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DNS not resolving in cluster or from pod

Service name fails, external DNS wrong, or CoreDNS unhealthy.

Reviewed: ·Tested on: Kubernetes 1.29, Terraform 1.8, Ubuntu 22.04

Symptoms

  • Could not resolve host from inside pod
  • Intermittent NXDOMAIN for cluster services
  • External DNS points to wrong IP

1Test from a debug pod

kubectl run dnscheck --rm -it --image=busybox:1.36 --restart=Never -- nslookup kubernetes.default
kubectl run dnscheck --rm -it --image=busybox:1.36 --restart=Never -- nslookup <service>.<ns>.svc.cluster.local
DNS debug snippet →

2Check CoreDNS

kubectl get pods -n kube-system -l k8s-app=kube-dns
kubectl logs -n kube-system -l k8s-app=kube-dns --tail=50
kubectl get configmap coredns -n kube-system -o yaml

3Ingress / external DNS

dig app.example.com +short
kubectl get ingress -n <ns>
# compare ingress ADDRESS to dig result
Network debug hub →

Related

kubernetesdnsnginxbind9k8s-deployment-service