refactored xen_guest.nix

README.md

@@ -1,13 +1,111 @@
 # nixConfig
 
 ## Build a machine
-### Local
+There are multiple ways to build and deploy a machine configuration. Which is the
-If you want to build the machineconfiguration for machine <name>
+most appropriate depends on the context and scenario. So first there will be a general
-run
+explanation how this works and afterwards we will talk about some scenarios.
+
+If you run `nix flake show` you should get an output similiar to this
 ```
-nix build .#nixosConfiguration.<name>.config.system.build.toplevel
+$ nix flake show
+git+file:///home/nerf/git/nixConfig?ref=refs%2fheads%2fnyarlathtop&rev=9d0eb749287d1e9e793811759dfa29469ab706dc
+├───apps
+│   └───x86_64-linux
+├───checks
+│   └───x86_64-linux
+├───devShells
+│   └───x86_64-linux
+├───formatter
+├───legacyPackages
+│   └───x86_64-linux omitted (use '--legacy' to show)
+├───nixosConfigurations
+│   └───nyarlathotep: NixOS configuration
+├───nixosModules
+├───overlays
+└───packages
+    └───x86_64-linux
+```
+we can see there is an output callled `nixosConfigurations.nyarlathotep`. Which contains the config of the machine
+called nyarlathotep. `nixosConfigurations` is special in that sense, that `nixos-rebuild` will automatically look
+for this key and assume how it is structured. The interesting part for us is the derivation `config.system.build.toplevel`.
+Its closure contains the whole system and the resulting derivation a script that changes the current system to
+that derivation. (called `/bin/switch-to-configuration`).
+
+So what we want to archive is populate the nix store of the target machine with the closure of the derivation
+`.#nixosConfigurations.<name>.config.system.build.toplevel` and run the the resulting script on the target machine.
+
+
+### Local
+It has multiple benefits to build the system config on the local computer and push it to the target server.
+For example one doesn't stress the server with the load coming with evaluating the expression. Also the server
+doesn't need to fetch the build dependencies this way. One has a local check if at least the nix syntax was correct.
+And so on...
+
+#### Build
+If you have this repository local in your current directory you can just run:
+```
+$ nix build .#nixosConfigurations.<name>.config.system.build.toplevel
 ```
 
+But you don't need to clone this repository for more on flake urls see the `nix flake --help` documentation.
+
+#### Copy
+After we build the derivation we need to get the closure onto the target system. Luckily nix has tools to do that
+via ssh. We could just run:
+```
+$ nix copy -s --to <however you setup your ssh stuff> .#nixosConfigurations.<name>.config.system.build.toplevel
+```
+we do not need the flake anymore, instead of specifying the derivation name we could also give the store path
+directly.
+
+The `-s` is important it makes the target machine substitute all derivations it can (by default from chache.nixos.org).
+So you only upload config files and self build things.
+
+To be able to copy things to a machine they need to be signed by someone trusted. Additional trusted nix keys are handled
+in `./nixos/roles/nix_keys.nix`. So to get yourself trusted you either need to install one derivation from the machine itself,
+or find someone who is already trusted.
+
+For more information on signing and key creation see `nix store sign --help` and `nix key --help`.
+
+#### Activate
+Log into the remote machine and execute
+```
+# /nix/store/<storepath>/bin/switch-to-configuration boot
+```
+That will setup a configuration switch at reboot. You can also switch the configuration live. For more
+details consider the `--help` output of that script.
+
+
+If you have a `nixos-rebuild` available on your system it can automatize these things with the `--flake` and
+`--target-host` parameters. But there are some pitfalls so look at the `nixos-rebuild` documentation beforehand.
+
 ### On the machine
-clone this repo to `/etc/nixos/` and `nixos-rebuild` that will select
+clone this repo to `/etc/nixos/` and `nixos-rebuild boot` or `nixos-rebuild switch` that will select
-the appropriate machine based on hostname
+the appropriate machine based on hostname.
+
+If the hostname is not correct, or you don't want to clone this flake you can also use the `--flake` parameter.
+
+In any case, to switch the system configuration you will need to have root priviledges on the target machine.
+
+
+## How this flake is organized
+
+This flake uses `flake-parts` see [flake.parts](https://flake.parts) for more details. It makes handling
+`system` and some other moudles related things more convenient.
+For the general layout of nixos system config and modules, please see the corresponding documentation.
+
+The toplevel `flake.nix` contains the flake inputs as usual and only calls a file `flake-module.nix`
+this toplevel `flake-module.nix` imports further more specialiesed `flake-modules.nix` files from subdirectories.
+Right now the only one is `nixos/flake-module.nix`.
+
+the `nixos` folder contains all machine configurations. It sepreates in two folders `nixos/machines` and `nixos/roles`.
+
+`nixos/machines` contains all machine specific configuration (in a subfolder per machine). Like hardware configuration, specific
+network configuration. And service configuration that are too closely intervowen with the rest of that machine. It also
+contains the root config for that machine called `configuration.nix`. This file usually only includes other modules.
+
+`nixos/roles` contains config that is pontentially shared by some machines. It is expected that `nixos/roles/default.nix`
+is imported as (`../../roles`) in every machine. Notable are the files `nixos/roles/admins.nix` which contains
+common admin accounts for these machines and `nixos/roles/nix_keys.nix` which contains the additional trusted
+keys for the nix store.
+

nixos/machines/nyarlathotep/boot.nix

@@ -1,8 +0,0 @@
-{
-  imports = [ ];
-  boot.loader.grub = {
-    device = "nodev";
-    enable = true;
-  };
-}
-

nixos/machines/nyarlathotep/configuration.nix

@@ -5,7 +5,7 @@ imports = [
   ./hardware-configuration.nix
   (import ./mail.nix flake-inputs)
   ../../roles
-  ./boot.nix
+  ../../roles/xen_guest.nix
   ./network.nix
 ];
 

nixos/machines/nyarlathotep/hardware-configuration.nix

@@ -1,11 +1,6 @@
 {config, lib, pkgs, modulesPath, ...}: {
   imports = [ ];
 
-  boot.initrd.availableKernelModules =
-    [ "ata_piix" "sr_mod" "xen_blkfront" ];
-  boot.kernelModules = [ ];
-  boot.extraModulePackages = [ ];
-
   fileSystems."/" = {
     device = "/dev/disk/by-uuid/a72da670-f631-49b1-bcb3-6d378cc1f2d0";
     fsType = "ext4";

nixos/roles/xen_guest.nix

@@ -0,0 +1,15 @@
+{...}: {
+  imports = [ ];
+  boot = {
+    loader.grub = {
+      device = "nodev";
+      enable = true;
+    };
+    initrd = {
+      availableKernelModules = [ "ata_piix" "sr_mod" "xen_blkfront" ];
+      kernelModules = [ ];
+    };
+    extraModulePackages = [ ];
+  };
+}
+