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:
CoreDNS is a flexible, extensible DNS server that can serve as the Kubernetes cluster DNS. Like Kubernetes, the CoreDNS project is hosted by the 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.
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.
kubeadm v1.27, the only supported cluster DNS application
You can move to CoreDNS when you use
kubeadm to upgrade a cluster that is
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.
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
can take care of retaining the existing CoreDNS configuration automatically.
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.
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
kubernetes CoreDNS plugin, or read the
Custom DNS Entries for Kubernetes.
in the CoreDNS blog.