feat: add hetzner storage box intergation for restic

README.md

@@ -18,6 +18,7 @@ EFI/BIOS boot config | Module | [Link](./modules/boot.nix) | - | - | Allows you
 Nginx recommended options | Module | [Link](./modules/nginx.nix) | - | agenix | Sets many recommended settings for nginx with a single switch plus some opinionated defaults. Also adds a switch for setting recommended security headers on each location.
 Node options | Module | [Link](./modules/node.nix) | - | - | A module that stores meta information about your nodes (hosts). Required for some other modules that operate across nodes.
 Guests (MicroVMs & Containers) | Module | [Link](./modules/guests) | zfs, node options | - | This module implements a common interface to use guest systems with microvms or nixos-containers.
+Restic hetzner storage box setup | Module | [Link](./modules/restic.nix) | - | - | This module exposes new options for restic backups that allow a simple setup of hetzner storage boxes. There's [an app](./apps/setup-hetzner-storage-boxes.nix) that you should expose on your flake to automate remote setup.
 
 #### Home Manager Modules
 

apps/setup-hetzner-storage-boxes.nix

@@ -0,0 +1,100 @@
+{
+  pkgs,
+  nixosConfigurations,
+  decryptIdentity,
+}: let
+  inherit
+    (pkgs.lib)
+    attrValues
+    concatLines
+    concatStringsSep
+    escapeShellArg
+    filterAttrs
+    flatten
+    flip
+    getExe
+    groupBy
+    head
+    length
+    mapAttrs
+    mapAttrsToList
+    optional
+    throwIf
+    unique
+    ;
+
+  allBoxDefinitions = flatten (
+    flip map (attrValues nixosConfigurations) (
+      hostCfg:
+        flip map (attrValues hostCfg.config.services.restic.backups) (
+          backupCfg:
+            optional backupCfg.hetznerStorageBox.enable backupCfg.hetznerStorageBox
+        )
+    )
+  );
+
+  subUserFor = box: "${box.mainUser}-sub${toString box.subUid}";
+  boxesBySubuser = groupBy subUserFor allBoxDefinitions;
+
+  # We need to know the main storage box user to create subusers
+  boxSubuserToMainUser =
+    flip mapAttrs boxesBySubuser (_: boxes:
+      head (unique (flip map boxes (box: box.mainUser))));
+
+  boxSubuserToPrivateKeys =
+    flip mapAttrs boxesBySubuser (_: boxes:
+      unique (flip map boxes (box: box.sshPrivateKeyFile)));
+
+  # Any subuid that has more than one path in use
+  boxSubuserToPaths =
+    flip mapAttrs boxesBySubuser (_: boxes:
+      unique (flip map boxes (box: box.path)));
+
+  duplicates = filterAttrs (_: boxes: length boxes > 1) boxSubuserToPaths;
+
+  # Only one path must remain per subuser.
+  boxSubuserToPath = throwIf (duplicates != {}) ''
+    At least one storage box subuser has multiple paths assigned to it:
+    ${concatStringsSep "\n" (mapAttrsToList (n: v: "${n}: ${toString v}") duplicates)}
+  '' (mapAttrs (_: head) boxSubuserToPaths);
+
+  appendPubkey = privateKey: ''
+    PATH="$PATH:${pkgs.age-plugin-yubikey}/bin" ${pkgs.rage}/bin/rage -d -i ${decryptIdentity} ${escapeShellArg privateKey} \
+      | (exec 3<&0; ssh-keygen -f /proc/self/fd/3 -y) \
+      >> "$TMPFILE"
+  '';
+
+  setupSubuser = subuser: privateKeys: let
+    mainUser = boxSubuserToMainUser.${subuser};
+    path = boxSubuserToPath.${subuser};
+  in ''
+    echo "${mainUser} (for ${subuser}): Removing old ${path}/.ssh if it exists"
+    # Remove any .ssh folder if it exists
+    ${pkgs.openssh}/bin/ssh -p 23 "${mainUser}@${mainUser}.your-storagebox.de" -- rm -r ./${path}/.ssh &>/dev/null || true
+    echo "${mainUser} (for ${subuser}): Creating ${path}/.ssh"
+    # Create subuser directory and .ssh
+    ${pkgs.openssh}/bin/ssh -p 23 "${mainUser}@${mainUser}.your-storagebox.de" -- mkdir -p ./${path}/.ssh
+
+    # Derive and upload all authorized keys
+    TMPFILE=$(mktemp)
+    ${concatLines (map appendPubkey privateKeys)}
+    echo "${mainUser} (for ${subuser}): Uploading $(wc -l < "$TMPFILE") authorized_keys"
+    ${pkgs.openssh}/bin/scp -P 23 "$TMPFILE" "${mainUser}@${mainUser}.your-storagebox.de":./${path}/.ssh/authorized_keys
+    rm "$TMPFILE"
+  '';
+in {
+  type = "app";
+  program = getExe (pkgs.writeShellApplication {
+    name = "setup-hetzner-storage-boxes";
+    text = ''
+      set -euo pipefail
+
+      ${concatLines (mapAttrsToList setupSubuser boxSubuserToPrivateKeys)}
+
+      echo
+      echo "Please visit https://robot.hetzner.com/storage and make sure"
+      echo "that the following subusers are setup correctly:"
+      ${concatLines (mapAttrsToList (u: p: "echo '  ${u}: ${p}'") boxSubuserToPath)}
+    '';
+  });
+}

modules/default.nix

@@ -7,6 +7,7 @@
     ./interface-naming.nix
     ./nginx.nix
     ./node.nix
+    ./restic.nix
   ];
 
   nixpkgs.overlays = [

modules/restic.nix

@@ -0,0 +1,56 @@
+{lib, ...}: let
+  inherit
+    (lib)
+    mkEnableOption
+    mkIf
+    mkOption
+    types
+    ;
+in {
+  options.services.restic.backups = mkOption {
+    type = types.attrsOf (types.submodule ({config, ...}: {
+      options.hetznerStorageBox = {
+        enable = mkEnableOption "Automatically configure this backup to use the given hetzner storage box. Will use SFTP via SSH.";
+
+        mainUser = mkOption {
+          type = types.str;
+          description = ''
+            The main user. While not technically required for restic, we still use it to
+            derive the subuser name and it is required for the automatic setup script
+            that creates the users.
+          '';
+        };
+
+        subUid = mkOption {
+          type = types.int;
+          description = "The id of the subuser that was allocated on the hetzner server for this backup.";
+        };
+
+        path = mkOption {
+          type = types.str;
+          description = ''
+            The remote path to backup into. While not technically required for restic
+            (since the subuser is chrooted on the remote), it is required for the
+            automatic setup script that creates the users.
+          '';
+        };
+
+        sshPrivateKeyFile = mkOption {
+          type = types.path;
+          description = "The path to the ssh private key to use for uploading backups. Don't use a path from the nix store!";
+        };
+      };
+
+      config = let
+        subuser = "${config.hetznerStorageBox.mainUser}-sub${toString config.hetznerStorageBox.subUid}";
+        url = "${subuser}@${subuser}.your-storagebox.de";
+      in
+        mkIf config.hetznerStorageBox.enable {
+          repository = "sftp://${url}:23/";
+          extraOptions = [
+            "sftp.command='ssh -s sftp -p 23 -i ${config.hetznerStorageBox.sshPrivateKeyFile} ${url}'"
+          ];
+        };
+    }));
+  };
+}