How to configure Kube-DNS?

To configure Kube-DNS in a Kubernetes cluster, you typically follow these steps:

Check if Kube-DNS is Installed: Most Kubernetes installations come with Kube-DNS or CoreDNS by default. You can check if it's running with:
```
kubectl get pods --namespace=kube-system
```
Look for pods with names like kube-dns or coredns.
Modify the ConfigMap: If you need to change the configuration, you can modify the Kube-DNS ConfigMap. For example:
```
kubectl edit configmap kube-dns -n kube-system
```
This will open the ConfigMap in your default editor, allowing you to make changes to the DNS settings.
Add Custom DNS Records: If you want to add custom DNS records, you can do so by updating the ConfigMap. For example, you can add entries under the data section.
Restart Kube-DNS Pods: After making changes to the ConfigMap, you may need to restart the Kube-DNS pods to apply the changes:
```
kubectl delete pod -l k8s-app=kube-dns -n kube-system
```
This will force the pods to restart and pick up the new configuration.
Verify Configuration: You can verify that Kube-DNS is functioning correctly by querying DNS records from a pod:
```
kubectl run -i --tty dns-test --image=busybox --restart=Never -- sh
nslookup kubernetes.default
```

This will help you ensure that Kube-DNS is properly configured and resolving DNS queries as expected.