first impermanence config

nixos/flake-module.nix

@@ -21,6 +21,7 @@
           imports = [
             (import (./. + "/machines/${name}/configuration.nix") inputs)
             inputs.sops-nix.nixosModules.sops
+            inputs.impermanence.nixosModules.impermanence
           ];
         };
     in lib.genAttrs machines makeSystem);

nixos/modules/impermanence.nix

@@ -0,0 +1,42 @@
+{lib, config, ...} :
+
+let 
+  inherit (lib)
+    mkEnableOption
+    mkIf
+    mkOption
+    types
+    ;
+  cfg = config.impermanence;
+in
+
+{
+imports = [ ];
+
+options.impermanence = {
+  enable = mkEnableOption "impermanence";
+  storagePath = mkOption {
+    type = types.path;
+    default = "/persist/persist";
+    description = "The path where persistent data is stored";
+  };
+  name = mkOption {
+    type = types.str;
+    default = "persist";
+    description = "the name of the persistent data store";
+  };
+};
+
+config = mkIf cfg.enable {
+  environment.persistence.${cfg.name} = {
+    persistentStoragePath = cfg.storagePath;
+    directories = [
+      "/var/log"
+      "/etc/ssh"
+      "/var/lib/nixos"
+    ];
+  };
+  environment.etc.machine-id.source = "${cfg.storagePath}/machine-id";
+};
+
+}

nixos/roles/default.nix

@@ -3,6 +3,7 @@
 imports = [
   ./admins.nix
   ./nix_keys.nix
+  ../modules/impermanence.nix
   ];
 nix = {
   extraOptions = ''
@@ -25,6 +26,8 @@ users = {
   mutableUsers = false;
 };
 
+impermanence.enable = true;
+
 sops.age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
 
 environment = {