（Kubernetes）watch chan error: etcdserver: mvcc: required revision has been compactedというエラー

APIサーバに定期的に出る

ログを見るとこんな感じで定期的に出てきます。

W0301 08:23:56.457841       1 watcher.go:229] watch chan error: etcdserver: mvcc: required revision has been compacted
W0301 08:31:36.434391       1 watcher.go:229] watch chan error: etcdserver: mvcc: required revision has been compacted
W0301 08:46:48.806759       1 watcher.go:229] watch chan error: etcdserver: mvcc: required revision has been compacted
W0301 09:01:23.817826       1 watcher.go:229] watch chan error: etcdserver: mvcc: required revision has been compacted

このメッセージはetcdが持っている履歴の圧縮を行う処理関連に見てます。

実際、この圧縮はAPIサーバがetcdに司令を投げていますが、特に設定を入れずともデフォルトで以下のように圧縮がかかっているように見えます。

{"level":"info","ts":"2022-03-01T22:56:16.280Z","caller":"mvcc/index.go:214","msg":"compact tree index","revision":4324643}
{"level":"info","ts":"2022-03-01T22:56:16.282Z","caller":"mvcc/kvstore_compaction.go:57","msg":"finished scheduled compaction","compact-revision":4324643,"took":"1.114364ms"}
{"level":"info","ts":"2022-03-01T23:01:16.318Z","caller":"mvcc/index.go:214","msg":"compact tree index","revision":4325041}
{"level":"info","ts":"2022-03-01T23:01:16.321Z","caller":"mvcc/kvstore_compaction.go:57","msg":"finished scheduled compaction","compact-revision":4325041,"took":"1.495808ms"}

結論：正常なので無視してOK

Openshiftでも同事象は起きているようで以下のスレッドがあがっていましたが

 openshift-apiserver pod has lots of spam logs "E0331...etcdserver: mvcc: required revision has been compacted"

やり取りとしてはバグなので無視してOK・・とのこと。

実際にetcd側を見ても正常に圧縮がかかっているようにも見えています。もちろんクラスターの状況も問題なし。

# kubectl get cs
Warning: v1 ComponentStatus is deprecated in v1.19+
NAME                 STATUS    MESSAGE                         ERROR
etcd-0               Healthy   {"health":"true","reason":""}
controller-manager   Healthy   ok
scheduler            Healthy   ok

というわけでerrorといいつつも特に気にしなくても良さそう。