---
layout: docs
sidebar_current: docs-builders-docker
page_title: Docker - Builders
description: |-
  The docker Packer builder builds Docker images using Docker. The builder
  starts a Docker container, runs provisioners within this container, then
  exports the container for reuse or commits the image.
---

# Docker Builder

Type: `docker`

The `docker` Packer builder builds [Docker](https://www.docker.io) images using
Docker. The builder starts a Docker container, runs provisioners within this
container, then exports the container for reuse or commits the image.

Packer builds Docker containers *without* the use of
[Dockerfiles](https://docs.docker.com/reference/builder/). By not using
Dockerfiles, Packer is able to provision containers with portable scripts or
configuration management systems that are not tied to Docker in any way. It also
has a simpler mental model: you provision containers much the same way you
provision a normal virtualized or dedicated server. For more information, read
the section on [Dockerfiles](#dockerfiles).

The Docker builder must run on a machine that has Docker installed. Therefore
the builder only works on machines that support Docker (modern Linux machines).
If you want to use Packer to build Docker containers on another platform, use
[Vagrant](https://www.vagrantup.com) to start a Linux environment, then run
Packer within that environment.

## Basic Example: Export

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

```json
{
  "type": "docker",
  "image": "ubuntu",
  "export_path": "image.tar"
}
```

## Basic Example: Commit

Below is another example, the same as above but instead of exporting the running
container, this one commits the container to an image. The image can then be
more easily tagged, pushed, etc.

```json
{
  "type": "docker",
  "image": "ubuntu",
  "commit": true
}
```

## Basic Example: Changes to Metadata

Below is an example using the changes argument of the builder. This feature allows the source images metadata to be changed when committed back into the Docker environment. It is derived from the `docker commit --change` command line [option to Docker](https://docs.docker.com/engine/reference/commandline/commit/).

Example uses of all of the options, assuming one is building an NGINX image from ubuntu as an simple example:

```json
{
  "type": "docker",
  "image": "ubuntu",
  "commit": true,
  "changes": [
    "USER www-data",
    "WORKDIR /var/www",
    "ENV HOSTNAME www.example.com",
    "VOLUME /test1 /test2",
    "EXPOSE 80 443",
    "CMD [\"nginx\", \"-g\", \"daemon off;\"]",
    "MAINTAINER Captain Kirk",
    "ENTRYPOINT /var/www/start.sh"
  ]
}
```

Allowed metadata fields that can be changed are:

- CMD
	- String, supports both array (escaped) and string form
	- EX: `"CMD [\"nginx\", \"-g\", \"daemon off;\"]"`
	- EX: `"CMD nginx -g daemon off;"`
- ENTRYPOINT
	- String
	- EX: `"ENTRYPOINT /var/www/start.sh"`
- ENV
	- String, note there is no equal sign:
	- EX: `"ENV HOSTNAME www.example.com"` not `"ENV HOSTNAME=www.example.com"`
- EXPOSE
	- String, space separated ports
	- EX: `"EXPOSE 80 443"`
- MAINTAINER
	- String
	- EX: `"MAINTAINER NAME"`
- USER
	- String
	- EX: `"USER USERNAME"`
- VOLUME
	- String
	- EX: `"VOLUME FROM TO"`
- WORKDIR
	- String
	- EX: `"WORKDIR PATH"`

## Configuration Reference

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

In addition to the options listed here, a
[communicator](/docs/templates/communicator.html) can be configured for this
builder.

### Required:

You must specify (only) one of `commit`, `discard`, or `export_path`.

- `commit` (boolean) - If true, the container will be committed to an image
    rather than exported.

- `discard` (boolean) - Throw away the container when the build is complete.
    This is useful for the [artifice
    post-processor](https://www.packer.io/docs/post-processors/artifice.html).

- `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:

- `author` (string) - Set the author (e-mail) of a commit.

- `aws_access_key` (string) - The AWS access key used to communicate with AWS.
    [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)

- `aws_secret_key` (string) - The AWS secret key used to communicate with AWS.
    [Learn how to set this.](/docs/builders/amazon.html#specifying-amazon-credentials)

- `aws_token` (string) - The AWS access token to use. This is different from the
    access key and secret key. If you're not sure what this is, then you
    probably don't need it. This will also be read from the `AWS_SESSION_TOKEN`
    environmental variable.

- `changes` (array of strings) - Dockerfile instructions to add to the commit.
    Example of instructions are `CMD`, `ENTRYPOINT`, `ENV`, and `EXPOSE`. Example:
    `[ "USER ubuntu", "WORKDIR /app", "EXPOSE 8080" ]`

- `ecr_login` (boolean) - Defaults to false. If true, the builder will login in
    order to pull the image from
    [Amazon EC2 Container Registry (ECR)](https://aws.amazon.com/ecr/).
    The builder only logs in for the duration of the pull. If true
    `login_server` is required and `login`, `login_username`, and
    `login_password` will be ignored. For more information see the
    [section on ECR](#amazon-ec2-container-registry).

- `login` (boolean) - Defaults to false. If true, the builder will login in
    order to pull the image. The builder only logs in for the duration of
    the pull. It always logs out afterwards. For log into ECR see `ecr_login`.

- `login_email` (string) - The email to use to authenticate to login.

- `login_username` (string) - The username to use to authenticate to login.

- `login_password` (string) - The password to use to authenticate to login.

- `login_server` (string) - The server address to login to.

- `message` (string) - Set a message for the commit.

- `privileged` (boolean) - If true, run the docker container with the
    `--privileged` flag. This defaults to false if not set.

- `pull` (boolean) - 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.

- `run_command` (array of strings) - An array of arguments to pass to
    `docker run` in order to run the container. By default this is set to
    `["-d", "-i", "-t", "{{.Image}}", "/bin/bash"]`. As you can see, you have a
    couple template variables to customize, as well.

- `volumes` (map of strings to strings) - A mapping of additional volumes to
    mount into this container. The key of the object is the host path, the value
    is the container path.

## Using the Artifact: Export

Once the tar artifact has been generated, you will likely want to import, tag,
and push it to a container repository. Packer can do this for you automatically
with the [docker-import](/docs/post-processors/docker-import.html) and
[docker-push](/docs/post-processors/docker-push.html) post-processors.

**Note:** This section is covering how to use an artifact that has been
*exported*. More specifically, if you set `export_path` in your configuration.
If you set `commit`, see the next section.

The example below shows a full configuration that would import and push the
created image. This is accomplished using a sequence definition (a collection of
post-processors that are treated as as single pipeline, see
[Post-Processors](/docs/templates/post-processors.html) for more information):

```json
{
  "post-processors": [
    [
      {
        "type": "docker-import",
        "repository": "mitchellh/packer",
        "tag": "0.7"
      },
      "docker-push"
    ]
  ]
}
```

In the above example, the result of each builder is passed through the defined
sequence of post-processors starting first with the `docker-import`
post-processor which will import the artifact as a docker image. The resulting
docker image is then passed on to the `docker-push` post-processor which handles
pushing the image to a container repository.

If you want to do this manually, however, perhaps from a script, you can import
the image using the process below:

```shell
$ docker import - registry.mydomain.com/mycontainer:latest < artifact.tar
```

You can then add additional tags and push the image as usual with `docker tag`
and `docker push`, respectively.

## Using the Artifact: Committed

If you committed your container to an image, you probably want to tag, save,
push, etc. Packer can do this automatically for you. An example is shown below
which tags and pushes an image. This is accomplished using a sequence definition
(a collection of post-processors that are treated as as single pipeline, see
[Post-Processors](/docs/templates/post-processors.html) for more information):

```json
{
  "post-processors": [
    [
      {
        "type": "docker-tag",
        "repository": "mitchellh/packer",
        "tag": "0.7"
      },
      "docker-push"
    ]
  ]
}
```

In the above example, the result of each builder is passed through the defined
sequence of post-processors starting first with the `docker-tag` post-processor
which tags the committed image with the supplied repository and tag information.
Once tagged, the resulting artifact is then passed on to the `docker-push`
post-processor which handles pushing the image to a container repository.

Going a step further, if you wanted to tag and push an image to multiple
container repositories, this could be accomplished by defining two,
nearly-identical sequence definitions, as demonstrated by the example below:

```json
{
  "post-processors": [
    [
      {
        "type": "docker-tag",
        "repository": "mitchellh/packer",
        "tag": "0.7"
      },
      "docker-push"
    ],
    [
      {
        "type": "docker-tag",
        "repository": "hashicorp/packer",
        "tag": "0.7"
      },
      "docker-push"
    ]
  ]
}
```

<span id="amazon-ec2-container-registry"></span>

## Amazon EC2 Container Registry

Packer can tag and push images for use in
[Amazon EC2 Container Registry](https://aws.amazon.com/ecr/). The post
processors work as described above and example configuration properties are
shown below:

```json
{
  "post-processors": [
    [
      {
        "type": "docker-tag",
        "repository": "12345.dkr.ecr.us-east-1.amazonaws.com/packer",
        "tag": "0.7"
      },
      {
        "type": "docker-push",
        "ecr_login": true,
        "aws_access_key": "YOUR KEY HERE",
        "aws_secret_key": "YOUR SECRET KEY HERE",
        "login_server": "https://12345.dkr.ecr.us-east-1.amazonaws.com/"
      }
    ]
  ]
}
```

[Learn how to set Amazon AWS credentials.](/docs/builders/amazon.html#specifying-amazon-credentials)

## Dockerfiles

This builder allows you to build Docker images *without* Dockerfiles.

With this builder, you can repeatably create Docker images without the use of 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
virtualized or dedicated machine.

While Docker has many features, Packer views Docker simply as an container
runner. To that end, Packer is able to repeatably build these containers
using portable provisioning scripts.

Dockerfiles have some additional features that Packer doesn't support which are
able to be worked around. Many of these features will be automated by Packer in
the future:

- Dockerfiles will snapshot the container at each step, allowing you to go
    back to any step in the history of building. Packer doesn't do this yet, but
    inter-step snapshotting is on the way.

- Dockerfiles can contain information such as exposed ports, shared volumes,
    and other metadata. Packer builds a raw Docker container image that has none
    of this metadata. You can pass in much of this metadata at runtime with
    `docker run`.

## Overriding the host directory

By default, Packer creates a temporary folder under your home directory, and
uses that to stage files for uploading into the container. If you would like to
change the path to this temporary folder, you can set the `PACKER_TMP_DIR`
environment variable. This can be useful, for example, if you have your home
directory permissions set up to disallow access from the docker daemon.
