That's correct. I recently ended up using `buildLayerImage` (actually `buildLayerImageWithNixDb`) for CI, not only to run a single process, but also `systemd` and multiple processes. `podman` comes with built-in support for `systemd`.
Yum is "as dead" as one might think Fedora 22 is "production ready!" The reality is RHEL 6, RHEL 7 and many other distributions use Yum and they are not going to go away anytime soon.
[Here](https://github.com/fdb-rs/fdb/blob/fdb-0.2.2/nix/ci/flake.ni...) is relevant code.