---
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.
page_title: Docker - Builders
sidebar_title: Docker
---

# Docker Builder

Type: `docker`
Artifact BuilderId: `packer.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/engine/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 simple 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 Engine installed.
Therefore the builder only works on machines that support Docker and _does not
support running on a Docker remote host_. You can learn about what [platforms
Docker supports and how to install onto
them](https://docs.docker.com/engine/installation/) in the Docker
documentation.

## 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.

<Tabs>
<Tab heading="JSON">

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

</Tab>
<Tab heading="HCL2">

```hcl
source "docker" "example" {
    image = "ubuntu"
    export_path = "image.tar"
}

build {
  sources = ["source.docker.example"]
}
```

</Tab>
</Tabs>

## 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.

<Tabs>
<Tab heading="JSON">

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

</Tab>
<Tab heading="HCL2">

```hcl
source "docker" "example" {
    image = "ubuntu"
    commit = true
}

build {
  sources = ["source.docker.example"]
}
```

</Tab>
</Tabs>

## 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:

<Tabs>
<Tab heading="JSON">

```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",
    "LABEL version=1.0",
    "ONBUILD RUN date",
    "CMD [\"nginx\", \"-g\", \"daemon off;\"]",
    "ENTRYPOINT /var/www/start.sh"
  ]
}
```

</Tab>
<Tab heading="HCL2">

```hcl
source "docker" "example" {
    image = "ubuntu"
    commit = true
      changes = [
      "USER www-data",
      "WORKDIR /var/www",
      "ENV HOSTNAME www.example.com",
      "VOLUME /test1 /test2",
      "EXPOSE 80 443",
      "LABEL version=1.0",
      "ONBUILD RUN date",
      "CMD [\"nginx\", \"-g\", \"daemon off;\"]",
      "ENTRYPOINT /var/www/start.sh"
    ]
}
```

</Tab>
</Tabs>

Allowed metadata fields that can be changed are:

- CMD
  - String, supports both array (escaped) and string form
  - EX: `"CMD [\"nginx\", \"-g\", \"daemon off;\"]"` corresponds to Docker exec form
  - EX: `"CMD nginx -g daemon off;"` corresponds to Docker shell form, invokes a command shell first
- ENTRYPOINT
  - String, supports both array (escaped) and string form
  - EX: `"ENTRYPOINT [\"/bin/sh\", \"-c\", \"/var/www/start.sh\"]"` corresponds to Docker exec form
  - EX: `"ENTRYPOINT /var/www/start.sh"` corresponds to Docker shell form, invokes a command shell first
- 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"`
- LABEL
  - String, space separated key=value pairs
  - EX: `"LABEL version=1.0"`
- ONBUILD
  - String
  - EX: `"ONBUILD RUN date"`
- MAINTAINER
  - String, deprecated in Docker version 1.13.0
  - 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.

The Docker builder uses a special Docker communicator _and will not use_ the
standard [communicators](/docs/templates/legacy_json_templates/communicator).

### Required:

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

@include 'builder/docker/Config-required.mdx'

### Optional:

@include 'builder/docker/AwsAccessConfig-not-required.mdx'

@include 'builder/docker/Config-not-required.mdx'

## Build Shared Information Variables

This build shares generated data with provisioners and post-processors via [template engines](/docs/templates/legacy_json_templates/engine)
for JSON and [contextual variables](/docs/templates/hcl_templates/contextual-variables) for HCL2.

The generated variable available for this builder is:

- `ImageSha256` - When committing a container to an image, this will give the image SHA256. Because the image is not available at the provision step,
  this variable is only available for post-processors.

## 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) and
[docker-push](/docs/post-processors/docker-push) 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/legacy_json_templates/post-processors) for more information):

<Tabs>
<Tab heading="JSON">

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

</Tab>
<Tab heading="HCL2">

```hcl
  post-processors {
    post-processor "docker-import" {
        repository =  "myrepo/myimage"
        tag = ["0.7"]
      }
    post-processor "docker-push" {}
  }
}
```

</Tab>
</Tabs>

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-session
$ 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/legacy_json_templates/post-processors) for more
information):

<Tabs>
<Tab heading="JSON">

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

</Tab>
<Tab heading="HCL2">

```hcl
  post-processors {
    post-processor "docker-tag" {
        repository =  "myrepo/myimage"
        tag = ["0.7"]
      }
    post-processor "docker-push" {}
  }
}
```

</Tab>
</Tabs>

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:

<Tabs>
<Tab heading="JSON">

```json
{
  "post-processors": [
    [
      {
        "type": "docker-tag",
        "repository": "myrepo/myimage1",
        "tag": "0.7"
      },
      "docker-push"
    ],
    [
      {
        "type": "docker-tag",
        "repository": "myrepo/myimage2",
        "tag": "0.7"
      },
      "docker-push"
    ]
  ]
}
```

</Tab>
<Tab heading="HCL2">

```hcl
  post-processors {
    post-processor "docker-tag" {
        repository =  "myrepo/myimage1"
        tag = ["0.7"]
      }
    post-processor "docker-push" {}
  }
  post-processors {
    post-processor "docker-tag" {
        repository =  "myrepo/myimage2"
        tag = ["0.7"]
      }
    post-processor "docker-push" {}
  }
}
```

</Tab>
</Tabs>

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

## Docker For Windows

You should be able to run docker builds against both linux and Windows
containers. Windows containers use a different communicator than linux
containers, because Windows containers cannot use `docker cp`.

If you are building a Windows container, you must set the template option
`"windows_container": true`. Please note that docker cannot export Windows
containers, so you must either commit or discard them.

The following is a fully functional template for building a Windows
container.

<Tabs>
<Tab heading="JSON">

```json
{
  "builders": [
    {
      "type": "docker",
      "image": "microsoft/windowsservercore:1709",
      "container_dir": "c:/app",
      "windows_container": true,
      "commit": true
    }
  ]
}
```

</Tab>
<Tab heading="HCL2">

```hcl
source "docker" "windows" {
    image = "ubuntu"
    container_dir = "c:/app"
    windows_container = true
    commit = true
}

build {
  sources = ["source.docker.example"]
}
```

</Tab>
</Tabs>

## 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:

<Tabs>
<Tab heading="JSON">

```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/"
      }
    ]
  ]
}
```

</Tab>
<Tab heading="HCL2">

```hcl
post-processors {
  post-processor "docker-tag" {
      repository = "12345.dkr.ecr.us-east-1.amazonaws.com/packer"
      tag = ["0.7"]
  }
  post-processor "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/"
  }
}
```

</Tab>
</Tabs>

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

## Dockerfiles

This builder allows you to build Docker images _without_ Dockerfiles.

With this builder, you can repeatedly 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 a container
runner. To that end, Packer is able to repeatedly build these containers using
portable provisioning scripts.

## 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`.
This can be useful, for example, if you have your home directory permissions
set up to disallow access from the docker daemon.
