Bazel rules for OCI container images

Bazel rules based on the Open Containers Initiative: https://opencontainers.org/

Please let us know about your success stories on our adoption discussion! bazel-contrib#299

Need help? This ruleset has support provided by https://aspect.dev.

Comparison with rules_docker

This ruleset is not intended as a complete replacement for rules_docker! Many use cases can be accomodated, and we know that many users have completely replaced rules_docker. You can find a migration guide at https://docs.aspect.build/guides/rules_oci_migration. However, some other use cases such as container_run_and_* rules have no equivalent.

rules_docker was largely unmaintained for 18 months, and as of October 2023 it has been archived. See bazelbuild/rules_docker#2038. You might still decide to use rules_docker, and perhaps even sign up as a maintainer so that it may be un-archived.

We started from first principles and avoided some pitfalls we learned from rules_docker:

• Use a toolchain consisting of off-the-shelf, pre-built layer and container manipulation tools.
• Don't write language-specific rules, as we cannot be experts on all languages, nor can users deal with the versioning issues that come with dependencies we would be forced to take on the rules for those languages.
• Don't be docker-specific, now that it has a commercial license and other container runtimes exist (podman for example).
• Use our toolchain hermetically: don't assume there is a docker pre-installed on the machine.
• Keep a tight complexity budget for the project so we are able to commit to effective maintenance.

Installation

See the install instructions on the release notes: https://github.com/bazel-contrib/rules_oci/releases

To use a commit rather than a release, you can point at any SHA of the repo.

With bzlmod, you can use archive_override or git_override. For WORKSPACE, you modify the http_archive call; for example to use commit abc123 with a WORKSPACE file:

1. Replace url = "https://github.com/bazel-contrib/rules_oci/releases/download/v0.1.0/rules_oci-v0.1.0.tar.gz" with a GitHub-provided source archive like url = "https://github.com/bazel-contrib/rules_oci/archive/abc123.tar.gz"
2. Replace strip_prefix = "rules_oci-0.1.0" with strip_prefix = "rules_oci-abc123"
3. Update the sha256. The easiest way to do this is to comment out the line, then Bazel will print a message with the correct value.

Note that GitHub source archives don't have a strong guarantee on the sha256 stability, see https://github.blog/2023-02-21-update-on-the-future-stability-of-source-code-archives-and-hashes

Usage

rules_oci does not contain language-specific rules, but we do have limited documentation on how to accomplish typical tasks.

• C/C++
• Go
• Java
• JavaScript
• Python
• Rust
• Scala
• WASM (see https://docs.docker.com/desktop/wasm/)
• Static Content (such as a html/javascript frontend)

Note

Your language not listed above? Please contribute engineering resources or financially through our Sponsor link!

There are some generic examples of usage in the examples folder. Note that these examples rely on the setup code in the /WORKSPACE file in the root of this repo.

Choosing between zot or crane as the local registry

rules_oci supports two different registry implementation for the temporary storage within actions spawned by bazel.

1. By default we recommend using zot as it stores blobs on disk, however it doesn't support Docker-format images.
2. crane is a better alternative as it supports both OCI and Docker formats which is required to make images with Docker media types work. However, it might not support everything that zot does.

Public API Docs

Build Base images

• Alpine: we recommend https://github.com/chainguard-dev/rules_apko to install apk packages using Chainguard's apko.
• Debian: The apt-get utility installs .deb files, which are already archives that may be used directly as image layers. See /examples/deb in this repository. This solution is incomplete since apt does some other tasks which you may need. See bazel-contrib#375 for details.
• RHEL/CentOS/Amazon Linux: we don't have any support for this yet. Please consider donating to the project!

Construct image layers

• oci_image Build an OCI compatible container image.
• oci_image_index Build a multi-architecture OCI compatible container image.
• oci_tarball Creates tarball from oci_image that can be loaded by runtimes.

Pull and Push

• oci_pull Pull image layers using Bazel's downloader. Falls back to using curl in some cases.
• oci_push Push an oci_image or oci_image_index to a remote registry.

Testing

• We recommend container_structure_test to run tests against an oci_image target (with driver="docker") or an oci_tarball target (with driver="tar").

Signing

Warning

Signing images is a developer preview, not part of public API yet.

• cosign_sign: Sign an oci_image using cosign binary at a remote registry.
• cosign_attest Add an attachment to an oci_image at a remote registry using cosign.