missed this part, what are we doing for rollbacks?

[vincepri]

Found #10479 — which I wasn't aware of, and I guess now this issue makes a bit more sense to me on the reasoning 😄