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Scenario #23
Cluster Management
K8s v1.23, managed GKE

CoreDNS CrashLoop Due to Invalid ConfigMap Update

CoreDNS stopped resolving names cluster-wide after a config update.

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What Happened

A platform engineer edited the CoreDNS ConfigMap to add a rewrite rule, but introduced a syntax error. The new pods started crashing, and DNS resolution stopped working across the cluster.

Diagnosis Steps
  • 1Ran kubectl logs -n kube-system -l k8s-app=kube-dns – saw config parse errors.
  • 2Used kubectl describe pod to confirm CrashLoopBackOff.
  • 3Validated config against CoreDNS docs.
Root Cause

Invalid configuration line in CoreDNS ConfigMap.

Fix/Workaround
• Rolled back to previous working ConfigMap.
• Restarted CoreDNS pods to pick up change.
Lessons Learned

ConfigMap changes can instantly affect cluster-wide services.

How to Avoid
  • 1Use coredns -conf <file> locally to validate changes.
  • 2Test changes in a non-prod namespace before rollout.
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