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coredns: update notes in administer-cluster/coredns.md (#8697)

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CoreDNS is installed by default in 1.11.
Add notes on how to install kube-dns instead.

Update notes about CoreDNS->CoreDNS upgrades as in 1.11
the Corefile is retained.

Add example on upgrading from kube-dns to CoreDNS.
This commit is contained in:
Lubomir I. Ivanov
2018-05-25 16:39:33 +03:00
committed by Misty Linville
parent 18f8bf969c
commit d87adaba27
1 changed files with 18 additions and 28 deletions
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content/en/docs/tasks/administer-cluster/coredns.md
+18 -28
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@@ -6,11 +6,8 @@ min-kubernetes-server-version: v1.9
content_template: templates/task
---
{{< feature-state state="beta" >}}
{{% capture overview %}}
This page describes how to enable CoreDNS instead of kube-dns for service
discovery.
This page describes the CoreDNS upgrade process and how to install kube-dns instead of CoreDNS.
{{% /capture %}}
{{% capture prerequisites %}}
@@ -19,41 +16,34 @@ discovery.
{{% capture steps %}}
## Installing CoreDNS with kubeadm
In Kubernetes 1.9, [CoreDNS](https://coredns.io) is available as an alpha feature, and
in Kubernetes 1.10 it is available as a beta feature. In either case, you may install
it during cluster creation by setting the `CoreDNS` feature gate to `true` during `kubeadm init`:
## Installing kube-dns with kubeadm
In Kubernetes 1.11, [CoreDNS](https://coredns.io) has graduated to General Availability (GA)
and is installed by default. To install kube-dns instead, set the `CoreDNS` feature gate
value to `false`:
```
kubeadm init --feature-gates=CoreDNS=true
```
This installs CoreDNS instead of kube-dns.
## Using a custom CoreDNS image repository with kubeadm
To use a custom image repository for the CoreDNS image, e.g. one located in your own Docker registry,
you can execute the following command after kubeadm has deployed the CoreDNS manifest:
```shell
kubectl set image -n kube-system deploy/coredns coredns=prefix.example.com/coredns/coredns:1.0.6
kubeadm init --feature-gates=CoreDNS=false
```
## Upgrading an Existing Cluster with kubeadm
In Kubernetes 1.10, you can also move to CoreDNS when you use `kubeadm` to upgrade
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
("Corefile") based upon the `kube-dns` ConfigMap, preserving configurations for federation,
stub domains, and upstream name server.
Note that if you are running CoreDNS in your cluster already, prior to upgrade, your existing 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 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
```
This process will be modified for the GA release of this feature, such that an existing
Corefile will not be overwritten.
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.
{{% /capture %}}