Run docker-compose without images with Nix

Wait, what?

With Arion you can fire up containers without creating images for each service. Instead, it uses a mostly empty image, sort of like a base image, and makes the host's Nix store available in the container, allowing the container to run programs without having to re-package them into a docker image.

Arion is configured using Nix with modules, like those in NixOS. Similar to docker-compose it can therefore combine configuration from multiple files. For managing the network and containers it delegates to the docker-compose command.

Project Status

This project was born out of a process supervision need for local development environments while working on Hercules CI. (It was also born out of ancient Greek deities disguised as horses. More on that later.)

We don't use it to deploy to 'real' environments and we have no plans to do so in the future.

If you do want to use Arion for 'real' environments, you'll probably want to either build images or manage garbage collection roots if you control the deployment host. Either of these has yet to be implemented.

Install

Have Nix and Docker installed.

git clone git@github.com:hercules-ci/arion.git
nix-env -iA arion -f .

Example of usage

The command line inherits most docker-compose commands.

git clone git@github.com:nix-community/todomvc-nix.git
cd todomvc-nix/deploy/arion
arion up

"FAQ"

Do I need to use Hercules CI?

Nope, it's just Nix and Docker Compose under the hood.

Does Arion support Docker images?

Yes, you can still specify a docker image. For example:

postgres = {
  service.image = "postgres:10";
  service.volumes = [ "${toString ./.}/postgres-data:/var/lib/postgresql/data" ];
  service.environment.POSTGRES_PASSWORD = "mydefaultpass";
};

What about garbage collection?

Arion removes the need for garbage collecting docker images, delegating this task to Nix.

Arion creates a garbage collection root and cleans it up after completing the command. This means that arion up without -d is safe with respect to garbage collection. A deployment that is more serious than local development must leave a GC root on the deployment host. This use case is not supported as of now.

Why "Arion"?

Arion comes from Greek mythology. Poseidon, the god of ~~Docker~~ the seas had his eye on Demeter. Demeter tried to trick him by disguising as a horse, but Poseidon saw through the deception and they had Arion.

So Arion is a super fast divine horse; the result of some weird mixing. Also it talks.

(And we feel morally obliged to name our stuff after Greek mythology)

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