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kubernetes-the-hard-way/docs/12-dns-addon.md
Frank Messier 3f90202f03 Amend output of the get pods command 
Still somewhat of a k8s n00b, so sorry if I'm out of line here, but I'd like to propose a small amendment to the output of the get pods command confirming the deployment of the kube-dns add-on. 

This seems like a deployment creating a single replicaset by default, the output should then list a single RS.

From the deployment's YAML file:
spec:
  # replicas: not specified here:
  # 1. In order to make Addon Manager do not reconcile this replicas parameter.
  # 2. Default is 1.
  # 3. Will be tuned in real time if DNS horizontal auto-scaling is turned on.

Output of a describe of the resulting deployment:

kubectl describe deployment kube-dns -n kube-system | grep ReplicaSet
OldReplicaSets:  <none>
NewReplicaSet:   kube-dns-6c857864fb (1/1 replicas created)
2017-12-20 21:53:04 -05:00

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Deploying the DNS Cluster Add-on

In this lab you will deploy the DNS add-on 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

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