Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage #123935

serathius · 2024-03-14T14:31:52Z

/kind bug

With discovery of etcd watch correctness under the extreme cases of watch congestion (#123072 (comment)), #123532 is no longer a sufficient mitigation.

Even with watch cache protected, direct watches to etcd will still suffer loss of events and cause etcd memory blot. Rolling forward with improvements to etcd watch like etcd-io/etcd#17555 might be more riskly as will cause watch compaction affect new code paths.

Serving watches directly from etcd was reintroduced in 1.27 as a simple correctness fix #115096, however we didn't anticipate such big impact on stability and correctness of watch.

I propose to revert the #115096 and leave a WatchFromStorageWithoutResourceVersion feature flag to get the old behavior. At least for as long we implement ConsistentWatchFromCache as part of KEP-2340

kube-apiserver: fixes a 1.27+ regression in watch stability by serving watch requests without a resourceVersion from the watch cache by default, as in <1.27 (disabling the change in #115096 by default). This mitigates the impact of an etcd watch bug (https://github.com/etcd-io/etcd/pull/17555). If the 1.27 change in #115096 to serve these requests from underlying storage is still desired despite the impact on watch stability, it can be re-enabled with a `WatchFromStorageWithoutResourceVersion` feature gate.

staging/src/k8s.io/apiserver/pkg/features/kube_features.go

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher_whitebox_test.go

dims · 2024-03-14T14:55:56Z

@serathius @liggitt we want this in 1.30 and backports all the way back to 1.27 right?

dims · 2024-03-14T14:56:20Z

/priority critical-urgent

dims · 2024-03-14T14:56:35Z

/sig etcd

liggitt · 2024-03-14T14:58:18Z

@serathius @liggitt we want this in 1.30 and backports all the way back to 1.27 right?

yup :-/

staging/src/k8s.io/apiserver/pkg/features/kube_features.go

serathius · 2024-03-17T12:26:06Z

/retest

serathius · 2024-03-17T14:08:31Z

Yey! Got through test issues! cc @liggitt

Note; I have updated getWatchCacheResourceVersion and it's test to make sure it passes and treated TestWatchSemantics test as authoritative to Watch behavior.

wojtek-t · 2024-03-18T08:57:15Z

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

 func (c *Cacher) getWatchCacheResourceVersion(ctx context.Context, parsedWatchResourceVersion uint64, opts storage.ListOptions) (uint64, error) {
 	if len(opts.ResourceVersion) != 0 {
 		return parsedWatchResourceVersion, nil
 	}
+	// legacy case
+	if !utilfeature.DefaultFeatureGate.Enabled(features.WatchFromStorageWithoutResourceVersion) && opts.SendInitialEvents == nil && opts.ResourceVersion == "" {


Why do we add it here?

If we're already at this point, we will be serving watch from cache. So the problem we're facing [being watches on etcd overloading etcd] is not a problem here. I don't think this is needed here - I would revert changes to this function.

The refactors for WatchList have changed the default behavior of watch cache, that was not a problem was previously this response was served from etcd, however to pass the tests (WatchSemantics and conformance test) I need to update this function.

Reason is that getWatchCacheResourceVersion returns a ResourceVersion to which the watch cache must be synchronized to. Without this change getWatchCacheResourceVersion will call GetCurrentResourceVersionFromStorage which is meant for consistent read, and wait for such revision.

With my change I will return zero, which means serve the data available from cache, which is consistent with the old behavior.

OK - we will need to update tests when we will switch FG default, but that's fine.

So the tests should effectively be [if FG set, then 100, otherwise 0].
So maybe please add a short comment for those tests that when we switch FG, those should be reverted to 100.

Added the comment.

I have a hard time following what this bit does, but at least the 1.27 / 1.28 / 1.29 backports won't need this and will be a straight gating of the etcd pass-through, right?

yes - this bit will not be part of backports

wojtek-t · 2024-03-18T08:59:22Z

/hold

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher.go

…romStorageWithoutResourceVersion feature gate to allow serving watch from storage.

wojtek-t · 2024-03-18T11:00:36Z

/lgtm
/approve

/hold cancel

k8s-ci-robot · 2024-03-18T11:00:43Z

LGTM label has been added.

Git tree hash: 1ee9a24abc8f29c9648098950fee946f000bcadb

k8s-ci-robot · 2024-03-18T11:00:55Z

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hzxuzhonghu, liggitt, serathius, wojtek-t

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Needs approval from an approver in each of these files:

~~pkg/features/OWNERS~~ [liggitt,wojtek-t]
~~staging/src/k8s.io/apiserver/pkg/features/OWNERS~~ [liggitt,wojtek-t]
~~staging/src/k8s.io/apiserver/pkg/storage/OWNERS~~ [liggitt,wojtek-t]

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serathius · 2024-03-18T12:03:21Z

/retest

liggitt · 2024-03-19T11:54:06Z

staging/src/k8s.io/apiserver/pkg/storage/cacher/cacher_test.go

+		defer featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, features.WatchFromStorageWithoutResourceVersion, false)()
+		store, terminate := testSetupWithEtcdAndCreateWrapper(t)
+		t.Cleanup(terminate)
+		storagetesting.RunWatchSemantics(context.TODO(), t, store)


I think this doubling of the RunWatchSemantics test is responsible for the increased timeout rate in https://testgrid.k8s.io/sig-release-master-blocking#ci-kubernetes-unit&width=20 and #123850

…1.29 Cherry-pick of #120897 #123935 #123887 #123994: Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage.

…1.28 Cherry-pick of #123935: Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage.

…1.27 Cherry-pick of #123935: Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage.

serathius force-pushed the consistent-watch-from-etcd branch from a89f73c to e74151b Compare March 14, 2024 14:32

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k8s-ci-robot requested review from hzxuzhonghu and MadhavJivrajani March 14, 2024 14:37

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serathius force-pushed the consistent-watch-from-etcd branch from c586bca to 206b10f Compare March 14, 2024 14:58

serathius changed the title ~~Allow escape hatch to disable direct watches to etcd~~ Introduce a ConsistentWatchFromStorage feature gate, enabled by default, that can be used to disable direct watches to etcd Mar 14, 2024

serathius force-pushed the consistent-watch-from-etcd branch from 206b10f to c13ddd4 Compare March 14, 2024 15:03

serathius changed the title ~~Introduce a ConsistentWatchFromStorage feature gate, enabled by default, that can be used to disable direct watches to etcd~~ Introduce a WatchFromCacheWithoutResourceVersion feature gate, that can be used to disable direct watches to storage. Mar 14, 2024

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Serve watch without resourceVersion from cache and introduce a WatchF…

0130072

…romStorageWithoutResourceVersion feature gate to allow serving watch from storage.

serathius force-pushed the consistent-watch-from-etcd branch from efb2abd to 0130072 Compare March 18, 2024 10:55

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serathius mentioned this pull request Mar 18, 2024

Cherry-pick of #120897 #123935 #123887 #123994: Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage. #123973

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p0lyn0mial mentioned this pull request Mar 19, 2024

[Flaking Test] UT k8s.io/apiserver/pkg/storage cacher #123850

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tooptoop4 mentioned this pull request Apr 11, 2024

Controller: invalid config map object received in config watcher. Ignored processing with CPU spike argoproj/argo-workflows#11657

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Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage #123935

Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage #123935

serathius commented Mar 14, 2024 •

edited by liggitt

dims commented Mar 14, 2024

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liggitt Mar 19, 2024 •

edited

Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage #123935

Serve watch without resourceVersion from cache and introduce a WatchFromStorageWithoutResourceVersion feature gate to allow serving watch from storage #123935

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serathius commented Mar 14, 2024 • edited by liggitt

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