Bazel Container Image Rules

Bazel CI

Status

🚨 rules_docker is no longer maintained and deprecated. Please see rules_oci for a better designed and maintained alternative.

Basic Rules

• container_image (example)
• container_bundle (example)
• container_import
• container_load
• container_pull (example)
• container_push (example)

These rules used to be docker_build, docker_push, etc. and the aliases for these (mostly) legacy names still exist largely for backwards-compatibility. We also have early-stage oci_image, oci_push, etc. aliases for folks that enjoy the consistency of a consistent rule prefix. The only place the format-specific names currently do any more than alias things is in foo_push, where they also specify the appropriate format as which to publish the image.

Overview

This repository contains a set of rules for pulling down base images, augmenting them with build artifacts and assets, and publishing those images. These rules do not require / use Docker for pulling, building, or pushing images. This means:

• They can be used to develop Docker containers on OSX without boot2docker or docker-machine installed. Note use of these rules on Windows is currently not supported.
• They do not require root access on your workstation.

Also, unlike traditional container builds (e.g. Dockerfile), the Docker images produced by container_image are deterministic / reproducible.

To get started with building Docker images, check out the examples that build the same images using both rules_docker and a Dockerfile.

NOTE: container_push and container_pull make use of google/go-containerregistry for registry interactions.

Language Rules

• py_image (signature)
• py3_image (signature)
• nodejs_image (usage)
• java_image (signature)
• war_image (signature)
• scala_image (signature)
• groovy_image (signature)
• cc_image (signature)
• go_image (signature)
• rust_image (signature)
• d_image (signature)

It is notable that: cc_image, go_image, rust_image, and d_image also allow you to specify an external binary target.

Docker Rules

This repo now includes rules that provide additional functionality to install packages and run commands inside docker containers. These rules, however, require a docker binary is present and properly configured. These rules include:

• Package manager rules: rules to install apt-get packages.
• Docker run rules: rules to run commands inside docker containers.

Overview

In addition to low-level rules for building containers, this repository provides a set of higher-level rules for containerizing applications. The idea behind these rules is to make containerizing an application built via a lang_binary rule as simple as changing it to lang_image.

By default these higher level rules make use of the distroless language runtimes, but these can be overridden via the base="..." attribute (e.g. with a container_pull or container_image target).

Note also that these rules do not expose any docker related attributes. If you need to add a custom env or symlink to a lang_image, you must use container_image targets for this purpose. Specifically, you can use as base for your lang_image target a container_image target that adds e.g., custom env or symlink. Please see <a href=#go_image-custom-base>go_image (custom base)</a> for an example.

Setup

Add the following to your WORKSPACE file to add the external repositories:

load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

http_archive(
  # Get copy paste instructions for the http_archive attributes from the
  # release notes at https://github.com/bazelbuild/rules_docker/releases
)

# OPTIONAL: Call this to override the default docker toolchain configuration.
# This call should be placed BEFORE the call to "container_repositories" below
# to actually override the default toolchain configuration.
# Note this is only required if you actually want to call
# docker_toolchain_configure with a custom attr; please read the toolchains
# docs in /toolchains/docker/ before blindly adding this to your WORKSPACE.
# BEGIN OPTIONAL segment:
load("@io_bazel_rules_docker//toolchains/docker:toolchain.bzl",
    docker_toolchain_configure="toolchain_configure"
)
docker_toolchain_configure(
  name = "docker_config",
  # OPTIONAL: Bazel target for the build_tar tool, must be compatible with build_tar.py
  build_tar_target="<enter absolute path (i.e., must start with repo name @...//:...) to an executable build_tar target>",
  # OPTIONAL: Path to a directory which has a custom docker client config.json.
  # See https://docs.docker.com/engine/reference/commandline/cli/#configuration-files
  # for more details.
  client_config="<enter Bazel label to your docker config.json here>",
  # OPTIONAL: Path to the docker binary.
  # Should be set explicitly for remote execution.
  docker_path="<enter absolute path to the docker binary (in the remote exec env) here>",
  # OPTIONAL: Path to the gzip binary.
  gzip_path="<enter absolute path to the gzip binary (in the remote exec env) here>",
  # OPTIONAL: Bazel target for the gzip tool.
  gzip_target="<enter absolute path (i.e., must start with repo name @...//:...) to an executable gzip target>",
  # OPTIONAL: Path to the xz binary.
  # Should be set explicitly for remote execution.
  xz_path="<enter absolute path to the xz binary (in the remote exec env) here>",
  # OPTIONAL: Bazel target for the xz tool.
  # Either xz_path or xz_target should be set explicitly for remote execution.
  xz_target="<enter absolute path (i.e., must start with repo name @...//:...) to an executable xz target>",
  # OPTIONAL: List of additional flags to pass to the docker command.
  docker_flags = [
    "--tls",
    "--log-level=info",
  ],

)
# End of OPTIONAL segment.

load(
    "@io_bazel_rules_docker//repositories:repositories.bzl",
    container_repositories = "repositories",
)
container_repositories()

load("@io_bazel_rules_docker//repositories:deps.bzl", container_deps = "deps")

container_deps()

load(
    "@io_bazel_rules_docker//container:container.bzl",
    "container_pull",
)

container_pull(
  name = "java_base",
  registry = "gcr.io",
  repository = "distroless/java",
  # 'tag' is also supported, but digest is encouraged for reproducibility.
  digest = "sha256:deadbeef",
)

Known Issues

• Bazel does not deal well with diamond dependencies.

If the repositories that are imported by container_repositories() have already been imported (at a different version) by other rules you called in your WORKSPACE, which are placed above the call to container_repositories(), arbitrary errors might occur. If you get errors related to external repositories, you will likely not be able to use container_repositories() and will have to import directly in your WORKSPACE all the required dependencies (see the most up to date impl of container_repositories() for details).

• ImportError: No module named moves.urllib.parse

This is an example of an error due to a diamond dependency. If you get this error, make sure to import rules_docker before other libraries, so that six can be patched properly.

See https://github.com/bazelbuild/rules_docker/issues/1022 for more details.

• Ensure your project has a BUILD or BUILD.bazel file at the top level. This can be a blank file if necessary. Otherwise you might see an error that looks like:

Unable to load package for //:WORKSPACE: BUILD file not found in any of the following directories.

• rules_docker uses transitions to build your containers using toolchains the correct architecture and operating system. If you run into issues with toolchain resolutions, you can disable this behaviour, by adding this to your .bazelrc:

build --@io_bazel_rules_docker//transitions:enable=false

Using with Docker locally.

Suppose you have a container_image target //my/image:helloworld:

container_image(
    name = "helloworld",
    ...
)

You can load this into your local Docker client by running: bazel run my/image:helloworld.

For the lang_image targets, this will also run the container using docker run to maximize compatibility with lang_binary rules.

Arguments to this command are forwarded to docker, meaning the command

bazel run my/image:helloworld -- -p 8080:80 -- arg0

performs the following steps:

• load the my/image:helloworld target into your local Docker client
• start a container using this image where arg0 is passed to the image entrypoint
• port forward 8080 on the host to port 80 on the container, as per docker run documentation

You can suppress this behavior by passing the single flag: bazel run :foo -- --norun

Alternatively, you can build a docker load compatible bundle with: bazel build my/image:helloworld.tar. This will produce a tar file in your bazel-out directory that can be loaded into your local Docker client. Building this target can be expensive for large images. You will first need to query the ouput file location.

TARBALL_LOCATION=$(bazel cquery my/image:helloworld.tar \
    --output starlark \
    --starlark:expr="target.files.to_list()[0].path")
docker load -i $TARBALL_LOCATION

These work with both container_image, container_bundle, and the lang_image rules. For everything except container_bundle, the image name will be bazel/my/image:helloworld. The container_bundle rule will apply the tags you have specified.

Authentication

You can use these rules to access private images using standard Docker authentication methods. e.g. to utilize the Google Container Registry. See here for authentication methods.

See also:

• Amazon ECR Docker Credential Helper
• Azure Docker Credential Helper

Once you've setup your docker client configuration, see here for an example of how to use container_pull with custom docker authentication credentials and here for an example of how to use container_push with custom docker authentication credentials.

Varying image names

A common request from folks using container_push, container_bundle, or container_image is to be able to vary the tag that is pushed or embedded. There are two options at present for doing this.

Stamping

The first option is to use stamping. Stamping is enabled when bazel is run with --stamp. This enables replacements in stamp-aware attributes. A python format placeholder (e.g. {BUILD_USER}) is replaced by the value of the corresponding workspace-status variable.

# A common pattern when users want to avoid trampling
# on each other's images during development.
container_push(
  name = "publish",
  format = "Docker",

  # Any of these components may have variables.
  registry = "gcr.io",
  repository = "my-project/my-image",
  # This will be replaced with the current user when built with --stamp
  tag = "{BUILD_USER}",
)

Rules that are sensitive to stamping can also be forced to stamp or non-stamp mode irrespective of the --stamp flag to Bazel. Use the build_context_data rule to make a target that provides StampSettingInfo, and pass this to the build_context_data attribute.

The next natural question is: "Well what variables can I use?" This option consumes the workspace-status variables Bazel defines in bazel-out/stable-status.txt and bazel-out/volatile-status.txt.

Note that changes to the stable-status file cause a rebuild of the action, while volatile-status does not.

You can add more stamp variables via --workspace_status_command, see the bazel docs. A common example is to provide the current git SHA, with --workspace_status_command="echo STABLE_GIT_SHA $(git rev-parse HEAD)"

That flag is typically passed in the .bazelrc file, see for example .bazelrc in kubernetes.

Make variables

The second option is to employ Makefile-style variables:

container_bundle(
  name = "bundle",

  images = {
    "gcr.io/$(project)/frontend:latest": "//frontend:image",
    "gcr.io/$(project)/backend:latest": "//backend:image",
  }
)

These variables are specified on the CLI using:

   bazel build --define project=blah //path/to:bundle

Debugging lang_image rules

By default the lang_image rules use the distroless base runtime images, which are optimized to be the minimal set of things your application needs at runtime. That can make debugging these containers difficult because they lack even a basic shell for exploring the filesystem.

To address this, we publish variants of the distroless runtime images tagged :debug, which are the exact-same images, but with additions such as busybox to make debugging easier.

For example (in this repo):

$ bazel run -c dbg testdata:go_image
...
INFO: Build completed successfully, 5 total actions

INFO: Running command line: bazel-bin/testdata/go_image
Loaded image ID: sha256:9c5c2167a1db080a64b5b401b43b3c5cdabb265b26cf7a60aabe04a20da79e24
Tagging 9c5c2167a1db080a64b5b401b43b3c5cdabb265b26cf7a60aabe04a20da79e24 as bazel/testdata:go_image
Hello, world!

$ docker run -ti --rm --entrypoint=sh bazel/testdata:go_image -c "echo Hello, busybox."
Hello, busybox.

Examples

container_image

container_image(
    name = "app",
    # References container_pull from WORKSPACE (above)
    base = "@java_base//image",
    files = ["//java/com/example/app:Hello_deploy.jar"],
    cmd = ["Hello_deploy.jar"]
)

Hint: if you want to put files in specific directories inside the image use <a href="https://docs.bazel.build/versions/master/be/pkg.html">pkg_tar rule</a> to create the desired directory structure and pass that to container_image via tars attribute. Note you might need to set strip_prefix = "." or strip_prefix = "{some directory}" in your rule for the files to not be flattened. See <a href="https://github.com/bazelbuild/bazel/issues/2176">Bazel upstream issue 2176</a> and <a href="https://github.com/bazelbuild/rules_docker/issues/317">rules_docker issue 317</a> for more details.

cc_image

To use cc_image, add the following to WORKSPACE:

load(
    "@io_bazel_rules_docker//repositories:repositories.bzl",
    container_repositories = "repositories",
)

container_repositories()

load(