Maciej Szulik
00f502fa6a
kubectl run starting from 1.18 is creating only Pods and there is no option to create any other resource. Users should be using kubectl create commands instead. This update the documentation in all those places where kubectl create should be used instead or changes description to reflect the situation.
131 lines
3.1 KiB
Markdown
131 lines
3.1 KiB
Markdown
---
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reviewers:
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- rickypai
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- thockin
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title: Adding entries to Pod /etc/hosts with HostAliases
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content_type: concept
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weight: 60
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min-kubernetes-server-version: 1.7
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---
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<!-- overview -->
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Adding entries to a Pod's `/etc/hosts` file provides Pod-level override of hostname resolution when DNS and other options are not applicable. You can add these custom entries with the HostAliases field in PodSpec.
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Modification not using HostAliases is not suggested because the file is managed by the kubelet and can be overwritten on during Pod creation/restart.
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<!-- body -->
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## Default hosts file content
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Start an Nginx Pod which is assigned a Pod IP:
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```shell
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kubectl run nginx --image nginx
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```
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```
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pod/nginx created
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```
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Examine a Pod IP:
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```shell
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kubectl get pods --output=wide
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```
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```
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NAME READY STATUS RESTARTS AGE IP NODE
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nginx 1/1 Running 0 13s 10.200.0.4 worker0
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```
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The hosts file content would look like this:
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```shell
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kubectl exec nginx -- cat /etc/hosts
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```
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```
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# Kubernetes-managed hosts file.
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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fe00::0 ip6-mcastprefix
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fe00::1 ip6-allnodes
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fe00::2 ip6-allrouters
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10.200.0.4 nginx
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```
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By default, the `hosts` file only includes IPv4 and IPv6 boilerplates like
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`localhost` and its own hostname.
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## Adding additional entries with hostAliases
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In addition to the default boilerplate, you can add additional entries to the
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`hosts` file.
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For example: to resolve `foo.local`, `bar.local` to `127.0.0.1` and `foo.remote`,
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`bar.remote` to `10.1.2.3`, you can configure HostAliases for a Pod under
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`.spec.hostAliases`:
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{{< codenew file="service/networking/hostaliases-pod.yaml" >}}
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You can start a Pod with that configuration by running:
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```shell
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kubectl apply -f https://k8s.io/examples/service/networking/hostaliases-pod.yaml
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```
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```
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pod/hostaliases-pod created
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```
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Examine a Pod's details to see its IPv4 address and its status:
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```shell
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kubectl get pod --output=wide
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```
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```
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NAME READY STATUS RESTARTS AGE IP NODE
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hostaliases-pod 0/1 Completed 0 6s 10.200.0.5 worker0
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```
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The `hosts` file content looks like this:
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```shell
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kubectl logs hostaliases-pod
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```
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```
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# Kubernetes-managed hosts file.
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127.0.0.1 localhost
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::1 localhost ip6-localhost ip6-loopback
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fe00::0 ip6-localnet
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fe00::0 ip6-mcastprefix
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fe00::1 ip6-allnodes
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fe00::2 ip6-allrouters
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10.200.0.5 hostaliases-pod
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# Entries added by HostAliases.
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127.0.0.1 foo.local bar.local
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10.1.2.3 foo.remote bar.remote
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```
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with the additional entries specified at the bottom.
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## Why does the kubelet manage the hosts file? {#why-does-kubelet-manage-the-hosts-file}
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The kubelet [manages](https://github.com/kubernetes/kubernetes/issues/14633) the
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`hosts` file for each container of the Pod to prevent Docker from
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[modifying](https://github.com/moby/moby/issues/17190) the file after the
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containers have already been started.
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{{< caution >}}
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Avoid making manual changes to the hosts file inside a container.
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If you make manual changes to the hosts file,
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those changes are lost when the container exits.
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{{< /caution >}}
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