76 lines
2.9 KiB
Markdown
76 lines
2.9 KiB
Markdown
---
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assignees:
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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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redirect_from:
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- "/docs/user-guide/add-entries-to-pod-etc-hosts-with-host-aliases/"
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- "/docs/user-guide/add-entries-to-pod-etc-hosts-with-host-aliases.md"
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---
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* TOC
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{:toc}
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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. In 1.7, users 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 Kubelet and can be overwritten on during Pod creation/restart.
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## Default Hosts File Content
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Lets start an Nginx Pod which is assigned an Pod IP:
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```
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$ kubectl get pods --output=wide
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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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```
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$ kubectl exec nginx -- cat /etc/hosts
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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 `localhost` and its own hostname.
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## Adding Additional Entries with HostAliases
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In addition the 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 `.spec.hostAliases`:
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{% include code.html language="yaml" file="hostaliases-pod.yaml" ghlink="/docs/concepts/services-networking/hostaliases-pod.yaml" %}
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The hosts file content would look like this:
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```
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$ kubectl logs hostaliases-pod
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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 hostaliases-pod
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127.0.0.1 foo.local
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127.0.0.1 bar.local
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10.1.2.3 foo.remote
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10.1.2.3 bar.remote
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```
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With the additional entries specified at the bottom.
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## Limitations
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As of 1.7, Pods with hostNetwork enabled will not be able to use this feature. This is because kubelet only manages the hosts file for non-hostNetwork Pods. There are ongoing discussions to change this.
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## Why Does Kubelet Manage the Hosts File?
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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.
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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.
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