packer-cn/website/source/docs/builders/docker.html.markdown

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layout: "docs"
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# Docker Builder

Type: `docker`

The Docker builder builds [Docker](http://www.docker.io) images using
Docker. The builder starts a Docker container, runs provisioners within
this container, then exports the container for re-use.

The Docker builder must run on a machine that supports Docker.

## Basic Example

Below is a fully functioning example. It doesn't do anything useful, since
no provisioners are defined, but it will effectively repackage an image.

<pre class="prettyprint">
{
  "type": "docker",
  "image": "ubuntu",
  "export_path": "image.tar"
}
</pre>

## Configuration Reference

Configuration options are organized below into two categories: required and optional. Within
each category, the available options are alphabetized and described.

Required:

* `export_path` (string) - The path where the final container will be exported
  as a tar file.

* `image` (string) - The base image for the Docker container that will
  be started. This image will be pulled from the Docker registry if it
  doesn't already exist.

Optional:

* `pull` (bool) - If true, the configured image will be pulled using
  `docker pull` prior to use. Otherwise, it is assumed the image already
  exists and can be used. This defaults to true if not set.

## Dockerfiles

This builder allows you to build Docker images _without_ Dockerfiles. If
you have a Dockerfile already made, it is simple to just run `docker build`
manually.

With this builder, you can repeatably create Docker images without the use
a Dockerfile. You don't need to know the syntax or semantics of Dockerfiles.
Instead, you can just provide shell scripts, Chef recipes, Puppet manifests,
etc. to provision your Docker container just like you would a regular machine.