DNS Resolution Failure After Cluster Upgrade

DNS resolution failures occurred across pods after a Kubernetes cluster upgrade.

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What Happened

After upgrading the Kubernetes cluster, DNS resolution stopped working for certain namespaces, causing intermittent application failures.

Diagnosis Steps

1Checked CoreDNS logs and found no errors, but DNS queries were timing out.
2Verified that the upgrade process had updated the CoreDNS deployment, but the config map was not updated correctly.

Root Cause

Misconfiguration in the CoreDNS config map after the cluster upgrade.

Fix/Workaround

• Updated the CoreDNS config map to the correct version.
• Restarted CoreDNS pods to apply the updated config.

Lessons Learned

After upgrading the cluster, always validate the configuration of critical components like CoreDNS.

How to Avoid

1Automate the validation of key configurations after an upgrade.
2Implement pre-upgrade checks to ensure compatibility with existing configurations.