Bazel rules for OCI containers

This is a "barebones" alternative to rules_docker.

A lot of companies have already done a successful migration from rules_docker. Please let us know about yours on our adoption discussion! #299

We start from first principles and avoided some pitfalls we learned in maintaining that repo:

• 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.

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

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, and how to migrate from the language-specific rules in rules_docker.

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

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 memory hungry as it stores blobs in memory, leading to high memory usage. However it supports both OCI and Docker formats which is quite useful for using Docker images pulled from the registries such as DockerHub.

Public API Docs

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 Pulls image layers using Bazel's downloader.
• 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 or oci_tarball target.