[release-3.6] Add write-only-skip-check option for --v2-deprecation to bypass the v2 content check

[sahilpatel09]

Takes over #21250

I saw #21848 PR to my understanding it was closed due to it targeting the main and AssertNoV2StoreContent has already been removed

I have backported it to 3.6 with the changes from #21250

While reproducing locally with no snapshot I saw these errors for WAL check due to 3.6 replaying v2 WAL entries and panics.

{"level":"panic","ts":"2026-05-29T10:03:47.719549-0400","caller":"schedule/schedule.go:202","msg":"execute job failed","job":"server_applyAll","panic":"detected disallowed v2 WAL for stage --v2-deprecation=write-only","stacktrace":"go.etcd.io/etcd/pkg/v3/schedule.(*fifo).executeJob.func1\n\tgo.etcd.io/etcd/pkg/v3@v3.6.11/schedule/schedule.go:202\nruntime.gopanic\n\truntime/panic.go:783\ngo.uber.org/zap/zapcore.CheckWriteAction.OnWrite\n\tgo.uber.org/zap@v1.27.0/zapcore/entry.go:196\ngo.uber.org/zap/zapcore.(*CheckedEntry).Write\n\tgo.uber.org/zap@v1.27.0/zapcore/entry.go:262\ngo.uber.org/zap.(*Logger).Panic\n\tgo.uber.org/zap@v1.27.0/logger.go:285\ngo.etcd.io/etcd/server/v3/etcdserver.v2ToV3Request\n\tgo.etcd.io/etcd/server/v3/etcdserver/apply_v2.go:31\ngo.etcd.io/etcd/server/v3/etcdserver.(*EtcdServer).applyEntryNormal\n\tgo.etcd.io/etcd/server/v3/etcdserver/server.go:1983\ngo.etcd.io/etcd/server/v3/etcdserver.(*EtcdServer).apply\n\tgo.etcd.io/etcd/server/v3/etcdserver/server.go:1924\ngo.etcd.io/etcd/server/v3/etcdserver.(*EtcdServer).applyEntries\n\tgo.etcd.io/etcd/server/v3/etcdserver/server.go:1210\ngo.etcd.io/etcd/server/v3/etcdserver.(*EtcdServer).applyAll\n\tgo.etcd.io/etcd/server/v3/etcdserver/server.go:985\ngo.etcd.io/etcd/server/v3/etcdserver.(*EtcdServer).run.func6\n\tgo.etcd.io/etcd/server/v3/etcdserver/server.go:855\ngo.etcd.io/etcd/pkg/v3/schedule.job.Do\n\tgo.etcd.io/etcd/pkg/v3@v3.6.11/schedule/schedule.go:41\ngo.etcd.io/etcd/pkg/v3/schedule.(*fifo).executeJob\n\tgo.etcd.io/etcd/pkg/v3@v3.6.11/schedule/schedule.go:206\ngo.etcd.io/etcd/pkg/v3/schedule.(*fifo).run\n\tgo.etcd.io/etcd/pkg/v3@v3.6.11/schedule/schedule.go:187"}
panic: detected disallowed v2 WAL for stage --v2-deprecation=write-only [recovered]
        panic: execute job failed

I did not include any changes for this as it is beyond the scope of original PR but open to a discussion to implement it.

[k8s-ci-robot]

Hi @sahilpatel09. Thanks for your PR.

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[sahilpatel09]

/cc @ahrtr

[ahrtr]

I saw #21848 PR to my understanding it was closed due to it targeting the main and AssertNoV2StoreContent has already been removed

We still need #21848, otherwise when users upgrade from 3.6 to 3.7, it may break.

[ahrtr]

pls squash commits.

[ahrtr]

/ok-to-test

[ahrtr]

Pls update this PR per ahrtr@3d12fea, which I manually verified.

[codecov]

Codecov Report

❌ Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 68.81%. Comparing base (8b95963) to head (4233958).

Files with missing lines	Patch %	Lines
server/storage/util.go	0.00%	3 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
server/config/v2_deprecation.go	92.30% <100.00%> (ø)
server/etcdmain/config.go	76.08% <100.00%> (+0.26%)	⬆️
server/storage/util.go	76.54% <0.00%> (-2.95%)	⬇️

... and 24 files with indirect coverage changes

@@               Coverage Diff               @@
##           release-3.6   #21850      +/-   ##
===============================================
- Coverage        68.92%   68.81%   -0.12%     
===============================================
  Files              420      420              
  Lines            35868    35873       +5     
===============================================
- Hits             24722    24685      -37     
- Misses            9699     9735      +36     
- Partials          1447     1453       +6     

---

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[ahrtr]

cc @fuweid @serathius

[ahrtr]

pls add an item

'write-only-skip-check'  // Custom v2 state is not allowed similar to 'write-only', but bypass the v2 content check. WARNING: Users should read the 3.5 -> 3.6 upgrade guide and use this option at their own risk.

right after 'write-only'

etcd/server/etcdmain/help.go

Line 175 in 8b95963

'write-only' // Custom v2 state is not allowed (default in v3.6)

[ahrtr]

We missed this change in 3.6.12, let's get it included in 3.6.13. cc @fuweid @ivanvc @serathius

[fuweid]

LGTM

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, fuweid, sahilpatel09

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[ahrtr]

can you add a changelog item under https://github.com/etcd-io/etcd/blob/main/CHANGELOG/CHANGELOG-3.6.md#etcd-server? thx