Buck is an opensource build system. At Facebook, we’ve taught it to build container images that work with systemd. At Facebook we use an open-source build system called Buck. Buck is a build system designed to provide more strong guarantees of incremental builds, reproducibility, and dependency management. Open-source Buck can now be used to construct fully described and fully self-contained container images that work with systemd! I will show how we use this tool internally at Facebook and how it can be used externally (It’s open-source!) to build service containers for use by systemd. I will dive into the the details of how these builds are performed with systemd-nspawn, how we use the Buck system to define the systemd services and their dependencies, and how these images work at runtime.