buildrunner 3.22.1
Docker-based build tool
License: MIT
Requires Python: >=3.9

#############
 Buildrunner
#############

Build and publish Docker images, run builds/tasks within Docker containers or
on remote hosts.

.. contents::
   :local:

Overview
========

Buildrunner is a tool written on top of Docker and ssh remoting frameworks that
allows engineers to do the following:

- Build and publish Docker images
- Run other build and packaging tools within custom Docker containers while
  collecting the artifacts these tools produce
- Run builds/tasks on remote systems that cannot be done within a Docker
  container
- Creating ad-hoc environments using Docker containers for running automated,
  self-contained integration and functional tests

Buildrunner runs builds and tests by reading configuration files within a given
source tree. This allows build and continuous integration test configurations
to live close to source files, providing engineers the ability to update and
version the build and test configuration right along with the code that is
being built and tested. This also allows build tools and infrastructures to
very easily import and setup builds for new modules and branches.

Installation
============

See `docs/installation <docs/installation.rst>`_.

Development
============

See `docs/development <docs/development.rst>`__.

Global Configuration
====================

See `docs/global-configuration <docs/global-configuration.rst>`_.

Buildrunner Builds
==================

A Buildrunner build consists of one or more build steps.

Each step may build a custom Docker image and run a task within a specific
Docker container or run commands on a remote host.

Artifacts can be collected from tasks run within containers or remote hosts
when they have finished running and archived in your build system (Jenkins, for
instance).

Resulting images (either from a build phase or a run phase) can be committed or
pushed to the central or a private Docker image registry for use in other
builds or to run services in other environments.

Build definitions are found in the root of your source tree, either in a file
named 'buildrunner.yaml'. The build definition is simply a
yaml map defining 'steps'. Each step is given a custom name and must contain
either 'build' and/or 'run' attributes (optionally containing a 'push'
attribute) or a 'remote' attribute:

.. code:: yaml

  steps:
    step1-name:
      build: <build config>
      run: <run config>
      commit: <commit config>
      push: <push config>
      # or
      remote: <remote config>
    step2-name:
      build: <build config>
      run: <run config>
      push: <push config>
      # or
      remote: <remote config>

Step names are arbitrary--you can use whatever names you want as long as they
are unique within a given ``steps`` configuration. Archived artifacts are stored
in a step-specific results directory. To use artifacts generated from a
previous step in a subsequent one you would reference them using the previous
step name.

.. note:: Artifacts from previous steps are not available within remote builds

There are two image builders in ``buildrunner``. The default builder is
equivalent to ``docker build`` and only supports single-platform images,
this is referenced as the legacy image builder.
The new image builder is equivalent to ``docker buildx`` and is used for for both
single and multi-platform images. To use the ``docker buildx`` builder,
set ``use-legacy-builder: false`` in the configuration file or use ``platforms``
in the ``build`` section. The legacy builder will be removed in a future release.

.. code:: yaml

  use-legacy-builder: false
  steps:
    step1:
      build: <build config>
      run: <run config>
      push: <push config>
      # or
      remote: <remote config>

Jinja 
================

The 'buildrunner.yaml' file is processed as a 
`Jinja template <http://jinja.pocoo.org/>`_, meaning the build definition can be 
modified dynamically before it is run. In addition to the environment variables 
listed below in `Running Containers`_ and the standard Jinja methods, the list 
below contains available variables and methods.

:``CONFIG_FILE``: the full path to the current file being processed (buildrunner.yaml) 
:``CONFIG_DIR``: the full path to the directory containing the current file being processed
:``env``: exposes the ``os.environ`` instance to retrieve arbitrary env variables
:``read_yaml_file``: a method to read an arbitrary file in the current workspace as yaml and use the
                     contents in the script, note that the file is processed using Jinja as well and
                     that the file must exist before buildrunner is run or else this method will
                     fail
:``raise``: a method to raise an exception with the message provided as a single argument

Jinja filters
-------------

:``hash_sha1``: SHA1 hash filter
:``base64encode``:  Base64 encoding filter
:``base64decode``: Base64 decoding filter
:``re_sub``: performs a regular expression replacement on text
:``re_split``: uses a pattern to split text

Steps Dependencies
==========================
Buildrunner supports specifying steps dependencies. To use this 
feature a user must specify the configuration version of ``2.0`` or higher and
also use the configuration keyword ``depends`` in the step configuration. The ``depends``
key takes a list of step names which must be completed before the execution of the 
current step.

.. code:: yaml
  
  version: 2.0
  steps:
    step1:
      run:
        image: {{ DOCKER_REGISTRY }}/ubuntu:latest
        cmd: echo "Hello from step1"
    step2:
      depends:
        - step1
        - step3
      run:
        image: {{ DOCKER_REGISTRY }}/ubuntu:latest
        cmd: echo "Hello from step 2"
    step3: 
      run:
        image: {{ DOCKER_REGISTRY }}/ubuntu:latest
        cmd: echo "Hello from step 3."  
    step4: 
      run: 
        image: {{ DOCKER_REGISTRY }}/ubuntu:latest 
        cmd: echo "Hello from step 4." 

The step execution order will be in the order it appears in the configuration
unless an dependency is defined by using ``depends``, then the order will 
change in order to satisfy the dependencies. The ``graphlib`` library is used 
to generate the directed acyclic graph and there is no guarantee how non-dependent
steps will be ordered.
An example of a step order which satisfies the dependencies in the config above:
``('step1', 'step3', 'step4', 'step2')``. Please note that there are other valid 
permutations as well.

Circular dependencies are not valid. If a circular dependency is in a configuration 
it will produce an exeception and halt the execution of buildrunner.

Standard Docker Builds (the ``build`` step attribute)
=====================================================

Buildrunner allows you to build a Docker image using a standard Dockerfile.
This is done using the top-level 'build' attribute in a step configuration. The
value of the 'build' attribute can either be a single string value indicating
the directory to use for the Docker build context (the directory containing the
Dockerfile) or a map that describes a dynamic build context and/or other build
arguments.

Here is an example of a build definition that would build a Docker image using
the root directory of the source tree as the build context (equivalent to
running 'docker build .' in the root of your source tree):

.. code:: yaml

  steps:
    build-my-container:
      build: .

If the Dockerfile is in another directory within the source tree just give the
relative path as the argument to the build attribute:

.. code:: yaml

  steps:
    build-my-container:
      build: my/container/build/context

By placing different contexts in different directories a single source tree can
produce multiple Docker images:

.. code:: yaml

  steps:
    build-container-1:
      build: container-1
    build-container-2:
      build: container-2

The value of the 'build' attribute can also be a map. The following example
shows the different configuration options available:

.. code:: yaml

  steps:
    build-my-container:
      build:
        # Define the base context directory (same as string-only value)
        path: my/container/build/context

        # The inject map specifies other files outside the build context that
        # should be included in the context sent to the Docker daemon. Files
        # injected into the build context override files with the same name/path
        # contained in the path configuration above.
        #
        # NOTE: you do not need to specify a path attribute if you inject all
        # of the files you need, including a Dockerfile. When the path attribute
        # is NOT explicitly specified (either as 'path: .' or 'build: .'), the
        # source directory will NOT be copied into the build context. This
        # optimization improves build performance by avoiding unnecessary file
        # copying. Any files needed by the Dockerfile must be explicitly injected
        # when not specifying a path.
        #
        # NOTE: if the destination is a directory then it must be indicated with
        # an ending "/" or a "." component.
        inject:
          # Each entry in the map has a glob pattern key that resolves relative
          # to the source tree root with the value being the directory within
          # the build context that the file(s) should be copied to. These files
          # will be available to the Dockerfile at the given location during
          # the Docker build.  Destination directories must have a trailing
          # slash (``/``).
          glob/to/files.*: dest/dir/
          path/to/file1.txt: dest/dir/
          path/to/file2.txt: .
          path/to/file3.txt: dest/filename.txt

        # The path to a Dockerfile to use, or an inline Dockerfile declaration.
        # This Dockerfile overrides any provided in the path or inject
        # configurations. If the docker context does not require any additional
        # resources the path and inject configurations are not required.
        dockerfile: path/to/Dockerfile
        <or>
        dockerfile: |
          FROM someimage:latest
          RUN /some/command


        # The stage to stop at when using multi-stage docker builds
        # similar to the --target option used by docker
        target: dev

        # Whether to use the default Docker image cache for intermediate
        # images--caching images significantly speeds up the building of
        # images but may not be desired when building images for publishing
        no-cache: true/false (defaults to false)

        # The following applies to single platform builds.
        # Specify Docker images to consider as cache sources,
        # similar to the --cache-from option used by Docker.
        # Buildrunner will attempt to pull these images from the remote registry.
        # If the pull is unsuccessful, buildrunner will still pass in the image name
        # into --cache-from, allowing a cache check in the host machine cache
        cache_from:
          - my-images/image:PR-123
          - my-images/image:latest

        # The following applies to multiplatform builds.
        # Specify Docker images to consider as cache sources,
        # similar to the --cache-from option used by Docker.
        # cache_from: Works only with the container driver. Loads the cache
        #     (if needed) from a registry `cache_from="user/app:cache"`  or
        #     a directory on the client `cache_from="type=local,src=path/to/dir"`.
        #     It's also possible to use a dict or list of dict form for this
        #     argument. e.g.
        #     `cache_from={type="local", src="path/to/dir"}`
        # cache_to: Works only with the container driver. Sends the resulting
        #     docker cache either to a registry `cache_to="user/app:cache"`,
        #     or to a local directory `cache_to="type=local,dest=path/to/dir"`.
        #     It's also possible to use a dict form for this argument. e.g.
        #     `cache_to={type="local", dest="path/to/dir", mode="max"}`
        cache_from: my-images/image:PR-123
        <or>
        cache_from:
          - type: local
            src: path/to/dir

        cache_to:
          type: local
          dest: path/to/dir
          mode: max


        # Whether to do a docker pull of the "FROM" image prior to the build.
        # This is critical if you are building from images that are changing
        # with regularity.
        # NOTE: If the image was created from a 'push' or 'commit' earlier in
        #       this ``buildrunner.yaml`` then this will default to false
        # NOTE: The command line argument ``--local-images`` can be used to temporarily
        #       override and assume ``pull: false`` for the build without rewriting
        #       ``buildrunner.yaml``.
        pull: true/false # (default changes depending on if the
                         # image was created via buildrunner or not)

        # Specify a different platform architecture when pulling and building images
        # This is useful if you are building an image for a different architecture than what
        # buildrunner is running on, such as using a linux/amd64 build node to produce an image
        # with a docker manifest compatible with an Apple M1 linux/arm64/v8 architecture
        platform: linux/amd64
        <or>
        platform: linux/arm64/v8 # an apple m1 architecture

        # To build multiplatform images, add each platform to be built to this list and buildrunner
        # will use docker buildx to build and provide a single tag containing all architectures specified.
        # Notes:
        #  * buildx may be configured to build some platforms with emulation and therefore builds may take longer with this option specified
        #  * multiplatform builds cannot be used in the buildrunner docker image unless the 'build-registry' global config parameter is specified
        #  * only one of platform or platforms may be specified
        platforms:
          - linux/amd64
          - linux/arm64/v8

        # Specify the build args that should be used when building your image,
        # similar to the --build-args option used by Docker
        buildargs:
          BUILD_ARG_NAME_1: BUILD_ARG_VALUE_1
          BUILD_ARG_NAME_2: BUILD_ARG_VALUE_2

        # Instead of building import the given tar file as a Docker image. If
        # this value is present all other options are ignored and the resulting
        # image is passed to subsequent steps.
        import: path/to/image/archive.tar

        # Specify the secrets that should be used when building your image,
        # similar to the --secret option used by Docker
        # More info about secrets: https://docs.docker.com/build/building/secrets/
        secrets:
          # Example of a secret that is a file
          - id=secret1,src=<path to the secret file>
          # Example of a secret that is an environment variable
          - id=secret2,env=<environment variable name>

.. _Build Secrets:

Build Secrets
=============

Buildrunner supports specifying secrets that should be used when building your image,
similar to the --secret option used by Docker. This is done by adding the ``secrets``
section to the ``build`` section. This is a list of secrets that should be used when
building the image. The string should be in the format of ``id=secret1,src=<location of the file>``
when the secret is a file or ``id=secret2,env=<environment variable name>`` when the secret is an environment variable.
This syntax is the same as the syntax used by Docker to build with secrets.
More info about building with secrets in docker and the syntax of the secret string
see https://docs.docker.com/build/building/secrets/.

In order to use secrets in buildrunner, you need to do the following:

#. Update the buildrunner configuration file
    * Set ``use-legacy-builder`` to ``false`` or add ``platforms`` to the ``build`` section
    * Add the secrets to the ``secrets`` section in the ``build`` section
#. Update the Dockerfile to use the secrets
    * Add the ``--mount`` at the beginning of each RUN command that needs the secret

.. code:: yaml

  use-legacy-builder: false
  steps:
    build-my-container:
      build:
        dockerfile: |
          FROM alpine:latest
          # Using secrets inline
          RUN --mount=type=secret,id=secret1 \
              --mount=type=secret,id=secret2 \
              echo Using secrets in my build - secret1 file located at /run/secrets/secret1 with contents $(cat /run/secrets/secret1) and secret2=$(cat /run/secrets/secret2)
          # Using secrets in environment variables
          RUN --mount=type=secret,id=secret1 \
              --mount=type=secret,id=secret2 \
              SECRET1_FILE=/run/secrets/secret1 \
              SECRET2_VARIABLE=$(cat /run/secrets/secret2) \
              && echo Using secrets in my build - secret1 file located at $SECRET1_FILE with contents $(cat $SECRET1_FILE) and secret2=$SECRET2_VARIABLE
        secrets:
          # Example of a secret that is a file
          - id=secret1,src=examples/build/secrets/secret1.txt
          # Example of a secret that is an environment variable
          - id=secret2,env=SECRET2

.. _Running Containers:

Running Containers (the ``run`` step attribute)
===============================================

The 'run' step attribute is used to create and run a Docker container from a
given image.

There are 2 reasons for running a Docker container within a build:

1. To run another build tool or test framework and collect the resulting
   artifacts
2. To run scripts and operations within an existing image to create a new image
   (similar to how Packer_ creates Docker images)

Buildrunner injects special environment variables and volume mounts into every
run container. The following environment variables are set and available in
every run container:

:``BUILDRUNNER_ARCH``: the architecture of the current device (x86_64, aarch64, etc), equivalent to
                       ``platform.machine()``. Note that the ``--platform`` argument will override this value if
                       specified.
:``BUILDRUNNER_BUILD_NUMBER``: the build number
:``BUILDRUNNER_BUILD_ID``: a unique id identifying the build (includes vcs and build number
                           information), e.g. "main-1791.Ia09cc5.M0-1661374484"
:``BUILDRUNNER_BUILD_DOCKER_TAG``: identical to ``BUILDRUNNER_BUILD_ID`` but formatted for
                                   use as a Docker tag
:``BUILDRUNNER_BUILD_TIME``: the "unix" time or "epoch" time of the build (in seconds)
:``BUILDRUNNER_STEP_ID``: a UUID representing the step
:``BUILDRUNNER_STEP_NAME``: The name of the Buildrunner step
:``BUILDRUNNER_STEPS``: the list of steps manually specified on the command line,
                        defaults to an empty list
:``BUILDRUNNER_INVOKE_USER``: The username of the user that invoked Buildrunner
:``BUILDRUNNER_INVOKE_UID``: The UID of the user that invoked Buildrunner
:``BUILDRUNNER_INVOKE_GROUP``: The group of the user that invoked Buildrunner
:``BUILDRUNNER_INVOKE_GID``: The GID (group ID) of the user that invoked Buildrunner
:``VCSINFO_NAME``: the VCS repository name without a path, "my-project"
:``VCSINFO_BRANCH``: the VCS branch, e.g. "main"
:``VCSINFO_NUMBER``: the VCS commit number, e.g. "1791"
:``VCSINFO_ID``: the VCS commit id, e.g. "a09cc5c407af605b57a0f16b73f896873bb74759"
:``VCSINFO_SHORT_ID``: the VCS short commit id, e.g. "a09cc5c"
:``VCSINFO_RELEASE``: the VCS branch state, .e.g. "1791.Ia09cc5.M0"
:``VCSINFO_MODIFIED``: the last file modification timestamp if local changes have been made and not
                       committed to the source VCS repository, e.g. "1661373883"

The following volumes are created within run containers:

:``/source``: (read-write) maps to a pristine snapshot of the current source tree (build directory)
:``/artifacts``: (read-only) maps to the buildrunner.results directory

The /source volume is actually a mapped volume to a new source container
containing a copy of the build source tree. This container is created from a
docker image containing the entire source tree. Files can be excluded from this
source image by creating a '.buildignore' file in the root of the source tree.
This file follows the same conventions as a .dockerignore file does when
creating Docker images.

The following example shows the different configuration options available in
the run step:

.. code:: yaml

  # Optional buildrunner configuration syntax version
  version: 2.0
  steps:
    my-build-step:
      # Optional step dependency definition to specify which steps need to be processed before this step.
      # The `version` must be present and set to `2.0` or higher for buildrunner to utilize the step dependencies list.
      # An buildrunner error will occur if `depends` is present but `version` is missing or value is lower than `2.0`.
      depends:
        - test-step
        - validation-step

      # This is not supported in the same step as a multiplatform build.
      run:
        # xfail indicates whether the run operation is expected to fail.  The
        # default is false - the operation is expected to succeed.  If xfail
        # is true and the operation succeeds then it will result in a failure.
        xfail: <boolean>

        # A map of additional containers that should be created and linked to
        # the primary run container. These can be used to bring up services
        # (such as databases) that are required to run the step. More details
        # on services below.
        services:
          service-name-1: <service config>
          service-name-2: <service config>

        # The Docker image to run. If empty the image created with the 'build'
        # attribute will be used.
        image: <the Docker image to run>

        # The command(s) to run. If omitted Buildrunner runs the command
        # configured in the Docker image without modification. If provided
        # Buildrunner always sets the container command to a shell, running the
        # given command here within the shell. If both 'cmd' and 'cmds' are
        # present the command in 'cmd' is run before the commands in the 'cmds'
        # list are run.
        cmd: <a command to run>
        cmds:
          - <command one>
          - <command two>

        # A collection of provisioners to run. Provisioners work similar to the
        # way Packer provisioners do and are always run within a shell.
        # When a provisioner is specified Buildrunner always sets the container
        # command to a shell, running the provisioners within the shell.
        # Currently Buildrunner supports shell and salt provisioners.
        provisioners:
          shell: path/to/script.sh | [path/to/script.sh, ARG1, ...]
          salt: <simple salt sls yaml config>

        # The shell to use when specifying the cmd or provisioners attributes.
        # Defaults to /bin/sh. If the cmd and provisioners attributes are not
        # specified this setting has no effect.
        shell: /bin/sh

        # The directory to run commands within. Defaults to /source.
        cwd: /source

        # The user to run commands as. Defaults to the user specified in the
        # Docker image.
        user: <user to run commands as (can be username:group / uid:gid)>

        # The hostname assigned to the run container.
        hostname: <the hostname>

        # Custom dns servers to use in the run container.
        dns:
          - 8.8.8.8
          - 8.8.4.4

        # A custom dns search path to use in the run container.
        dns_search: mydomain.com

        # Add entries to the hosts file
        # The keys are the hostnames.  The values can be either
        # ip addresses or references to service containers.
        extra_hosts:
          "www1.test.com": "192.168.0.1"
          "www2.test.com": "192.168.0.2"

        # A map specifying additional environment variables to be injected into
        # the container. Keys are the variable names and values are variable
        # values.
        env:
          ENV_VARIABLE_ONE: value1
          ENV_VARIABLE_TWO: value2

        # A map specifying files that should be injected into the container.
        # The map key is the alias referencing a given file (as configured in
        # the "local-files" section of the global configuration file) or a
        # relative path to a file/directory in the build directory. The value
        # is the path the given file should be mounted at within the container.
        files:
          namespaced.file.alias1: "/path/to/readonly/file/or/dir"
          namespaced.file.alias2: "/path/to/readwrite/file/or/dir:rw"
          build/dir/file: "/path/to/build/dir/file"

        # A map specifying cache directories that are stored as archive files on the
        # host system as `local cache key` and extracted as a directory in
        # the container named `docker path`. The cache directories are maintained
        # between builds and can be used to store files, such as downloaded
        # dependencies, to speed up builds.
        # Caches can be shared between any builds or projects on the system
        # as the names are not prefixed with any project-specific information.
        # Caches should be treated as ephemeral and should only store items
        # that can be obtained/generated by subsequent builds.
        #
        # Two formats are supported when defining caches.
        # 1) RECOMMENDED
        #    <docker path>:
        #      - <local cache key A>
        #      - <local cache key B>
        #
        #    Restore Cache:
        #      This format allows for prefix matching. The order of the list dictates the
        #      order which should be searched in the local system cache location.
        #      When an item isn't found it will search for archive files which prefix matches
        #      the item in the list. If more than one archive file is matched for a prefix
        #      the archive file most recently modified will be used. If there is no
        #      matching archive file then nothing will be restored in the docker container.
        #
        #    Save Cache:
        #      The first local cache key in the list is used for the name of the local
        #      cache archive file.
        #
        # 2) <local cache key>: <docker path> (backwards compatible with older caching method, but more limited)
        #
        caches:
          # Recommended format.
          <docker path>:
            - <local cache key A>
            - <local cache key B>

          "/root/.m2/repository":
            # Buildrunner will look for a cache that matches this cache key/prefix,
            # typically the first key should be the most specific as it is the closest match
            # Note that this first key will also be used to save the cache for use across builds or projects
            - m2repo-{{ checksum("pom.xml", "subproj/pom.xml") }}
            # If the first cache key is not found in the caches, use this prefix to look for a cache that may not
            # be an exact match, but may still be close and not require as much downloading of dependencies, etc
            # Note that this may match across any cache done by any build on the same system, so it may be wise to
            # use a unique prefix for any number of builds that have a similar dependency tree, etc
            - m2repo-
            # If no cache is found, nothing will be extracted and the application will need to rebuild the cache

          # Backwards compatible format. Not recommended for future or updated configurations.
          <local cache key>: <docker path>
          maven: "/root/.m2/repository"

        # A map specifying ports to expose, this is only used when the
        # --publish-ports parameter is passed to buildrunner
        ports:
          <container port>: <host port>

        # A list specifying service containers (see below) whose exposed
        # volumes should be mapped into the run container's file system.
        # An exposed volume is one created by the volume Dockerfile command.
        # See https://docs.docker.com/engine/reference/builder/#volume for more
        # details regarding the volume Dockerfile command.
        volumes_from:
          - my-service-container

        # A list specifying ssh keys that should be injected into the container
        # via an ssh agent. The list should specify the ssh key aliases (as
        # configured in the "ssh-keys" section of the global configuration
        # file) that buildrunner should inject into the container. Buildrunner
        # injects the keys by mounting a ssh-agent socket and setting the
        # appropriate environment variable, meaning that the private key itself
        # is never available inside the container.
        ssh-keys:
          - my_ssh_key_alias

        # A map specifying the artifacts that should be archived for the step.
        # The keys in the map specify glob patterns of files to archive. If a
        # value is present it should be a map of additional properties that
        # should be added to the build artifacts.json file. The artifacts.json
        # file can be used to publish artifacts to another system (such as
        # Gauntlet) with the accompanying metadata. By default artifacts will be
        # listed in the artifacts.json file; this can be disabled by adding the
        # ``push`` property and set it to false.
        #
        # When archiving *directories* special properties can be set to change
        # the behavior of the archiver.  Directories by default are archived as
        # gzip'ed TARs.  The compression can be changed by setting the
        # ``compression`` property to one of the below-listed values.  The
        # archive type can be changed by setting the property ``type:zip``.
        # When a zip archive is requested then the ``compression`` property is
        # ignored.  If the directory tree should be gathered verbatim without
        # archiving then the property ``format:uncompressed`` can be used.
        #
        # Rename allows for specifying exact matches to rename for files and
        # compressed directories. Wildcard (*) matches is not supported.
        #
        # NOTE: Artifacts can only be archived from the /source directory using
        # a relative path or a full path. Files outside of this directory will
        # fail to be archived.
        artifacts:
          artifacts/to/archive/*:
            [format: uncompressed]
            [type: tar|zip]
            [compression: gz|bz2|xz|lzma|lzip|lzop|z]
            [push: true|false]
            [rename: new-name]
            property1: value1
            property2: value2

        # Whether or not to pull the image from upstream prior to running
        # the step.  This is almost always desirable, as it ensures the
        # most up to date source image.
        # NOTE: If the image was created from a 'push' or 'commit' earlier in
        #       this ``buildrunner.yaml`` then this will default to false
        pull: true/false # (default changes depending on if the
                         # image was created via buildrunner or not)

        # Specify a different platform architecture when pulling and running images.
        # This is useful if you are running an image that was built for a different architecture
        # than what buildrunner is running on, such as using a linux/arm64/v8 Apple M1 architecture
        # development machine to run or test an image built for linux/amd64 architecture.
        platform: linux/amd64
        <or>
        platform: linux/arm64/v8 # an apple m1 architecture

        # systemd does not play well with docker typically, but you can
        # use this setting to tell buildrunner to set the necessary docker
        # flags to get systemd to work properly:
        # - /usr/sbin/init needs to run as pid 1
        # - /sys/fs/cgroup needs to be mounted as readonly
        #   (-v /sys/fs/cgroup:/sys/fs/cgroup:ro)
        # - The security setting seccomp=unconfined must be set
        #   (--security-opt seccomp=unconfined)
        # If this is ommitted, the image will be inspected for the label
        # 'BUILDRUNNER_SYSTEMD'.
        # If found, systemd=true will be assumed.
        systemd: true/false
        # (Ignored when systemd is not enabled)
        # For cgroup v2, a read-write mount for /sys/fs/cgroup is required as well as a tmpfs mounted at /run, and
        # this flag enables this behavior
        # If this is omitted, the image will be inspected for the label
        # 'BUILDRUNNER_SYSTEMD_CGROUP2' and that value will be used instead.
        systemd_cgroup2: true/false

        # Docker supports certain kernel capabilities, like 'SYS_ADMIN'.
        # see https://goo.gl/gTQrqW for more infromation on setting these.
        cap_add: 'SYS_ADMIN'
        <or>
        cap_add:
          - 'SYS_ADMIN'
          - 'SYS_RAWIO'

        # Docker can run in a privileged mode. This allows access to all devices
        # on the host. Using privileged is rare, but there are good use cases
        # for this feature. see https://goo.gl/gTQrqW for more infromation on
        # setting these.
        # Default: false
        privileged: true/false

        # The post-build attribute commits the resulting run container as an
        # image and allows additional Docker build processing to occur. This is
        # useful for adding Docker configuration, such as EXPOSE and CMD
        # instructions, when building an image via the run task that cannot be
        # done without running a Docker build. The post-build attribute
        # functions the same way as the 'build' step attribute does, except
        # that it prepends the committed run container image to the provided
        # Dockerfile ('FROM <image>\n').
        post-build: path/to/build/context
        <or>
        post-build:
          dockerfile: |
            EXPOSE 80
            CMD /runserver.sh

        # A list of container names or labels created within any run container
        # that buildrunner should clean up.  (Use if you call
        # 'docker run --name <name>' or 'docker run --label <label>' within a run container.)
        containers:
          - container1
          - container2

Service Containers
------------------

Service containers allow you to create and start additional containers that
are linked to the primary build container. This is useful, for instance, if
your unit or integration tests require an outside service, such as a database
service. Service containers are instantiated in the order they are listed.
Service containers have the same injected environment variables and volume
mounts as build containers do, but the /source mount is read-only.

The following example shows the different configuration options available
within service container configuration:

.. code:: yaml

  steps:
    my-build-step:
      run:
        services:
          my-service-container:
            # The 'build' attribute functions the same way that the step
            # 'build' attribute does. The only difference is that the image
            # produced by a service container build attribute cannot be pushed
            # to a remote repository.
            build: <path/to/build/context or map>

            # The pre-built image to base the container on. The 'build' and
            # 'image' attributes are mutually exclusive in the service
            # container context.
            image: <the Docker image to run>

            # The command to run. If ommitted Buildrunner runs the command
            # configured in the Docker image without modification. If provided
            # Buildrunner always sets the container command to a shell, running
            # the given command here within the shell.
            cmd: <a command to run>

            # A collection of provisioners to run. Provisioners work similar to
            # the way Packer provisioners do and are always run within a shell.
            # When a provisioner is specified Buildrunner always sets the
            # container command to a shell, running the provisioners within the
            # shell. Currently Buildrunner supports shell and salt
            # provisioners.
            provisioners:
              shell: path/to/script.sh
              salt: <simple salt sls yaml config>

            # The shell to use when specifying the cmd or provisioners
            # attributes. Defaults to /bin/sh. If the cmd and provisioners
            # attributes are not specified this setting has no effect.
            shell: /bin/sh

            # The directory to run commands within. Defaults to /source.
            cwd: /source

            # The user to run commands as. Defaults to the user specified in
            # the Docker image.
            user: <user to run commands as (can be username:group / uid:gid)>

            # The hostname assigned to the service container.
            hostname: <the hostname>

            # Custom dns servers to use in the service container.
            dns:
              - 8.8.8.8
              - 8.8.4.4

            # A custom dns search path to use in the service container.
            dns_search: mydomain.com

            # Add entries to the hosts file
            # The keys are the hostnames.  The values can be either
            # ip addresses or references to other service containers.
            extra_hosts:
              "www1.test.com": "192.168.0.1"
              "www2.test.com": "192.168.0.2"

            # A map specifying additional environment variables to be injected
            # into the container. Keys are the variable names and values are
            # variable values.
            env:
              ENV_VARIABLE_ONE: value1
              ENV_VARIABLE_TWO: value2

            # A map specifying files that should be injected into the container.
            # The map key is the alias referencing a given file (as configured in
            # the "local-files" section of the global configuration file) or a
            # relative path to a file/directory in the build directory. The value
            # is the path the given file should be mounted at within the container.
            files:
              namespaced.file.alias1: "/path/to/readonly/file/or/dir"
              namespaced.file.alias2: "/path/to/readwrite/file/or/dir:rw"
              build/dir/file: "/path/to/build/dir/file"

            # A list specifying other service containers whose exposed volumes
            # should be mapped into this service container's file system. Any
            # service containers in this list must be defined before this
            # container is.
            # An exposed volume is one created by the volume Dockerfile command.
            # See https://docs.docker.com/engine/reference/builder/#volume for more
            # details regarding the volume Dockerfile command.
            volumes_from:
              - my-service-container

            # A map specifying ports to expose and link within other containers
            # within the step.
            ports:
              <container port>: <host port>

            # Whether or not to pull the image from upstream prior to running
            # the step.  This is almost always desirable, as it ensures the
            # most up to date source image.  There are situations, however, when
            # this can be set to false as an optimization.  For example, if a
            # container is built at the beginning of a buildrunner file and then
            # used repeatedly.  In this case, it is clear that the cached version
            # is appropriate and we don't need to check upstream for changes.
            pull: true/false (defaults to true)

            # See above
            systemd: