docs: Added docs for OVHCloud config deployment procedure

docs/gasdev.md

@@ -0,0 +1,33 @@
+# Gasdev infrastructure
+
+## Initial installation
+
+Cloud providers not always provide a NixOS install option, so I use [nixos-anywhere](https://github.com/nix-community/nixos-anywhere) for remote NixOS installation using SSH
+
+### Kexec installation
+
+As specified in [nixos-images](https://github.com/nix-community/nixos-images#kexec-tarballs):
+
+```sh
+# Run as root
+curl -L https://github.com/nix-community/nixos-images/releases/download/nixos-unstable/nixos-kexec-installer-noninteractive-x86_64-linux.tar.gz | tar -xzf- -C /root
+/root/kexec/run
+```
+
+The machine will restart in a new NixOS installation. The existing SSH keys are copied to the new installation's _root_ user.
+
+### NixOS-everywhere
+
+```sh
+nix run github:nix-community/nixos-anywhere -- --flake .#<configuration name> root@<ip address>
+```
+
+## Deploy configuration
+
+In order to deploy new configuration changes after the initial NixOS installation, I use [deploy-rs](https://github.com/serokell/deploy-rs). It requires a properly set-up **ssh-agent** and SSH keys being installed on the **gaspard** user.
+
+Then you can deploy the new configuration:
+
+```sh
+nix run github:serokell/deploy-rs .#<configuration name>
+```

hosts/OVHCloud/default.nix

@@ -23,6 +23,9 @@
       PasswordAuthentication = false;
     };
   };
+  users.users.root.openssh.authorizedKeys.keys = [
+    "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHQyRXFQ6iA5p0vDuoGSHZfajiVZPAGIyqhTziM7QgBV gaspard@nixos"
+  ];
 
   environment.systemPackages = with pkgs; [
     helix