Troubleshoot Kubernetes DNS¶

Introduction¶

This guide explains troubleshoot kubernetes dns with practical kubectl commands, realistic output, and production-focused checks. Kubernetes networking issues usually involve selectors, endpoints, ports, DNS, ingress rules, CNI behavior, or NetworkPolicy.

When You Need This¶

Use this guide when pods are running but traffic does not reach them, DNS names do not resolve, ingress returns errors, or service endpoints are missing.

Example Configuration¶

apiVersion: apps/v1
kind: Deployment
metadata:
  name: web
  namespace: app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: web
  template:
    metadata:
      labels:
        app: web
    spec:
      containers:
      - name: web
        image: nginx:1.27
        ports:
        - containerPort: 80

Step-by-Step Checks¶

kubectl get pods -n kube-system -l k8s-app=kube-dns
kubectl logs -n kube-system deployment/coredns
kubectl run dns-test --rm -it --image=busybox:1.36 --restart=Never -- nslookup kubernetes.default
kubectl get events -n app --sort-by=.lastTimestamp
kubectl get events -n app --sort-by=.lastTimestamp

Expected output:

NAME                         READY   STATUS    RESTARTS   AGE
coredns-7db6d8ff4d-abcde     1/1     Running   0          3d

Verification¶

kubectl get endpoints web -n app
kubectl run curl --rm -it --image=curlimages/curl --restart=Never -- curl -I http://web.app.svc.cluster.local

Troubleshooting¶

Verify that service selectors match pod labels, targetPort matches the container port, endpoints exist, DNS resolves, and NetworkPolicy allows the traffic path.

Common Mistakes¶

• Creating a Service whose selector does not match any pod labels.
• Confusing port, targetPort, nodePort, and containerPort.
• Testing ingress before confirming the service works inside the cluster.

Quick Checklist¶

• Check pod labels.
• Check service selector and endpoints.
• Test DNS inside the cluster.
• Test service before ingress.
• Review NetworkPolicy and ingress-controller logs.

Related Guides¶

• Troubleshoot Service Not Working
• Network Policy Explained
• kubectl Port Forward

Summary¶

Kubernetes networking is easier when you test inside out: pod, service endpoint, DNS, policy, ingress, then external traffic.