flake.lock

@@ -33,6 +33,21 @@
         "type": "indirect"
       }
     },
+    "impermanence": {
+      "locked": {
+        "lastModified": 1694622745,
+        "narHash": "sha256-z397+eDhKx9c2qNafL1xv75lC0Q4nOaFlhaU1TINqb8=",
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "rev": "e9643d08d0d193a2e074a19d4d90c67a874d932e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "type": "github"
+      }
+    },
     "nixos-mailserver": {
       "inputs": {
         "blobs": "blobs",
@@ -123,6 +138,7 @@
     "root": {
       "inputs": {
         "flake-parts": "flake-parts",
+        "impermanence": "impermanence",
         "nixos-mailserver": "nixos-mailserver",
         "nixpkgs": "nixpkgs",
         "sops-nix": "sops-nix"

flake.nix

@@ -14,6 +14,9 @@
       url = "github:Mic92/sops-nix";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    impermanence = {
+      url = "github:nix-community/impermanence";
+    };
   };
 
   outputs = inputs@{ flake-parts, ... }:

nixos/flake-module.nix

@@ -12,6 +12,7 @@
           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

@@ -4,6 +4,7 @@ imports = [
   ./admins.nix
   ./nix_keys.nix
   (modulesPath + "/virtualisation/xen-domU.nix")
+  ../modules/impermanence.nix
   ];
 nix = {
   extraOptions = ''
@@ -27,6 +28,8 @@ users = {
   users.root.hashedPassword = "!";
 };
 
+impermanence.enable = true;
+
 sops.age.sshKeyPaths = [ "/etc/ssh/ssh_host_ed25519_key" ];
 
 environment = {