[WIP] One way to do other types of services

[copumpkin]

Motivation for this change

See #26067. Not quite sure how to expose this, and I'd be tempted to move the service modules out of the nixos folder if this catches on.

Here's how I use it:

(import ./nixos/lib/eval-config.nix {
  modules = [
    {
      services.hologram-server = {
        enable = true;
        awsAccount = "123456";
        awsDefaultRole = "foo";
        ldapBaseDN = "foobar";
        ldapBindDN = "baaz";
        ldapBindPassword = "quuux";
        ldapHost = "zomg";
      };
    }
  ];
}).config.system.build.toplevel-trivial

Then just nix-build that and you get a runner script that launches your service on any platform supported by the package.

Also, toplevel-docker will contain as many dockerTools-style containers as your config has docker-flavored services enabled.

[mention-bot]

@copumpkin, thanks for your PR! By analyzing the history of the files in this pull request, we identified @edolstra, @bjornfor and @offlinehacker to be potential reviewers.

[copumpkin]

We could probably abstract many basic simple services like this with a simple function to automatically do docker-containers, trivial-services, and maybe even systemd.services. The autogenerated config could then be merged with idiosyncratic config for any of those.

[fpletz]

I'm not sure if we should put those options into the top-level but I love the basic idea!

[Mic92]

I would keep serviceConfig.ExecStart = script; as direct commands are more transparent to the user (ex: there are visible in systemctl status). Otherwise the user has to look at the content of the script file.

[LnL7]

For my launchd modules I added command which defaults to a writeScript if a script is defined.

[copumpkin]

My main question for feedback is how do we expose this sort of thing? I was thinking of something like the following:

{
  dockerServices = config: (import ./nixos/lib/eval-config.nix {
    modules = [ config ];
  }).config.system.build.toplevel-docker;
}

But it feels a bit awkward to then stick dockerServices in all-packages.nix. I really just want to be able to call a function, pass in some service config, and get out a nice baked container image (or several). Same with trivialServices for simple shell launchers.

I imagine nix-darwin would consume it differently.

Another question is how to warn people if they decide to specify useless config in there. Someone could write networking.firewall.enable = true inside the config block they pass to dockerServices but it would just be ignored. I'd rather the user be warned not to use irrelevant config. I could do as @edolstra said in the other ticket and only selectively include modules based on some meta tag, but I liked the laziness of not doing that.

[mmahut]

What is the status of this pull request?

[mmahut]

Closing due to lack of activity, feel free re-open this if needed.