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| reviewers | title | min-kubernetes-server-version | content_type | |
|---|---|---|---|---|
|
Using CoreDNS for Service Discovery | v1.9 | task |
This page describes the CoreDNS upgrade process and how to install CoreDNS instead of kube-dns.
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About CoreDNS
CoreDNS is a flexible, extensible DNS server that can serve as the Kubernetes cluster DNS. Like Kubernetes, the CoreDNS project is hosted by the {{< glossary_tooltip text="CNCF" term_id="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 GitHub project.
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{{< skew currentVersion >}}, 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.
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. 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.
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You can configure CoreDNS to support many more use cases than
kube-dns does by modifying the CoreDNS configuration ("Corefile").
For more information, see the documentation
for the kubernetes CoreDNS plugin, or read the
Custom DNS Entries for Kubernetes.
in the CoreDNS blog.