---
title: Declarative host management
---
= Declarative host management

This project uses a custom setup for declarative host management.
Specifically, it is done with a simple file at github:{github-repo}[`./setups/nixos.nix`, path=./setups/nixos.nix, rev=master] where it expects an attribute set of the hosts' metadata.
Each host in the set represents one of the hosts at github:{github-repo}[`./hosts/`, path=./hosts/, rev=master].

Each of declared hosts are then exported as part of the `images` flake output attribute where each is a derivation for building them as an image output.
For example, you can build my personalized NixOS installer ISO with the following command.

[source, shell, subs=attributes]
----
nix build {canonical-flake-url}#images.x86_64-linux.bootstrap
----

[NOTE]
====
Not every image listed here is not meant to be built as a certain output but rather deployed somewhere else.
We'll see to specify it in the following section.
====

A host metadata has a certain schema which the following example is a complete version of it.
The data is then used for certain functions in the flake definition file (i.e., `flake.nix`).

[#lst:images-metadata-example]
[source, nix]
----
{
  plover = {
    systems = [ "x86_64-linux" "aarch64-linux" ];
    format = null;
    domain = "foodogsquared.one";
    nixpkgs-channel = "nixos-unstable-small";
    home-manager-channel = "home-manager-unstable";
    modules = [
      ({ config, lib, ... }: {
        services.foo.enable = true;
      })
    ];
    deploy = {
      hostname = "plover.foodogsquared.one";
      ssh-user = "admin";
      fast-connection = true;
      auto-rollback = true;
      magic-rollback = true;
      remote-build = true;
    };
  };
}
----

For a complete reference, here are the expected attributes.

- `systems` contains a list of platforms of the host system.
This is mainly used to indicate the platform used for the nixpkgs repository.

- `format` is the image output format for the host.
It expects an accepted value from github:nix-community/nixos-generators[opts=repo] project.
To include a host as part of `nixosConfigurations`, you'll have to set this as `null`.

- `hostname` is the canonical hostname for the host.
If unset, the hostname is the name of the table key.
In the <<lst:images-metadata-example, previous example>>, if `plover.hostname` is unset, the value would be `plover` instead of `ploverrific`.

- `domain` is the domain used for networking configuration.
It is set for `networking.domain` in NixOS configuration.

- `nixpkgs-channel` is the nixpkgs channel to be used for the host.
The value could be any one of the nixpkgs flake inputs imported into this flake.
By default, it uses `nixpkgs` flake input which points to the `nixos-unstable` channel.

- `home-manager-channel` is the home-manager channel to be used for the host.
The value could be any one of the home-manager flake inputs imported into this flake.
By default, it uses `home-manager` flake input which follows the `home-manager-unstable` channel.

- `modules` is an extra list of modules to be imported with the configuration.

- `deploy` is a table containing arguments from github:serokell/deploy-rs[opts=repo].
Only a few arguments are accepted (i.e., `hostname`, `fast-connection`, `remote-build`, `magic-rollback`, and `auto-rollback`).
Once this attribute is present, it will be included as part of `nixosConfigurations` flake output no matter what `format` is given.

Those imported NixOS configurations are also exported as part of the deploy nodes for deploy-rs with the `nixos` prefix.
For example, here's the command to deploy my Plover server.

[source, shell, subs=attributes]
----
deploy {canonical-flake-url}#nixos-plover
----