In our previous post, we showed how CoreDNS can be used in place of Kube-DNS for service discovery in Kubernetes clusters. In that blog, there is a footnote about issues trying to replace Kube-DNS when using Google Container Engine (GKE). As it so happens, there is a similar issue with minikube, which is a local Kubernetes environment that is very useful for developers.
When you try to replace Kube-DNS, you will find that shortly after you modify its service to point to CoreDNS, your changes will be reverted. This is because Minikube has an addon manager that periodically verifies the configuration state of any installed addons, and Kube-DNS is one of those addons.
Luckily, this is really easy to solve for Minikube. The minikube command allows you to modify the installed
plugins for Minikube. So, we simply need to disable the kube-dns addon before running our kubectl apply -f
that is described in the previous blog:
$ minikube addons list
- dashboard: enabled
- default-storageclass: enabled
- kube-dns: enabled
- heapster: disabled
- ingress: disabled
- registry-creds: disabled
- addon-manager: enabled
$ minikube addons disable kube-dns
kube-dns was successfully disabled
$ minikube addons list
- heapster: disabled
- ingress: disabled
- registry-creds: disabled
- addon-manager: enabled
- dashboard: enabled
- default-storageclass: enabled
- kube-dns: disabled
Now we can apply the coredns.yaml, and also delete the kube-dns ReplicationController which
will not be automatically deleted by disabling the addon.
$ kubectl apply -f coredns.yaml
serviceaccount "coredns" configured
clusterrole "system:coredns" configured
clusterrolebinding "system:coredns" configured
configmap "coredns" configured
deployment "coredns" configured
service "kube-dns" configured
$ kubectl get -n kube-system pods
NAME READY STATUS RESTARTS AGE
coredns-980047985-g2748 1/1 Running 1 36m
kube-addon-manager-minikube 1/1 Running 0 9d
kube-dns-v20-qzvr2 3/3 Running 0 1m
kubernetes-dashboard-ks1jp 1/1 Running 0 9d
$ kubectl delete -n kube-system rc kube-dns-v20
replicationcontroller "kube-dns-v20" deleted
$
And there we have it, CoreDNS is up and running and won’t be overwritten by the addon manager.