CoreDNS is currently a Beta feature in Kubernetes and on course to being graduated to General Availability (GA) for Kubernetes 1.11. This means that CoreDNS will be available as a standard in Kubernetes via the installation toolkits such as kubeadm, kube-up, minikube and kops.

This document will guide you to migrating the DNS service from CoreDNS to kube-dns when using the various tools available to spin up a Kubernetes cluster.

Installing CoreDNS via Kubeadm

There is an extensive guide on how to install CoreDNS instead of kube-dns via Kubeadm available here. From Kubernetes v1.10, CoreDNS supports the translation of the kube-dns ConfigMap to CoreDNS ConfigMap. That is, if you had configured stubdomains, upstreamnameservers and federation via the kube-dns ConfigMap, it will now be translated automatically to the equivalent CoreDNS ConfigMap during when choosing to install CoreDNS using kubeadm upgrade.

Stubdomain and upstreamnameserver in kube-dns translates to the proxy in CoreDNS. The federation in kube-dns has an equivalent federation in CoreDNS.

Example ConfigMap of kube-dns.

apiVersion: v1
data:
  federations: |
    {"foo" : "foo.feddomain.com"}
  stubDomains: |
    {"abc.com" : ["1.2.3.4"], "my.cluster.local" : ["2.3.4.5"]}
  upstreamNameservers: |
    ["8.8.8.8", "8.8.4.4"]
kind: ConfigMap
metadata:
  creationTimestamp: 2018-01-22T20:21:56Z
  name: kube-dns
  namespace: kube-system

CoreDNS Corefile after translation.

   .:53 {
        errors
        health
        kubernetes cluster.local  in-addr.arpa ip6.arpa {
           upstream  8.8.8.8 8.8.4.4
           pods insecure
           fallthrough in-addr.arpa ip6.arpa
        }
        federation cluster.local {
           foo foo.feddomain.com
        }
        prometheus :9153
        proxy .  8.8.8.8 8.8.4.4
        cache 30
    }
    abc.com:53 {
        errors
        cache 30
        proxy . 1.2.3.4
    }
    my.cluster.local:53 {
        errors
        cache 30
        proxy . 2.3.4.5
    }

Installing CoreDNS via Minikube.

CoreDNS is available in the addon manager and is disabled by default.

$ minikube addons list
- kube-dns: enabled
- registry: disabled
- registry-creds: disabled
- freshpod: disabled
- addon-manager: enabled
- dashboard: enabled
- coredns: disabled
- heapster: disabled
- efk: disabled
- ingress: disabled
- default-storageclass: enabled
- storage-provisioner: enabled

To enable CoreDNS, run the following command:

NOTE: Be sure to disable kube-dns after enabling CoreDNS. Otherwise, if both CoreDNS and kube-dns are running, queries may randomly hit either CoreDNS or kube-dns.

$ minikube addons enable coredns
coredns was successfully enabled

CoreDNS in kube-up

Kube-up is another way to start a Kubernetes cluster, now mostly used for deploying Kubernetes in GCE for end-to-end (e2e) testing purposes. The environment variable ENABLE_CLUSTER_DNS (default=true) is required to install DNS service. For CoreDNS can be installed as the default DNS service, the environment variable CLUSTER_DNS_CORE_DNS needs to be set to true.

CoreDNS in Kops

Currently, Kops v1.10 is set to include CoreDNS as an option to be installed instead of kube-dns. In order to install CoreDNS in place of kube-dns, we need to specify the provider as CoreDNS in the cluster yaml configuration for Kops.

spec:
  kubeDNS:
    provider: CoreDNS

This will install CoreDNS instead of kube-dns.

Installing CoreDNS via other methods

For users keen to install CoreDNS in place of kube-dns but who are not using kubeadm, minikube, kube-up, or kops, there are instructions in the CoreDNS deployment repository, which will help you to migrate from kube-dns to CoreDNS. Users should delete the kube-dns deployment after deploying CoreDNS. Otherwise, if both CoreDNS and kube-dns are running, queries may randomly hit either CoreDNS or kube-dns.