# `Nerves.Artifact.BuildRunners.Docker`
[🔗](https://github.com/nerves-project/nerves/blob/v1.14.1/lib/nerves/artifact/build_runners/docker.ex#L11)

Produce an artifact for a package using Docker.

The Nerves Docker artifact build_runner will use docker to create the artifact
for the package. The output in Mix will be limited to the headlines from the
process and the full build log can be found in the file `build.log` located
root of the package path.

## Images

Docker containers will be created based off the image that is loaded.
By default, containers will use the default image
`ghcr.io/nerves-project/nerves_system_br:latest`. Sometimes additional host tools
are required to build a package. Therefore, packages can provide their own
images by specifying it in the package config under `:build_runner_config`.
the file is specified as a tuple `{"path/to/Dockerfile", tag_name}`.

Example:

    build_runner_config: [
      docker: {"Dockerfile", "my_system:0.1.0"}
    ]

## Volumes and Cache

Nerves will mount several volumes to the container for use in building
the artifact.

Mounted from the host:

  * `/nerves/env/<package.name>` - The package being built.
  * `/nerves/env/platform` - The package platform package.
  * `/nerves/host/artifacts` - The host artifact directory.

Nerves will also mount the host NERVES_DL_DIR to save downloaded assets the
build platform requires for producing the artifact.
This is mounted at `/nerves/dl`. This volume can significantly reduce build
times but has potential for corruption. If you suspect that your build is
failing due to a faulty downloaded cached data, you can manually mount
the offending container and remove the file from this location or delete the
entire directory.

Nerves uses a docker volume to attach the build files. The volume name is
defined as the package name and a unique id that is stored at
`ARTIFACT_DIR/.docker_id`. The build directory is mounted to the container at
`/nerves/build` and is configured as the current working directory.

## Cleanup

Periodically, you may want to destroy all unused volumes to clean up.
Please refer to the Docker documentation for more information on how to
do this.

When the build_runner is finished, the artifact is decompressed on the host at
the packages defined artifact directory.

# `build`

Create an artifact for the package

Opts:
  `make_args:` - Extra arguments to be passed to make.

  For example:

  You can configure the number of parallel jobs that buildroot
  can use for execution. This is useful for situations where you may
  have a machine with a lot of CPUs but not enough ram.

    # mix.exs
    defp nerves_package do
      [
        # ...
        build_runner_opts: [make_args: ["PARALLEL_JOBS=8"]],
      ]
    end

# `parse_docker_version`

```elixir
@spec parse_docker_version(String.t()) :: {:ok, Version.t()} | :error
```

# `system_shell`

```elixir
@spec system_shell(Nerves.Package.t()) :: :ok
```

Connect to a system configuration shell in a Docker container

---

*Consult [api-reference.md](api-reference.md) for complete listing*