fix: replace a pod its StatefulSet can no longer replace - #410
fix: replace a pod its StatefulSet can no longer replace#410melancholictheory wants to merge 2 commits into
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Node StatefulSets use OrderedReady pod management, and under that policy the StatefulSet controller performs no update work until the existing pod is Running and Ready. A pod that never becomes Ready is therefore the one thing blocking its own replacement: correcting the spec updates the template and the revision, and the pod stays on the superseded revision indefinitely, leaving the cluster in Reconciling until someone deletes the pod by hand. The node controller now deletes a pod that is both not ready and on a revision the StatefulSet has already superseded. A pod crash-looping on the revision the StatefulSet still wants is left alone: recreating it yields the same pod and the same crash, which would turn a visible configuration error into an endless restart loop. Deleting pods needs a verb the operator did not have, so the pods RBAC rule gains delete in both controllers. Closes valkey-io#408 Signed-off-by: melancholictheory <selimvhorst@gmail.com>
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Included review availability: Your plan provides up to 2 included reviews per hour; 1 remains after this review. 📝 WalkthroughWalkthroughThe ValkeyNode controller detects stuck pods from superseded StatefulSet revisions and deletes them after synchronization. RBAC grants pod deletion. Tests cover ownership and revision checks. Documentation defines the emitted event. ChangesSuperseded pod recovery
Sequence Diagram(s)sequenceDiagram
participant ValkeyNodeController
participant KubernetesAPI
participant StatefulSetPod
ValkeyNodeController->>KubernetesAPI: Synchronize StatefulSet without a pod roll
ValkeyNodeController->>KubernetesAPI: Fetch node pod
ValkeyNodeController->>StatefulSetPod: Check ownership, revision, and readiness
ValkeyNodeController->>KubernetesAPI: Delete superseded pod
ValkeyNodeController->>ValkeyNodeController: Emit SupersededPodDeleted
Suggested reviewers: Merge Risk: 🟡 Moderate · up to The PR automatically deletes stuck superseded Pods, but the current implementation could delete a replacement Pod during a narrow race and grants the operator authority to delete Pods across the cluster. Merge should wait for explicit acceptance or mitigation of these bounded reliability and security risks. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Linked Issues checkExplanation The changes address issue
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Inline comments:
In `@internal/controller/valkeynode_controller.go`:
- Around line 906-909: Update the pod-deletion decision around podIsReady so it
reads controller-revision-hash first and returns false when the revision is
empty; retain the existing StatefulSet revision comparison and unready-pod
behavior for observed revisions. Add a regression case covering an unready pod
with no revision label.
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config/rbac/role.yamldocs/status-conditions.mdinternal/controller/valkeycluster_controller.gointernal/controller/valkeynode_controller.gointernal/controller/workload_roll_test.go
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| if err := r.replaceSupersededPod(ctx, node, sts); err != nil { | ||
| return err | ||
| } | ||
| return r.clearWorkloadRollPending(ctx, node) |
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After replaceSupersededPod requests deletion of an obsolete unready Pod, this branch immediately clears WorkloadRollPending. The StatefulSet controller has not yet created, much less made Ready, the replacement Pod, so a parent rollout coordinator can advance while this node's workload remains unavailable. Have the deletion helper report that it initiated replacement and requeue without clearing the pending condition; clear it only after the replacement workload has converged.
Artifacts
PR #410 superseded Pod validation source
- Temporary executable Go validation source exercises the changed reconciler decision predicates and API-client flow, with the takeaway that the target path was executed directly.
PR #410 superseded Pod reconciliation capture
- Runs the changed reconciler and shows intended deletion plus immediate pending-state clearing and deletion of an unowned label-matching Pod, establishing both failures.
| // Both halves of the check matter. A pod crash-looping on the revision the | ||
| // StatefulSet still wants is left alone, because recreating it yields the same | ||
| // pod and the same crash, which would turn a visible configuration error into | ||
| // an endless restart loop. |
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getPod selects Pods by ValkeyNode labels, and a missing controller-revision-hash compares unequal to UpdateRevision. An unowned, unready Pod that merely shares those labels can therefore be selected and deleted by this controller. Select the expected StatefulSet Pod deterministically and verify its controller owner reference matches the managed StatefulSet before deleting it; also require a non-empty revision label before treating a Pod as superseded.
Artifacts
PR #410 superseded Pod validation source
- Temporary executable Go validation source exercises the changed reconciler decision predicates and API-client flow, with the takeaway that the target path was executed directly.
PR #410 superseded Pod reconciliation capture
- Runs the changed reconciler and shows intended deletion plus immediate pending-state clearing and deletion of an unowned label-matching Pod, establishing both failures.
Two hardening cases from review. getPod selects on labels alone, so a pod that merely carries the node's labels could be picked up and deleted. The predicate now requires the StatefulSet being reconciled to be the pod's controller, matched on kind, name and UID. A pod without a controller-revision-hash compared unequal to a non-empty UpdateRevision and so read as superseded. A pod the StatefulSet has not stamped yet cannot be judged against a revision, so an empty label now returns false rather than qualifying for deletion. Signed-off-by: melancholictheory <selimvhorst@gmail.com>
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Two of the three review points were right and are fixed in 95d5af6. The third does not hold, and I would rather say why than quietly leave it. Ownership before deletion. Correct, and it was the one worth catching. {"kind": "StatefulSet", "name": "valkey-rolltest-0-1",
"uid": "986cd8d8-f342-41e8-b19d-38eec4cd3a02", "controller": true}A pod with no revision label. Also correct. An empty Clearing Re-verified on k3d after the change, since an ownership check is exactly the kind of thing that can quietly turn a working fix into a no-op. Same reproduction as before: the wedge heals on its own, pod replaced, cluster back to Ready in about 30 seconds, one |
| if err := r.replaceSupersededPod(ctx, node, sts); err != nil { | ||
| return err | ||
| } | ||
| return r.clearWorkloadRollPending(ctx, node) |
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After replaceSupersededPod deletes an obsolete unready Pod, this branch immediately clears WorkloadRollPending. The replacement Pod has not yet been created or made Ready, while the prior Ready=true status can remain visible. The cluster controller can therefore treat this node as settled and advance its one-at-a-time rollout while the node is unavailable. Keep the pending condition until the replacement workload has converged.
Artifacts
Targeted Go harness source for pending-roll timing
- Captured the exact Go test source that creates the old unready Pod, invokes the StatefulSet reconciliation path, and evaluates parent advancement; it isolates the timing defect.
Expected safe gate assertion fails before the current behavior is accepted
- Ran the harness requiring WorkloadRollPending to remain through replacement readiness; it failed with pending=false and no replacement Pod, proving the safe expectation is violated.
Observed current reconcile behavior and parent advancement
- Ran the harness accepting current behavior; it passed and recorded pending=false, oldPodExists=false, replacementPodExists=false, nodeReady=true, and parentResult=0, proving the parent can advance in the gap.
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Coming back to this one, because the reasoning got sharper and deserves a straight answer rather than a repeat of mine.
The new argument drops the WorkloadRollPending reader and rests on Ready staying visibly true after the deletion. That cannot happen here, and the reason is in the precondition rather than in the timing.
A pod only qualifies as superseded when the StatefulSet's revision has moved past it. It only stays on the old revision because OrderedReady refuses to replace a pod that is not Ready. So "superseded and not ready" implies the pod was already not Ready before the revision advanced, which means updateStatus had already written Ready=False well before replaceSupersededPod could look at it. There is no settled state for the cluster controller to act on.
Measured rather than argued, on the same k3d reproduction: during the wedge and before any deletion the node reads False/PodNotReady, and polling once a second through the whole replacement gave 75 samples with no point where Ready was true while the pod was absent. Ready went False to True only once the replacement was running. One-second sampling cannot rule out a sub-second window, which is why the precondition argument above is the one I would lean on.
I suspect the harness reached nodeReady=true by constructing it, setting a ready status next to an unready pod. The real status path does not produce that pair.
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You're right. I overstated the finding, and the harness result was testing an impossible status/pod combination rather than the production status path.
For the wedge this PR addresses, podSupersededAndStuck can only match after the pod was already unready. updateStatus records Ready=False for that pod, and its isWorkloadRolledOut gate also prevents Ready=True while the StatefulSet revisions differ. replaceSupersededPod then runs before the subsequent status refresh, but it does not turn that recorded Ready=False back into true; clearing WorkloadRollPending therefore cannot make the cluster controller advance based on a settled node in this path.
The separate status patches do leave a theoretical stale-status race if pod readiness changes before the node controller observes it, but that is not the deterministic issue I raised, and the measured reproduction supports your argument. I’m withdrawing this comment; it should not block the PR.
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This PR closes #408
Summary
Node StatefulSets use
OrderedReadypod management, and under that policy the StatefulSet controller performs no update work until the existing pod is Running and Ready. A pod that never becomes Ready is therefore the one thing blocking its own replacement: correcting the spec updates the template and the revision, the pod stays on the superseded revision, and the cluster sits inReconcilinguntil someone deletes the pod by hand.The node controller now deletes that pod itself.
Features / Behaviour Changes
A node whose pod is not ready and is left on a revision the StatefulSet has already superseded gets that pod deleted, so the corrected template takes effect without manual intervention. The deletion emits a
SupersededPodDeletedevent on theValkeyNode.Deleting pods needs a verb the operator did not have, so the
podsRBAC rule gainsdeletein both controllers.Implementation
The decision is a small pure predicate,
podSupersededAndStuck, and it is worth reading with the second half in mind rather than the first:Both halves matter. A pod crash-looping on the revision the StatefulSet still wants is deliberately left alone. Recreating it produces the same pod and the same crash, so the operator would be running its own restart loop on top of kubelet's, and a configuration error that is visible today as
CrashLoopBackOffwould instead churn pods forever. Only a pod that a newer revision has already superseded is deleted, because for that one the replacement the user asked for exists and the pod is the only thing in its way.@bjosv pointed at Strimzi and the Zalando postgres-operator on #357, which both restart stuck pods. This is the same idea with a narrower trigger, for that reason.
The call sits in the branch of
ensureStatefulSetthat runs when the StatefulSet already matches the desired template, which is exactly the state the wedge leaves behind: the operator considers its work done and the pod is still on the old revision. Both facts the predicate needs are already at hand, so there is no new watch and no extra round trip. Pods are in the cache (cmd/main.goselects them byapp.kubernetes.io/managed-by), the node controller already lists them throughgetPod, and the StatefulSet is read on the same path.podIsReadyis extracted from the inline loop thatupdateStatusalready had, so readiness has one definition.Limitations
Only StatefulSet workloads. Deployments replace pods through ReplicaSets and do not have the
OrderedReadygate, so they do not wedge this way.The pod is deleted on the reconcile after the template update, once
sts.Status.UpdateRevisionreflects the new revision. In practice that is the next pass.Testing
TestPodSupersededAndStuckcovers the predicate: stuck on a superseded revision, crash-looping on the current revision, ready on a superseded revision, already terminating, no revision observed yet, and nil inputs.Verified on k3d with the operator built from this branch, on a 3 shard cluster with 1 replica each.
Bad image, which is the reproduction from #408: setting
spec.imagetovalkey/valkey:8.1.1wedges a replica onFATAL CONFIG FILE ERROR. Reverting tovalkey/valkey:9.0.0used to sit unchanged for the seven minutes I watched it. The pod is now replaced on its own, UID65d2c5cato1c8e1f2c, and the cluster is back to Ready in about 30 seconds.Broken exporter args, which is the reproduction from #357: same wedge, and removing the bad arg heals it in about 30 seconds without touching the pod.
The case that must not act: leaving the broken exporter arg in place, so the pod crash-loops on the revision the StatefulSet still wants. The pod UID did not change over three minutes and no deletion was emitted. Across all of it there were exactly two
SupersededPodDeletedevents, one per genuine heal.Two pre-existing failures are unrelated to this change and reproduce identically on a clean
upstream/main: theshould surface resize progress when the PVC is still expandingandshould surface resize failures when the PVC cannot expand furtherspecs, 138 passed and 2 failed either way.Checklist
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