Having a good CI is a must-have for any serious software project nowadays.

Modern CI platforms and tools make it trivial to build an initial CI configuration and have it plugged in the development workflow. They however don't solve the ongoing maintenance cost, as any CI system requires maintaining a specific logic for creating a suitable build environment on the CI runners, meaning that every change to the build requirements will have to be duplicated in the CI setup. And that duplication means that the different setups will inevitably drift out of sync, leading to head-banging errors that will only happen in one setup but not another.

This talk is about leveraging Nix to be able to declare an environment that can be used both locally, and on any CI service, so that the maintenance cost becomes minimal, and the environments are guaranteed to stay in sync.