DNS Debugging

Debugging DNS issues in Kubernetes can be a complex task due to the distributed nature of the system. Here are some common steps you might take:

  1. Check the DNS Service: Ensure that the DNS service is running correctly in your cluster. You can use the kubectl get services command to check the status of the service.

  2. Check DNS Endpoints: Use the kubectl get endpoints kube-dns --namespace=kube-system command to check the endpoints of the DNS service.

  3. Check DNS Pods: Ensure that the DNS pods are running correctly. You can use the kubectl get pods --namespace=kube-system command to check the status of the pods.

  4. Check DNS Configuration: Check the configuration of your DNS service. The configuration file is typically located at /etc/resolv.conf on each of your nodes.

  5. Test DNS Resolution: You can test DNS resolution within your cluster by creating a simple pod and using the nslookup command to query the DNS service.

  6. Check Network Policies: If you’re using network policies, ensure that they’re not blocking DNS traffic.

  7. Check Logs: Check the logs of your DNS pods for any error messages or warnings. You can use the kubectl logs command to view the logs.

Remember, these are just general steps and the exact debugging process can vary depending on your specific setup and the nature of the issue.

DNS Utils

DNS Utils is a useful tool in Kubernetes for debugging DNS related issues. It’s essentially a prepackaged set of tools installed in a pod that you can use to investigate DNS problems.

To use DNS Utils in Kubernetes, you can create a pod that uses the dnsutils image. This image includes a variety of tools such as dig, nslookup, and host that can be used to probe and investigate DNS issues.

Here’s an example of how you can create a DNS Utils pod:

apiVersion: v1
kind: Pod
metadata:
  name: dnsutils
  namespace: default
spec:
  containers:
  - name: dnsutils
    image: k8s.gcr.io/e2e-test-images/jessie-dnsutils:1.3
    command:
      - sleep
      - "3600"
    imagePullPolicy: IfNotPresent
  restartPolicy: Always

Execute the following command:

kubectl apply -f dnsutils.yaml

kubectl get pods dnsutils
NAME      READY     STATUS    RESTARTS   AGE
dnsutils   1/1       Running   0          <some-time>

Once that Pod is running, you can exec nslookup in that environment. If you see something like the following, DNS is working correctly.

kubectl exec -i -t dnsutils -- nslookup kubernetes.default
Server:    10.0.0.10
Address 1: 10.0.0.10
 
Name:      kubernetes.default
Address 1: 10.0.0.1

To read more about this debugging pod please follow the official Kubernetes documentation.