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.