External DNS Not Resolving After Cluster Network Changes

External DNS resolution stopped working after changes were made to the cluster network configuration.

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What Happened

After modifying the CNI configuration and reconfiguring IP ranges, external DNS resolution failed for services outside the cluster.

Diagnosis Steps

1Checked DNS resolution inside the cluster using kubectl exec and found that internal DNS queries were working, but external queries were failing.
2Verified DNS resolver configuration and noticed that the external DNS forwarders were misconfigured after network changes.

Root Cause

The external DNS forwarder settings were not correctly updated after network changes.

Fix/Workaround

• Updated CoreDNS configuration to correctly forward DNS queries to external DNS servers.
• Restarted CoreDNS pods to apply changes.

Lessons Learned

Network configuration changes can impact DNS settings, and these should be verified post-change.

How to Avoid

1Implement automated DNS validation tests to ensure external DNS resolution works after network changes.
2Document and verify DNS configurations before and after network changes.