Scenario

Frontend pod frontend-app cannot connect to Backend pod backend-app using the service name http://backend-svc. It returns “Name or service not known”.

Question

How do you debug this DNS/Network issue?

Expected Answer

1. Verify Service: Does backend-svc exist? Does it have valid Endpoints? (kubectl get ep backend-svc). If no endpoints, the selector doesn’t match the pods.
2. Test DNS: Exec into frontend pod and run nslookup backend-svc or dig backend-svc.default.svc.cluster.local.
3. Check CoreDNS: Are CoreDNS pods running in kube-system? Check their logs for errors.
4. Network Policy: Is there a NetworkPolicy blocking traffic between these namespaces/pods?