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Using CoreDNS for Service Discovery
This page describes the CoreDNS upgrade process and how to install CoreDNS instead of kube-dns.
Before you begin
You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. It is recommended to run this tutorial on a cluster with at least two nodes that are not acting as control plane hosts. If you do not already have a cluster, you can create one by using minikube or you can use one of these Kubernetes playgrounds:
You can use CoreDNS instead of kube-dns in your cluster by replacing kube-dns in an existing deployment, or by using tools like kubeadm that will deploy and upgrade the cluster for you.
For manual deployment or replacement of kube-dns, see the documentation at the CoreDNS GitHub project.
Migrating to CoreDNS
Upgrading an existing cluster with kubeadm
In Kubernetes version 1.10 and later, you can also move to CoreDNS when you use
kubeadm to upgrade
a cluster that is using
kube-dns. In this case,
kubeadm will generate the CoreDNS configuration
("Corefile") based upon the
kube-dns ConfigMap, preserving configurations for
stub domains, and upstream name server.
If you are moving from kube-dns to CoreDNS, make sure to set the
CoreDNS feature gate to
during an upgrade. For example, here is what a
v1.11.0 upgrade would look like:
kubeadm upgrade apply v1.11.0 --feature-gates=CoreDNS=true
In Kubernetes version 1.13 and later the
CoreDNS feature gate is removed and CoreDNS
is used by default.
In versions prior to 1.11 the Corefile will be overwritten by the one created during upgrade. You should save your existing ConfigMap if you have customized it. You may re-apply your customizations after the new ConfigMap is up and running.
If you are running CoreDNS in Kubernetes version 1.11 and later, during upgrade, your existing Corefile will be retained.
In Kubernetes version 1.21, support for
kube-dns is removed from kubeadm.
CoreDNS is available in Kubernetes since v1.9. You can check the version of CoreDNS shipped with Kubernetes and the changes made to CoreDNS here.
CoreDNS can be upgraded manually in case you want to only upgrade CoreDNS or use your own custom image. There is a helpful guideline and walkthrough available to ensure a smooth upgrade.
When resource utilisation is a concern, it may be useful to tune the configuration of CoreDNS. For more details, check out the documentation on scaling CoreDNS.