kubernetes-the-hard-way/docs/12-dns-addon.md

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# Deploying the DNS Cluster Add-on
In this lab you will deploy the [DNS add-on](https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/) which provides DNS based service discovery, backed by [CoreDNS](https://coredns.io/), to applications running inside the Kubernetes cluster.
## The DNS Cluster Add-on
Deploy the `coredns` cluster add-on on `controller-0`:
```
kubectl apply -f https://storage.googleapis.com/kubernetes-the-hard-way/coredns.yaml
```
> output
```
serviceaccount/coredns created
clusterrole.rbac.authorization.k8s.io/system:coredns created
clusterrolebinding.rbac.authorization.k8s.io/system:coredns created
configmap/coredns created
deployment.extensions/coredns created
service/kube-dns created
```
List the pods created by the `kube-dns` deployment:
```
kubectl get pods -l k8s-app=kube-dns -n kube-system
```
> output
```
NAME READY STATUS RESTARTS AGE
coredns-699f8ddd77-94qv9 1/1 Running 0 20s
coredns-699f8ddd77-gtcgb 1/1 Running 0 20s
```
## Verification
Create a `busybox` deployment:
```
kubectl run --generator=run-pod/v1 busybox --image=busybox:1.28 --command -- sleep 3600
```
List the pod created by the `busybox` deployment:
```
kubectl get pods -l run=busybox
```
> output
```
NAME READY STATUS RESTARTS AGE
busybox 1/1 Running 0 3s
```
Retrieve the full name of the `busybox` pod:
```
POD_NAME=$(kubectl get pods -l run=busybox -o jsonpath="{.items[0].metadata.name}")
```
Execute a DNS lookup for the `kubernetes` service inside the `busybox` pod:
```
kubectl exec -ti $POD_NAME -- nslookup kubernetes
```
> output
```
Server: 10.32.0.10
Address 1: 10.32.0.10 kube-dns.kube-system.svc.cluster.local
Name: kubernetes
Address 1: 10.32.0.1 kubernetes.default.svc.cluster.local
```
Next: [Smoke Test](13-smoke-test.md)