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Improve coredns page 

This PR refactors the coredns page by removing some outdated statements.
pull/32126/head
Qiming Teng 2022-03-08 21:09:37 +08:00
parent 3668b41e34
commit 15f643e5e8
1 changed files with 33 additions and 37 deletions
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70
content/en/docs/tasks/administer-cluster/coredns.md
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@ -19,11 +19,14 @@ This page describes the CoreDNS upgrade process and how to install CoreDNS inste
## 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 {{< glossary_tooltip text="CNCF" term_id="cncf" >}}.
[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
{{< 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.
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
@ -34,51 +37,44 @@ For manual deployment or replacement of kube-dns, see the documentation at the
### 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
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.
If you are moving from kube-dns to CoreDNS, make sure to set the `CoreDNS` feature gate to `true`
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.
## Upgrading CoreDNS
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](https://github.com/coredns/deployment/blob/master/kubernetes/CoreDNS-k8s_version.md).
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.
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.
## Tuning CoreDNS
When resource utilisation is a concern, it may be useful to tune the configuration of CoreDNS. For more details, check out the
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).
## {{% heading "whatsnext" %}}
You can configure [CoreDNS](https://coredns.io) to support many more use cases than
kube-dns by modifying the `Corefile`. For more information, see the
[CoreDNS site](https://coredns.io/2017/05/08/custom-dns-entries-for-kubernetes/).
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.