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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 to applications running inside the Kubernetes cluster.
+
+## The DNS Cluster Add-on
+
+Deploy the `kube-dns` cluster add-on:
+
+```
+kubectl create -f https://storage.googleapis.com/kubernetes-the-hard-way/kube-dns.yaml
+```
+
+> output
+
+```
+serviceaccount "kube-dns" created
+configmap "kube-dns" created
+service "kube-dns" created
+deployment "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
+kube-dns-3097350089-gq015   3/3       Running   0          20s
+kube-dns-3097350089-q64qc   3/3       Running   0          20s
+```
+
+## Verification
+
+Create a `busybox` deployment:
+
+```
+kubectl run busybox --image=busybox --command -- sleep 3600
+```
+
+List the pod created by the `busybox` deployment:
+
+```
+kubectl get pods -l run=busybox
+```
+
+> output
+
+```
+NAME                       READY     STATUS    RESTARTS   AGE
+busybox-2125412808-mt2vb   1/1       Running   0          15s
+```
+
+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)