Pod DNS Resolution Failure Due to CoreDNS Configuration Issue

DNS resolution failures occurred within pods due to a misconfiguration in the CoreDNS config map.

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What Happened

CoreDNS was misconfigured to not forward DNS queries to external DNS servers, causing pods to fail when resolving services outside the cluster.

Diagnosis Steps

1Ran kubectl exec in the affected pods and verified DNS resolution failure.
2Inspected the CoreDNS ConfigMap and found that the forward section was missing the external DNS servers.

Root Cause

CoreDNS was not configured to forward external queries, leading to DNS resolution failure for non-cluster services.

Fix/Workaround

• Updated the CoreDNS ConfigMap to add the missing external DNS server configuration.
• Restarted the CoreDNS pods to apply the changes.

Lessons Learned

Always review and test DNS configurations in CoreDNS, especially for hybrid clusters.

How to Avoid