An introduction to Arion: learn why we built it on top of Docker Compose, how it integrates with Nix and how you can use it. As Arion is mostly an application of the Nix modules system, we share our experience of building it. Arion is a tool that integrates Nix and NixOS into Docker Compose. - introduction to Docker Compose and Arion - how to write a deployment - how Arion uses the Nix module system to its advantage - what's next for Arion Arion started out as a little bash script with the goal of doing process management for our local development setups internally for Hercules CI, on top of Docker Compose. It has since grown to become an independent tool with support for NixOS in Docker, a significant subset of docker-compose.yaml and support for building actual images. Arion is written with the Nix module system, which means that deployments are as powerful as Arion's internals and that you can build your own abstractions into your deployments. It also means that the format of its logic may be familiar and it's easy to contribute.