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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, backed by CoreDNS, to applications running inside the Kubernetes cluster.

The DNS Cluster Add-on

Deploy the coredns cluster add-on:

Note that if you have changed the service CIDR range and thus this file, you will need to save your copy onto master-1 (paste to vi, then save) and apply that.

kubectl apply -f https://raw.githubusercontent.com/mmumshad/kubernetes-the-hard-way/master/deployments/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

NAME                       READY   STATUS    RESTARTS   AGE
coredns-699f8ddd77-94qv9   1/1     Running   0          20s
coredns-699f8ddd77-gtcgb   1/1     Running   0          20s

Reference: https://kubernetes.io/docs/tasks/administer-cluster/coredns/#installing-coredns

Verification

Create a busybox pod:

kubectl run busybox --image=busybox:1.28 --command -- sleep 3600

List the pod created by the busybox pod:

kubectl get pods -l run=busybox

output

NAME                      READY   STATUS    RESTARTS   AGE
busybox-bd8fb7cbd-vflm9   1/1     Running   0          10s

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

kubectl exec -ti busybox -- nslookup kubernetes

output

Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      kubernetes
Address 1: 10.96.0.1 kubernetes.default.svc.cluster.local

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