libvirt: Allow control over boot image configuration

[Nadrieril]

This PR adds a deployment.libvirtd.boot_config option that is used to specify the NixOS configuration to use for the first boot.
This is useful in non-standard configurations, for example in networks without DHCP, in case of needing external filesystems, or if special devices are enabled.
It ensures sharing of the base image to make build times reasonable.

[rbvermaa]

Could you remove the 499 fix from this PR?

[Nadrieril]

It doesn't work without it, so I would rather wait for #596 to be merged before removing it (by then rebasing on top of master).

[domenkozar]

I don't think we should inline make-disk-image here. The last thing we want is to fragment that code again, after investing so much time to generalize it.

[Nadrieril]

Well, it was already pretty much inlined already. Should I replace it with make-disk-image directly ? I thought there were some issues with it like NixOS/nixpkgs#20471.
On the other hand I do need to inline bits of it for the edit_image function, because I don't think there exists any equivalent function in nixpkgs yet.

[copumpkin]

Also somewhat relevant (especially if you duplicate the image building code): NixOS/nixpkgs#21943

[Nadrieril]

Yes, I'm following your PRs closely :)

[3noch]

#596 was merged!

[Nadrieril]

I'm closing this because I'm not using nixops anymore. If anyone still wants this, you can fetch the branch from my fork and make a new PR yourself.

[3noch]

@Nadrieril Would you mind leaving it open? Regardless of whether or not it is useful to you, it is likely still useful to the rest of us.

[domenkozar]

+1, also if you can let us know why you're not using nixops, it might be useful feedback :)

[Nadrieril]

Ok.
I'm not using nixops anymore for two reasons: I needed something like nixos-rebuild test and after trying to implement it in nixops I gave up; also I wanted to have a build host separate from the targethost.
In the end it turned out that nixos-rebuild did almost everything I needed. I'm only missing libvirt management but I'm working on a nixos libvirt module that would do that.

[Nadrieril]

Oh, and also I wanted remote deployment but the PR to add remote libvirt deployment seems stalled. And statelessness as much as possible, to make it easier to deploy from multiple machines.
Sorry if I sound like I'm complaining, I think the general idea is that nixops was not the tool I needed.

[grahamc]

Hello!

Thank you for this PR.

In the past several months, some major changes have taken place in
NixOps:

1. Backends have been removed, preferring a plugin-based architecture.
   Here are some of them:

   • https://github.com/NixOS/nixops-aws
   • https://github.com/NixOS/nixops-hetzner
   • https://github.com/nix-community/nixops-vbox
   • https://github.com/nix-community/nixops-libvirtd
   • https://github.com/nix-community/nixops-datadog

2. NixOps Core has been updated to be Python 3 only, and at the
   same time, MyPy type hints have been added and are now strictly
   required during CI.

This is all accumulating in to what I hope will be a NixOps 2.0
release. There is a tracking issue for that:
#1242 . It is possible that
more core changes will be made to NixOps for this release, with a
focus on simplifying NixOps core and making it easier to use and work
on.

My hope is that by adding types and more thorough automated testing,
it will be easier for contributors to make improvements, and for
contributions like this one to merge in the future.

However, because of the major changes, it has become likely that this
PR cannot merge right now as it is. The backlog of now-unmergable PRs
makes it hard to see which ones are being kept up to date.

If you would like to see this merge, please bring it up to date with
master and reopen it. If the or mypy type checking fails, please
correct any issues and then reopen it. I will be looking primarily at
open PRs whose tests are all green.

Thank you again for the work you've done here, I am sorry to be
closing it now.

Graham