feat: Expose an app for rebuilding host configurations.

[vic]

Maybe related to #83, but this one is specific for exposing apps to build nixosConfigurations and darwinConfigurations.

My current use case is this: Expose an app that lets me apply a host configuration on a fresh OS install.

For example, suppose I have a nix-darwin system named yavanna and a fresh MacOS installation.

After installing Nix, I'd love to just run:

nix run github:vic/vix#yavanna-rebuild switch

instead of this -- a bit hairy since darwin-rebuild is not exposed as an app:

nix shell github:LnL7/nix-darwin#darwin-rebuild --command darwin-rebuild --flake github:vic/vix#yavanna switch

The same would be possible for nixosConfigurations but using nixos-rebuild.

I have already implemented it on my hosts flake

$ nix flake show
...
├───apps
│   ├───x86_64-darwin
│   │   └───yavanna-rebuild: app
│   └───x86_64-linux
│       ├───annatar-rebuild: app
│       ├───mordor-rebuild: app
│       └───nargun-rebuild: app

Now, I'm not really sure this would be something worth having in blueprint itself, since maybe my use case is very particular - or at least just a convenience for me -. So, feel free to close this issue if you think like there is no value on having something like this for many blueprint users.

[zimbatm]

This might be of the domain of the deploy tool.

Ideally we want blueprint to integrate with colmena, comin, etc... Or at least propose a generic interface those tools can use.

Potentially blueprint itself could ship with a CLI that handles these things. ie: bp host switch [--host $HOSTNAME] or nix run .#bp host switch.

All of this is kinda on the table at the moment, but I agree with the premise of the ticket, that users should have access to a blessed way to rebuild switch their host.

[vic]

Hi,

Just for reference, here's my packages/os-rebuild.nix that works as your second example CLI.

When running on an x86_64-linux, using --help will list all hosts defined for the same system. Which can be given as the first argument. Otherwise the uname -n is used to guess the current hostname.

On other systems like aarm64-darwin the script will mention darwin-rebuild instead of nixos-rebuild and will show hosts from same system.

Default action is switch meaning I just do nix run when applying new changes to my system (since I have this os-rebuild app also as default package).

$ nix run .#os-rebuild -- --help
Usage: os-rebuild [HOSTNAME] [NIXOS-REBUILD OPTIONS ...]

Default hostname: nargun
Default nixos-rebuild options: switch

Known hostnames on x86_64-linux:
annatar
mordor
nargun
nienna

Some other examples (these using nixos-rebuild options):

# with no arguments, switch the system matching current hostname.
$ nix run .#os-rebuild

# build and add to bootloader but not switch to it until reboot.
$ nix run .#os-rebuild boot

# explicit about what hostConfiguration to build an image for.
$ nix run .#os-rebuild mordor build-image

If you like this CLI utility, I could contribute it back into blueprint.