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Scenario #16
Cluster Management
K8s v1.23, self-hosted control plane
CrashLoop of Kube-Controller-Manager on Boot
Controller-manager crashed on startup due to outdated admission controller configuration.
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What Happened
After an upgrade, the --enable-admission-plugins flag included a deprecated plugin, causing crash.
Diagnosis Steps
- 1Checked pod logs in /var/log/pods/.
- 2Saw panic error: “unknown admission plugin”.
- 3Compared plugin list with K8s documentation.
Root Cause
Version mismatch between config and actual controller-manager binary.
Fix/Workaround
• Removed the deprecated plugin from startup flags.
• Restarted pod.Lessons Learned
Admission plugin deprecations are silent but fatal.
How to Avoid
- 1Track deprecations in each Kubernetes version.
- 2Automate validation of startup flags.