[WIP] KEP-3926: show how we address client cache inconsistency issue #4949
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tkashem
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Nov 5, 2024
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| A client backed up an informer already has the object in its cache, since the | ||
| client never receives a `watch.DELETED` event the object remains in the lsiter | ||
| cache. This creates an inconsistency - retrieving the object from the cache | ||
| yields the object, but if we get it from the storage we see a `corrupt object` | ||
| error. |
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Based on the proposed solution, this means that all existing clients will remain in a corrupted state indefinitely without the ability to recover. To have a safe rollout for our own clients (not even considering external clients yet), this means we need to promote handling for this special error to locked-to-true status until every supported kubelet (n-3) has the value locked-to-true before we can start enabling the server-side capability. Otherwise we can end up with unrecoverable corruption, correct?
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| A client backed up by an informer already has the object in its cache, since the | ||
| client never receives a `watch.DELETED` event the object remains in the lsiter | ||
| cache. This creates an inconsistency - retrieving the object from the cache |
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Not sure I can parse the sentence. You are saying the cache will be stuck?
| the old cache be replaced. | ||
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| - Pros: the existing clients will work without any code change | ||
| - Cons: relisting is expensive |
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I think this is acceptable for the situation of a single object being unsafely deleted. Wondering, for the usecase of a lost encryption key, aren't we confronted with potentially many objects? Each will cause a relist 🤔
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In the whole discussion about downsides of the approaches, wondering about the alternative of doing a manual delete directly through etcd. Where are we with that today? How does the apiserver and clients (reflector) behave in that case?
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I believe manually deleting the etcd key directly will have the same effect, etcd will relay the delete event to any client watching for it.
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In other words: we don't regress even if we need a client change? That is crucial IMO and should be documented.
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Rereading your option description: A does not need that client change. And your implementation PR kubernetes/kubernetes#127513 has no client-go changes (beyond the added test).
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| yields the object, but if we get it from the storage we see a `corrupt object` | ||
| error. | ||
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| There are a few factors we need to consider to understan how the client is impacted: |
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| There are a few factors we need to consider to understan how the client is impacted: | |
| There are a few factors we need to consider to understand how the client is impacted: |
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