Clarify Linux requirement in README (macOS seems unsupported)

[JanCVanB]

As a Nix(Ops) noob, this was particularly confusing - I assumed that since Nix supports macOS that NixOps would also support macOS. However, that does not seem to be true*. I think that adding a relevant note to the README will protect some future noobs from this confusion.

*Sources:
#260
#560
#1027
#412

[roberth]

Did you try setting up a remote builder in a VM to build for linux?
like https://github.com/nix-community/linuxkit-nix
or https://github.com/LnL7/nix-docker#running-as-a-remote-builder

I would expect deployment to cloud vms and existing machines to work. It may not be optimal (#560) or to a local vbox (#1027), but there should be no reason for it not to work altogether when deploying from a mac.

[JanCVanB]

I haven't tried those solutions, but if they are indeed the intended path for macOS users then we should add those links to the README instead. The NixOps User Guide doesn't contain any reference to "macOS" or "remote builder", and those linked repos' READMEs only mention NixOps once (in passing) between the two of them.

[roberth]

A linux builder is the best solution.

In theory there could be other options, like cross compilation or building on the target, but those are sub-optimal to say the least. Not worth pursuing.

[JanCVanB]

I tried using https://github.com/nix-community/linuxkit-nix, but the daemon wouldn't run for me on macOS 12 (Monterey). It looks like the repo is unmaintained and hasn't worked since macOS 10 (Catalina).

[JanCVanB]

I tried following the other repo's instructions here, but the daemon also wouldn't start. It looks like that repo is also unmaintained.

[JanCVanB]

If there were no maintained first-party or third-party workarounds for macOS, then would it be accurate to say that NixOps doesn't support macOS?

[roberth]

UTM is another alternative. It lets you run NixOS like you would on a physical machine. It's qemu underneath.
Plenty of other virtualization options exist too.

would it be accurate to say that NixOps doesn't support macOS?

Technically, setting up a remote builder is a distinct activity that isn't the responsibility of NixOps. There's no inherent limitation that prevents NixOps from running on macOS, so saying that it is not supported would not be accurate.
I've updated the README with some minimal info. Perhaps you could add to it with information about your own linux builder setup?
EDIT: I'd really like to guide you through it, but don't have the time now.

[roberth]

This isn't actionable now and the linux builder is more of an issue for the nix installer or nix-darwin to solve.