Issue: Starting with GKE version 1.36, the default engine for kube-dns is CoreDNS.

Starting with GKE version 1.36, the default engine for kube-dns is CoreDNS. For Pod IP DNS queries in the <a-b-c-d>.<namespace>.pod.cluster.local format, CoreDNS returns NXDOMAIN if the specified <namespace> does not exist. The legacy kubernetes/dns implementation skipped checking the existence of the namespace provided in the <namespace> segment in these queries.

Queries in the <a-b-c-d>.<namespace>.pod.cluster.local format are not part of the Kubernetes DNS specification. We can't guarantee that uses outside of those specified in the DNS spec will remain consistent across releases.

Mitigation:

• Recommended: Migrate to supported headless Service DNS records (<hostname>.<subdomain>.<namespace>.svc.cluster.local). • Workaround: Ensure the <namespace> specified in the DNS query exists in the cluster.