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Tidy task page about using HostAliases

pull/21439/head
Tim Bannister 2020-06-02 23:44:17 +01:00
parent b635757bc0
commit 5d358120fb
1 changed files with 29 additions and 27 deletions
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content/en/docs/concepts/services-networking/add-entries-to-pod-etc-hosts-with-host-aliases.md
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@ -5,27 +5,29 @@ reviewers:
title: Adding entries to Pod /etc/hosts with HostAliases
content_type: concept
weight: 60
min-kubernetes-server-version: 1.7
---
{{< toc >}}
<!-- overview -->
Adding entries to a Pod's /etc/hosts file provides Pod-level override of hostname resolution when DNS and other options are not applicable. In 1.7, users can add these custom entries with the HostAliases field in PodSpec.
Modification not using HostAliases is not suggested because the file is managed by Kubelet and can be overwritten on during Pod creation/restart.
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.
Modification not using HostAliases is not suggested because the file is managed by the kubelet and can be overwritten on during Pod creation/restart.
<!-- body -->
## Default Hosts File Content
## Default hosts file content
Let's start an Nginx Pod which is assigned a Pod IP:
Start an Nginx Pod which is assigned a Pod IP:
```shell
kubectl run nginx --image nginx --generator=run-pod/v1
```
```shell
```
pod/nginx created
```
@ -35,7 +37,7 @@ Examine a Pod IP:
kubectl get pods --output=wide
```
```shell
```
NAME READY STATUS RESTARTS AGE IP NODE
nginx 1/1 Running 0 13s 10.200.0.4 worker0
```
@ -46,7 +48,7 @@ The hosts file content would look like this:
kubectl exec nginx -- cat /etc/hosts
```
```none
```
# Kubernetes-managed hosts file.
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
@ -60,43 +62,44 @@ fe00::2 ip6-allrouters
By default, the `hosts` file only includes IPv4 and IPv6 boilerplates like
`localhost` and its own hostname.
## Adding Additional Entries with HostAliases
## Adding additional entries with hostAliases
In addition to the default boilerplate, we can add additional entries to the
`hosts` file to resolve `foo.local`, `bar.local` to `127.0.0.1` and `foo.remote`,
`bar.remote` to `10.1.2.3`, we can by adding HostAliases to the Pod under
In addition to the default boilerplate, you can add additional entries to the
`hosts` file.
For example: to resolve `foo.local`, `bar.local` to `127.0.0.1` and `foo.remote`,
`bar.remote` to `10.1.2.3`, you can configure HostAliases for a Pod under
`.spec.hostAliases`:
{{< codenew file="service/networking/hostaliases-pod.yaml" >}}
This Pod can be started with the following commands:
Yoyu can start a Pod with that configuration by running:
```shell
kubectl apply -f hostaliases-pod.yaml
kubectl apply -f https://k8s.io/examples/service/networking/hostaliases-pod.yaml
```
```shell
```
pod/hostaliases-pod created
```
Examine a Pod IP and status:
Examine a Pod's details to see its IPv4 address and its status:
```shell
kubectl get pod --output=wide
```
```shell
```
NAME READY STATUS RESTARTS AGE IP NODE
hostaliases-pod 0/1 Completed 0 6s 10.200.0.5 worker0
```
The `hosts` file content would look like this:
The `hosts` file content looks like this:
```shell
kubectl logs hostaliases-pod
```
```none
```
# Kubernetes-managed hosts file.
127.0.0.1 localhost
::1 localhost ip6-localhost ip6-loopback
@ -111,19 +114,18 @@ fe00::2 ip6-allrouters
10.1.2.3 foo.remote bar.remote
```
With the additional entries specified at the bottom.
with the additional entries specified at the bottom.
## Why Does Kubelet Manage the Hosts File?
## Why does the kubelet manage the hosts file? {#why-does-kubelet-manage-the-hosts-file}
Kubelet [manages](https://github.com/kubernetes/kubernetes/issues/14633) the
The kubelet [manages](https://github.com/kubernetes/kubernetes/issues/14633) the
`hosts` file for each container of the Pod to prevent Docker from
[modifying](https://github.com/moby/moby/issues/17190) the file after the
containers have already been started.
Because of the managed-nature of the file, any user-written content will be
overwritten whenever the `hosts` file is remounted by Kubelet in the event of
a container restart or a Pod reschedule. Thus, it is not suggested to modify
the contents of the file.
{{< caution >}}
Avoid making manual changes to the hosts file inside a container.
If you make manual changes to the hosts file,
those changes are lost when the container exits.
{{< /caution >}}