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Commit 3ca8faf disabled DeleteResources (body commented out, returns nil) during the getSnapshot/putSnapshot concurrency refactor. Deletes have been silent no-ops since: resources stayed in the snapshot and delta watches never received removed_resources. Reimplement it for every resource type using the UpsertResources locking pattern (getSnapshot, Snapshot.Mu, putSnapshot, unlock, then info.mu and respondDeltaWatches). Unknown names and nodes without a snapshot are silent no-ops with no version bump. The VersionMap needs no patching because respondDeltaWatches rebuilds it via ConstructVersionMap.
…unknown type CreateDeltaWatch treated a type with no resources as nothing to answer, so a client re-subscribing with versions after the last resource was deleted parked without removed_resources. Answer whenever the client still holds versions. DeleteResources also returns early for an unknown type URL instead of indexing out of range. The no-op test now asserts a parked watch gets no response.
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📝 WalkthroughWalkthrough
ChangesDelta resource deletion
Priority: ⬇️ Low Estimated code review effort: 3 (Moderate) | ~20 minutes Change: Bug fix Suggested labels: Suggested reviewers: Merge Risk: 🟡 Moderate · up to Concurrent resource updates and deletion notifications can crash the cache. Protect SOTW response reads before merging. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches📝 Generate docstrings
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Review comments at @pkg/cache/v3/simple.go:
- Line 598: Protect the resource-map length check in CreateDeltaWatch with
Snapshot.Mu, since GetResourcesAndTTL exposes the shared Items map and
DeleteResources mutates it under the same mutex. Use the existing Snapshot.Mu
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After a control-plane restart the cache builds types one at a time. A client reconnecting with versions for a type the snapshot has never populated (nil Items) was answered with removed_resources for everything it held, so Envoy drained and re-added its listeners on every roll. respondDelta now parks such a watch until the type is set. A type emptied by deleting its last resource keeps a non-nil empty map and still reports the removal.
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🟠 Major · Notify SotW watches when DeleteResources changes the snapshot. · simple.go:611-617
pkg/cache/v3/simple.go:611-617
🎯 Functional Correctness | 🟠 Major | ⚡ Quick winNotify SotW watches when
DeleteResourceschanges the snapshot.
DeleteResourcesincrements the resource version and removes the resource, but this path calls onlyrespondDeltaWatches. A parked SotW client therefore keeps serving the deleted resource until another update or reconnect. CallrespondSOTWWatchesbeforerespondDeltaWatches, asSetSnapshotdoes.Suggested fix
info.mu.Lock() defer info.mu.Unlock() + if err := cache.respondSOTWWatches(ctx, info, snapshot); err != nil { + return err + } return cache.respondDeltaWatches(ctx, info, snapshot)🤖 Prompt for AI Agents
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Review comments at @pkg/cache/v3/simple.go:
- Around line 611-617: In DeleteResources, notify parked SotW watches after
locking info and before calling respondDeltaWatches, using the updated snapshot.
Return any error from respondSOTWWatches so delta watches are only notified if
the SotW notification succeeds.
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Also noticed (minor or nit, not blocking, not raised inline):
pkg/cache/v3/simple.go:963: CreateDeltaWatch reads the snapshot (line 963) and computesexists(line 968, the line this change edits) before it takes info.mu (line 982). If SetSnapshot or UpsertResources runs in that gap, its respondDeltaWatches pass finishes before this watch is registered. The watch is then parked (delayedResponse = !exists) even though the snapshot now has the data, and it stays unanswered until the next upsert of any type for that node. The comment at 975-981 says the 'up to date' decision and the watch registration are one atomic step. The new|| len(state.GetResourceVersions()) > 0clause closes the gap only for re-subscribers that hold versions and whose snapshot already exists. It stays open when the snapshot is nil (a reconnect before the first post-restart upsert, which creates the snapshot through SetSnapshot) and for fresh streams on an empty type. (minor)
DeleteResources only answered delta watches, so an up-to-date SOTW client parked in the shared cache kept serving a deleted cluster or listener until some other change. Respond to SOTW watches first, as SetSnapshot does.
The len() check read the Items map without Snapshot.Mu while UpsertResources and DeleteResources mutate it in place (go test -race reports it). The read also happened before info.mu, so an upsert landing in that gap answered no watch and this one then parked although the data was there. Take info.mu first and read the map under Snapshot.Mu.RLock.
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Inline comments:
Review comments at @pkg/cache/v3/simple.go:
- Around line 989-991: In the SOTW watch response path, copy the resources map
while holding `Snapshot.Mu.RLock`, then release the lock and pass the copy to
`cache.respond`. Update the `respond` closure to avoid passing the shared map
from `GetResourcesAndTTL` directly, preserving the existing version check and
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UpsertResources and DeleteResources mutate a snapshot's maps in place under Snapshot.Mu, but the SOTW paths (respondSOTWWatches, CreateWatch, Fetch, heartbeats) read the version and iterate the map without it. DeleteResources now calls respondSOTWWatches, so a concurrent upsert on the same node could overlap that iteration (go test -race reports it). Read the version and copy the map under Mu.RLock in one helper and respond from the copy.
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Summary
snapshotCache.DeleteResourceshas been a silent no-op since commit 3ca8faf (2025-01-16, "Concurrency"). That refactor moved the cache togetSnapshot/putSnapshotand a per-snapshotMu. The old ClusterType-only body was commented out instead of being ported, and the function returns nil.xlr8 publishes
deleteevents when a service config, port or subset goes away, and when a gateway route stops referencing a backend. All of them have been dropped, so removed clusters stay in the snapshot and in Envoy until the proxy reconnects. We confirmed this live:real-time-dispatcher/defaultcluster is on 62/62 zone-b waypoints connected to older xlr8 replicas, and on 0/8 connected to younger ones.Changes
DeleteResourcesis restored for all resource types.UpsertResources:getSnapshot,Snapshot.Mu, delete the items, bump the type version,putSnapshot, unlock, theninfo.muandrespondDeltaWatches.VersionMapneeds no patching, becauserespondDeltaWatches/CreateDeltaWatchrebuild it throughConstructVersionMap.CreateDeltaWatchreports the removal of a type's last resource.existsrequired the type to be non-empty. So if the last resource was deleted while the stream had no parked watch, a re-subscribing client with that version in its state got a parked watch and never receivedremoved_resources.existsnow also holds when the client state has versions.respondDeltastill sends only when there are resources or removals, so there are no empty responses. A fresh stream on an empty type still parks.8f5c8a59f,768484b33, tagv0.12.0-v3.2.3-beta.24).beta.23): after an xlr8 restart the cache fills one type at a time (CDS first). A reconnecting Envoy's LDS request carries the listener version it holds; the CDS-only snapshot has no LDS items, soCreateDeltaWatchansweredremoved=[listener]. LDS was re-added moments later, so every gateway drained and re-added its listener on every xlr8 roll (seen live on the shadow gateway).respondDeltanow returns no response when the snapshot's map for the type is nil (never populated) and the client holds versions, so the watch stays parked until the type is set. The check sits inrespondDelta, so therespondDeltaWatchespath (an upsert of another type re-checking parked watches) is covered too.DeleteResourcesleaves a non-nil empty map.beta.24left gatewaylistener_added/removed/modified,cluster_added/removedand listenerlast_updatedunchanged.Tests (
pkg/cache/v3/delete_resources_test.go)Each test failed against the old code first.
RemovedResources == ["b"].go test -race ./pkg/cache/v3/... -count=1: no data races and no new failures. 13 tests fail identically onnexus(e47cc846b), for exampleTestDeltaRemoveResourcesandTestSnapshotCacheDeltaWatchfailing with "failed to get resource version". Those fixtures build resources without aVersion, andConstructVersionMaprejects that. This PR does not touch that.Rollout note
This makes removals real fleet-wide after 8+ months of no-ops. The xlr8 side, a separate PR, gates delete events behind
XDS_DELETE_MODE=off|log|on(defaultlog), so we can audit what would be removed in preprod before turning deletes on. Please don't tag a release consumed by xlr8 prod until that xlr8 change lands.Semantics differing from upstream
A caller that builds a full snapshot with
SetSnapshotand omits a type to mean "none of this type" no longer triggers removals for clients holding that type; they stay parked. Pass the type with an empty slice to mean empty. xlr8 only usesUpsertResources/BatchUpsertResources/DeleteResources, so it is unaffected.Known gap (follow-up in xlr8)
If a node's last resource of a type is deleted while xlr8 is down, the reconnecting client is not told to remove it: xlr8 never writes an empty type for a node whose generation returns nothing. Planned xlr8 fix: upsert an empty map when a full wildcard generation succeeds with zero resources.
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