kubernetes-the-hard-way/docs/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

Deploy the coredns cluster add-on:

kubectl apply -f ./deployments/coredns-1.9.3.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.apps/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-8494f9c688-hh7r2   1/1     Running   0          10s
coredns-8494f9c688-zqrj2   1/1     Running   0          10s

Verification

Create a busybox deployment:

kubectl run 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