[viraptor]

> don’t want to rebuild my system to update an app.

You don't have to do that - there's lots of other options. (Although the system shouldn't rebuild if you don't update your channels, so the premise is interesting/suspicious.)

You can build your app independently against a pinned nixpkgs version. You can build the app and export/import that closure on another system. You can build the app itself using nix-build without engaging the nixos switch.

[ratorx]

Building the app is not the problem, Nix adds minimal overhead for that. Deploying the app is annoying because changing a systemd service requires a nixos-rebuild, which is pretty slow on a Raspberry Pi.

There’s no good way to have an auto-updating non-NixOS systemd service on NixOS, because it’s not designed to co-exist with other things.

Also, NixOS is pretty much a DSL around systemd for this kind of thing. Systemd is already fairly declarative, so the indirection seems a bit unnecessary.