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fix: serialize SecurityGroup ingress reconciles per SecurityGroup - #4890

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madvocate:issue-4889
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fix: serialize SecurityGroup ingress reconciles per SecurityGroup#4890
madvocate wants to merge 1 commit into
kubernetes-sigs:mainfrom
madvocate:issue-4889

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@madvocate madvocate commented Aug 29, 2026 •
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#4889

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  • Added tests that cover your change (if possible)
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  • Backfilled missing tests for code in same general area 🎉
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@kubernetes-prow kubernetes-prow Bot added the do-not-merge/invalid-commit-message Indicates that a PR should not merge because it has an invalid commit message. label Aug 29, 2026
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[APPROVALNOTIFIER] This PR is NOT APPROVED

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  • ✅ login: madvocate / name: Marek Suscak (b5b430b)

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@kubernetes-prow kubernetes-prow Bot added needs-ok-to-test Indicates a PR that requires an org member to verify it is safe to test. cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. labels Aug 29, 2026
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Hi @madvocate. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work.

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@kubernetes-prow kubernetes-prow Bot added size/L Denotes a PR that changes 100-499 lines, ignoring generated files. cncf-cla: yes Indicates the PR's author has signed the CNCF CLA. and removed cncf-cla: no Indicates the PR's author has not signed the CNCF CLA. labels Aug 29, 2026
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serialize SecurityGroup ingress reconciles per SecurityGroup
d3b3cbf 
Concurrent reconciles of the same SecurityGroup each perform a
non-atomic read-modify-write sequence: fetch the current rules, diff
them against the desired permissions, then authorize/revoke. When two
reconciles interleave, one can diff against a snapshot taken while the
other was mid-mutation and revoke rules without granting replacements,
leaving the SecurityGroup without any of the controller-managed rules.

With the shared backend SecurityGroup feature this removes every
ALB-to-target ingress rule on the cluster SecurityGroup at once,
failing health checks and client traffic for all load balancers until
the deferred TargetGroupBinding reconciler restores the rules (~30
minutes after a controller restart).

Observed in production during Fargate maintenance: endpoint churn on
the TargetGroupBinding defining the aggregated port-range boundary
produced two concurrent reconciles; CloudTrail shows the controller
authorizing tcp/3000-3008, revoking tcp/3000-8025, then 45 seconds
later revoking tcp/3000-3008 again with no replacement grant.

Serialize ReconcileIngress per SecurityGroup ID with a keyed mutex held
across the fetch and the mutations, so every reconcile diffs against
post-mutation state. Reconciles of different SecurityGroups are not
serialized against each other.
@kubernetes-prow kubernetes-prow Bot removed the do-not-merge/invalid-commit-message Indicates that a PR should not merge because it has an invalid commit message. label Sep 1, 2026
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