# Using CoreDNS for Service Discovery

LLMS index: [llms.txt](/llms.txt)

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This page describes the CoreDNS upgrade process and how to install CoreDNS instead of kube-dns.


## Before you begin

<p>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
<a href="https://minikube.sigs.k8s.io/docs/tutorials/multi_node/">minikube</a>
or you can use one of these Kubernetes playgrounds:</p>
<ul>
<li><a href="https://labs.iximiuz.com/playgrounds?category=kubernetes&filter=all">iximiuz Labs</a></li>
<li><a href="https://killercoda.com/playgrounds/scenario/kubernetes">Killercoda</a></li>
<li><a href="https://kodekloud.com/public-playgrounds">KodeKloud</a></li>
</ul>
 
 
 Your Kubernetes server must be at or later than version v1.9.
  <p>To check the version, enter  <code>kubectl version</code>.</p>



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## About CoreDNS

[CoreDNS](https://coredns.io) is a flexible, extensible DNS server
that can serve as the Kubernetes cluster DNS.
Like Kubernetes, the CoreDNS project is hosted by the
<a class='glossary-tooltip' title='Cloud Native Computing Foundation' data-bs-toggle='tooltip' data-bs-placement='top' href='https://cncf.io/' target='_blank' aria-label='CNCF'>CNCF</a>.

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.

## Installing CoreDNS

For manual deployment or replacement of kube-dns, see the documentation at the
[CoreDNS website](https://coredns.io/manual/installation/).

## Migrating to CoreDNS

### Upgrading an existing cluster with kubeadm

In Kubernetes version 1.21, kubeadm removed its support for `kube-dns` as a DNS application.
For `kubeadm` v1.36, the only supported cluster DNS application
is CoreDNS.

You can move to CoreDNS when you use `kubeadm` to upgrade a cluster that is
using `kube-dns`. In this case, `kubeadm` generates the CoreDNS configuration
("Corefile") based upon the `kube-dns` ConfigMap, preserving configurations for
stub domains, and upstream name server.

## Upgrading CoreDNS

You can check the version of CoreDNS that kubeadm installs for each version of
Kubernetes in the page
[CoreDNS version in Kubernetes](https://github.com/coredns/deployment/blob/master/kubernetes/CoreDNS-k8s_version.md).

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](https://github.com/coredns/deployment/blob/master/kubernetes/Upgrading_CoreDNS.md)
available to ensure a smooth upgrade.
Make sure the existing CoreDNS configuration ("Corefile") is retained when
upgrading your cluster.

If you are upgrading your cluster using the `kubeadm` tool, `kubeadm`
can take care of retaining the existing CoreDNS configuration automatically.


## Tuning CoreDNS

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](https://github.com/coredns/deployment/blob/master/kubernetes/Scaling_CoreDNS.md).

## What's next

You can configure [CoreDNS](https://coredns.io) to support many more use cases than
kube-dns does by modifying the CoreDNS configuration ("Corefile").
For more information, see the [documentation](https://coredns.io/plugins/kubernetes/)
for the `kubernetes` CoreDNS plugin, or read the 
[Custom DNS Entries for Kubernetes](https://coredns.io/2017/05/08/custom-dns-entries-for-kubernetes/).
in the CoreDNS blog.