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Generate various Docker ocaml images
OCaml Dockerfile Makefile
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Status: experimental

This is an OCurrent pipeline that builds Docker images for OCaml, for various combinations of Linux distribution, OCaml version and architecture.

The resulting images can be run as e.g.

docker run --rm -it ocurrent/opam:debian-10-ocaml-4.08

(this is a temporary location and will likely change in future)

These images are very similar to the ones currently available as ocaml/opam2, and use the same scripts from avsm/ocaml-dockerfile. However, they are much smaller because each image only includes one OCaml compiler.

Each image includes two Dockerfiles showing how it was made:

  • /Dockerfile.opam is the first stage, which just installs the opam binary.
  • /Dockerfile.ocaml builds on the first stage by installing a particular opam switch.

The rest of this README is about working on the build pipeline.

Testing locally

To see the pipeline, clone the repository and run it:

git clone --recursive
cd docker-base-images
opam pin -yn ./ocurrent
opam pin -yn ./ocaml-dockerfile
opam pin -yn .
opam -y depext -y base-images
opam install -y --deps-only base-images
dune exec -- ./src/base_images.exe --confirm harmless

Running with --confirm harmless means that it will just show what it plans to do without trying to run any jobs yet. You should see:

Password file "/run/secrets/ocurrent-hub" not found; images will not be pushed to hub
   current_web [INFO] Starting web server: (TCP (Port 8080))

If you now browse to you can see the (rather large!) build pipeline. It should look something like this (but less green initially):

It starts by cloning opam-repository, then creates images by installing an opam binary and a copy of opam-repository for many Linux distributions and architectures.

These architecture-specific images get pushed to a staging repository on Docker Hub, and are then combined into a single multi-arch image.

Separately, the architecture-specific base images are also used to create more images - one for each supported OCaml compiler version. These images are also pushed to a staging repository and then combined into multi-arch images.

If you use the web user interface to set the confirmation threshold to >= Average, it will clone opam-repository. However, before going further you will need to configure the builders.

The configuration is in You can change the repositories to which the images will be pushed here, and provide a way to get your Hub password. For testing, you'll probably want to uncomment the lines near the bottom to restrict the build to just a few combinations.

The default configuration assumes that your local Docker engine builds X86_64 images and that you have set up Docker contexts arm64 and ppc64 for those architectures. To set up a Docker context, use e.g. docker -H ssh:// context create arm64.

The pipeline is defined in This includes the Dockerfile definitions used to build the images.

Once running with your chosen configuration, you can use the web UI to raise (or remove) the confirmation threshold.

The real deployment

The builder currently runs on The configuration is in stack.yml. To update it:

docker --context stack deploy -c stack.yml base-images

If you are doing your own deployment, you will need to provide some secrets (using docker secret create):

  • ocurrent-hub is the Docker Hub password, which is used to push the images.
  • ocurrent-ssh-key is needed for any builders that are accessed over SSH.
  • ocurrent-tls-key is needed for any builders that are accessed over TLS.
  • ocurrent-slack-endpoint allows pushing status messages to a Slack channel.
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