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 --filename ./manifests/coredns-1.10.1.yaml

output

serviceaccount/coredns created
clusterrole.rbac.authorization.k8s.io/system:coredns created
clusterrolebinding.rbac.authorization.k8s.io/system:coredns created
configmap/coredns created
service/kube-dns created
deployment.apps/coredns created

List the pods created by the kube-dns deployment:

kubectl get pods --namespace kube-system --selector k8s-app=kube-dns

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 pod:

kubectl run busybox --image busybox:1.36.1 --command -- sleep infinity

List the pod created:

kubectl get pods --selector 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 --selector run=busybox \
  --output jsonpath="{.items[0].metadata.name}")

Execute a DNS lookup for the kubernetes service inside the busybox pod:

kubectl exec --stdin --tty "${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

Delete the busybox pod:

kubectl delete pod "${POD_NAME}"

Next: Smoke Test