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12-dns-addon.md

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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 coredns cluster add-on:

kubectl create -f https://storage.googleapis.com/kubernetes-the-hard-way/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.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-589fff4ffc-6k6h4   1/1     Running   0          22s
coredns-589fff4ffc-cqjsg   1/1     Running   0          22s

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

Upstream resolution

To enable upstream DNS resolution just download and modify the coredns.yaml int the Corefile section as follows:

  Corefile: |
    .:53 {
        errors
        health
        ready
        kubernetes cluster.local in-addr.arpa ip6.arpa {
          pods insecure
          upstream
          fallthrough in-addr.arpa ip6.arpa
        }
        forward . 8.8.8.8
        prometheus :9153
        cache 30
        loop
        reload
        loadbalance
    }
---

Next: Smoke Test