Again, nice article. I recently started using arion too and really liked it.
Did you end up running rootless podman containers? I wasn’t sure because you mentioned export DOCKER_HOST=unix:///run/podman/podman.sock as your socket path which didn’t imply rootless. I mention because I had great experience using rootless mode.
I didn’t succeed using it rootless 
I have succeeded both on Ubuntu and NixOS. Which distro and what config did you use?
Today I learned I had to use podman machine init and podman machine start 
I still need to try arion again with it, but it helped using podman-compose.
Doesn’t work for me rootless either, even with podman machine init + start.
Also, every time I do a arion up or arion down it eats up about 10GB of my /nix/store; not sure what’s causing it but it’s definitely not ideal to GC after every container change
if it uses so much things in the store, maybe you are using a pinned nixpkgs and your container require a lot of things in it? So no packages are shared with the host system and are already installed.
It seems to be an issue when using the flake integration; using a plain nix channel for arion-pkgs seems to work as expected.
I don’t use anything from the flake besides the nixpkgs that it provides (like they show in the example)