Code change:
<ins> --- reviewers: - rickypai - thockin title: Adding entries to Pod /etc/hosts with HostAliases content_type: task weight: 60 min-kubernetes-server-version: 1.7 --- <!-- 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. 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. <!-- steps --> ## Default hosts file content Start an Nginx Pod which is assigned a Pod IP: ```shell kubectl run nginx --image nginx ``` ``` pod/nginx created ``` Examine a Pod IP: ```shell kubectl get pods --output=wide ``` ``` NAME     READY     STATUS    RESTARTS   AGE    IP           NODE nginx    1/1       Running   0          13s    10.200.0.4   worker0 ``` The hosts file content would look like this: ```shell kubectl exec nginx -- cat /etc/hosts ``` ``` # Kubernetes-managed hosts file. 127.0.0.1	localhost ::1	localhost ip6-localhost ip6-loopback fe00::0	ip6-localnet fe00::0	ip6-mcastprefix fe00::1	ip6-allnodes fe00::2	ip6-allrouters 10.200.0.4	nginx ``` By default, the `hosts` file only includes IPv4 and IPv6 boilerplates like `localhost` and its own hostname. ## Adding additional entries with hostAliases 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" >}} You can start a Pod with that configuration by running: ```shell kubectl apply -f https://k8s.io/examples/service/networking/hostaliases-pod.yaml ``` ``` pod/hostaliases-pod created ``` Examine a Pod's details to see its IPv4 address and its status: ```shell kubectl get pod --output=wide ``` ``` NAME                           READY     STATUS      RESTARTS   AGE       IP              NODE hostaliases-pod                0/1       Completed   0          6s        10.200.0.5      worker0 ``` The `hosts` file content looks like this: ```shell kubectl logs hostaliases-pod ``` ``` # Kubernetes-managed hosts file. 127.0.0.1	localhost ::1	localhost ip6-localhost ip6-loopback fe00::0	ip6-localnet fe00::0	ip6-mcastprefix fe00::1	ip6-allnodes fe00::2	ip6-allrouters 10.200.0.5	hostaliases-pod # Entries added by HostAliases. 127.0.0.1	foo.local	bar.local 10.1.2.3	foo.remote	bar.remote ``` with the additional entries specified at the bottom. ## Why does the kubelet manage the hosts file? {#why-does-kubelet-manage-the-hosts-file} 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. {{< 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 >}} </ins>

Related discussion:
text: Affected page: Move this page from Concepts to Tasks (potentially under Tasks Networking). Update to redirect the old URL to the new location (use a 301 code, similar to other entries in this file). /sig docs /language en
/triage accepted /help
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I'd like to work on this one to learn something new in website page organizing. Thanks. /assign