guix-docker-images/README.md

MetaCall Guix

Docker image for using Guix in a CI/CD environment.

How to use it

This image encapsulates the Guix daemon. For now, Guix does not have a daemonless option, so packaging it into a Docker image has some implications. The Guix daemon needs to fork, and forking a process during build phase is not allowed, so we have to work with it in a different way. There are two options:

1. Running the build with Docker, using the --privileged flag and commiting the result on each step. For example, imagine we have the following Dockerfile:

   FROM metacall/guix:latest AS example
   
   # Copy some dependencies
   COPY . .
   

   Now we can build the image metacall/example with docker run + commit:

   # Build the base image
   docker build -t metacall/example -f Dockerfile .
   # Run a guix pull
   docker run --privileged --name tmp metacall/example sh -c 'guix pull'
   # Commit changes
   docker commit tmp metacall/new-image && docker rm -f tmp
   # Install some package
   docker run --privileged --name tmp metacall/example sh -c 'guix package -i guile'
   # Commit changes
   docker commit tmp metacall/example && docker rm -f tmp
   # Push the final image
   docker push metacall/example
   

   A complete working example used in production can be found here: https://github.com/metacall/distributable

2. Running the build with BuildKit using the buildx extension for Docker (like how it is done in this repository: e9a0e791af/Dockerfile (L73)). BuildKit allows to pass extra arguments to the RUN command in the Dockerfile. With the --security=insecure flag we can allow Docker to fork while it is building. The previous example can be transformed into this:

   FROM metacall/guix:latest AS example
   
   # Copy some dependencies
   COPY . .
   
   # Run guix pull and install dependencies
   RUN --security=insecure sh -c '/entry-point.sh guix pull' \
       && sh -c '/entry-point.sh guix package -i guile'
   

   For building this image we need Docker v19.03 or superior and the buildx plugin:

   # Install the buildx plugin
   docker build --platform=local -o . git://github.com/docker/buildx
   mkdir -p ~/.docker/cli-plugins/
   mv buildx ~/.docker/cli-plugins/docker-buildx
   

   If you have it already installed, we need to create an insecure builder (this must be run only once):

   # Create an insecure builder
   docker buildx create --use --name insecure-builder --buildkitd-flags '--allow-insecure-entitlement security.insecure'
   

   Finally, for building the Dockerfile with the already created insecure builder, we have to run this command:

   # Build and push the image with buildx
   docker buildx build -t metacall/example -o type=registry --allow security.insecure .