12-dns-addon.md

Deploying the DNS Cluster Add-on

In this lab you will deploy the DNS add-on which provides DNS based service discovery, backed by CoreDNS, to applications running inside the Kubernetes cluster.

The DNS Cluster Add-on

Get the CoreDNS yaml:

wget https://storage.googleapis.com/kubernetes-the-hard-way/coredns-1.8.yaml

Edit the coredns.yaml file to change CoreDNS configuration to enable DNS resolution for external name:

sed '/.*prometheus :9153/a \ \ \ \ \ \ \ \ forward . /etc/resolv.conf' coredns.yaml

Deploy the coredns cluster add-on:

kubectl apply -f 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 (you may need to wait a few seconds to see the pods "READY"):

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 (you may need to wait a few seconds to see the pod "READY"):

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