Using CoreDNS for Service Discovery [page]deterministic

tasksnetworking

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

## 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 [CNCF](#gloss:cncf).

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` v, 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).

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.

Sources

tasks/administer-cluster/coredns.md · doc — “Using CoreDNS for Service Discovery”

Related (10)

references Cloud Native Computing Foundation (CNCF) — CNCF conf=1

part_of {{% heading "prerequisites" %}} — describes conf=1

part_of About CoreDNS — describes conf=1

part_of Installing CoreDNS — describes conf=1

part_of Migrating to CoreDNS — describes conf=1

part_of Upgrading CoreDNS — describes conf=1

part_of Tuning CoreDNS — describes conf=1

part_of {{% heading "whatsnext" %}} — describes conf=1

part_of Upgrading an existing cluster with kubeadm — describes conf=1

api_for Service — documents API object conf=1

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