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apko: apk-based OCI image builder

Build and publish OCI container images built from apk packages.

apko has the following key features:

  • Fully reproducible by default. Run apko twice and you will get exactly the same binary.
  • Fast. apko aims to build images in ms.
  • Small. apko generated images only contain what's needed by the application, in the style of distroless.
  • SBOM Support. apko produces a Software Bill of Materials (SBOM) for images, detailing all the packages inside.
  • Services. apko supports using the s6 supervision suite to run multiple processes in a container without reaping or signalling issues.

Please note that apko is a work in progress and details are subject to change!

Installation

apko has a dependency on apk-tools. If you're not running on Alpine Linux or another apk-based distribution, the quickest way to get apko running is to use the OCI Container (Docker) image:

docker run distroless.dev/apko version
     _      ____    _  __   ___
    / \    |  _ \  | |/ /  / _ \
   / _ \   | |_) | | ' /  | | | |
  / ___ \  |  __/  | . \  | |_| |
 /_/   \_\ |_|     |_|\_\  \___/
apko

GitVersion:    v0.5.0-67-g9084217
GitCommit:     9084217c907232b8c0bb87fd99c3e65eaa581a5b
GitTreeState:  clean
BuildDate:     '1970-01-01T00:00:00Z'
GoVersion:     go1.18.5
Compiler:      gc
Platform:      linux/amd64

To use the examples, you'll generally want to mount your current directory into the container e.g:

docker run -v "$PWD":/work distroless.dev/apko build examples/alpine-base.yaml apko-alpine:edge apko-alpine.tar

These examples use Docker, but should also work with other runtimes such as podman.

Alternatively, if you're on a Mac, you can use Lima to run an Alpine Linux VM.

Quickstart

An apko file for building an Alpine base image looks like this:

contents:
  repositories:
    - https://dl-cdn.alpinelinux.org/alpine/edge/main
  packages:
    - alpine-base

entrypoint:
  command: /bin/sh -l

# optional environment configuration
environment:
  PATH: /usr/sbin:/sbin:/usr/bin:/bin

We can build this with apko from any environment with apk tooling:

apko build examples/alpine-base.yaml apko-alpine:test apko-alpine.tar
...
2022/04/08 13:22:31 apko (aarch64): generating SBOM
2022/04/08 13:22:31 building OCI image from layer '/tmp/apko-3027985148.tar.gz'
2022/04/08 13:22:31 OCI layer digest: sha256:ba034c07d0945abf6caa46fe05268d2375e4209e169ff7fdd34d40cf4e5f2dd6
2022/04/08 13:22:31 OCI layer diffID: sha256:9b4ab6bb8831352b25c4bd21ee8259d1f3b2776deec573733291d71a390157bb
2022/04/08 13:22:31 output OCI image file to apko-alpine.tar

or, with Docker:

docker run -v "$PWD":/work distroless.dev/apko build examples/alpine-base.yaml apko-alpine:test apko-alpine.tar

You can then load the generated tar image into a Docker environment:

docker load < apko-alpine.tar
Loaded image: apko-alpine:test
docker run -it apko-alpine:test
e289dc84c4ad:/# echo boo!
boo!

You can also publish the image directly to a registry:

apko publish examples/alpine-base.yaml myrepo/alpine-apko:test

See the docs for details of the file format and the examples directory for more, err, examples!

Debugging apko Builds

To include debug-level information on apko builds, add --debug to your build command:

docker run --rm -v ${PWD}:/work distroless.dev/apko build --debug \
  apko.yaml hello-minicli:test hello-minicli.tar \
  -k melange.rsa.pub

Why

apko was created by Chainguard, who require secure and reproducible container images for their tooling. Speed is also a critical factor; Chainguard require images to be rebuilt constantly in response to new versions and patches.

The design of apko is heavily influenced by the ko and distroless projects.

Declarative Nature

By design, apko doesn't support an equivalent of RUN statements in Dockerfiles. This means apko files are fully declarative and allows apko to make stronger statements about the contents of images. In particular, apko images are fully bitwise reproducible and can generate SBOMs covering their complete contents.

In order to install bespoke tooling or applications into an image, they must first be packaged into an apk. This can be done with apko's sister tool melange.

The combination of melange and apko cover the vast majority of use cases when building container images. In the cases where they are not a good fit, our recommendation is to build a base image with apko and melange, then use traditional tooling such as Dockerfiles for the final step.

Related work and resources

The melange project is designed to produce apk packages to be used in apko.

The ko project builds Go projects from source in a similar manner to apko.

The kontain.me service creates fresh container images on demand using different forms of declarative configuration (including ko and apko).