impermanence: Init module

flake.lock

@@ -192,6 +192,21 @@
         "type": "github"
       }
     },
+    "impermanence": {
+      "locked": {
+        "lastModified": 1737831083,
+        "narHash": "sha256-LJggUHbpyeDvNagTUrdhe/pRVp4pnS6wVKALS782gRI=",
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "rev": "4b3e914cdf97a5b536a889e939fb2fd2b043a170",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "impermanence",
+        "type": "github"
+      }
+    },
     "nixos-hardware": {
       "locked": {
         "lastModified": 1756750488,
@@ -280,6 +295,7 @@
         "firefox-addons": "firefox-addons",
         "flake-parts": "flake-parts",
         "home-manager": "home-manager",
+        "impermanence": "impermanence",
         "nixos-hardware": "nixos-hardware",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",

flake.nix

@@ -8,6 +8,8 @@
 
     nixos-hardware.url = "github:NixOS/nixos-hardware/master";
 
+    impermanence.url = "github:nix-community/impermanence";
+
     home-manager = {
       url = "github:nix-community/home-manager/release-25.05";
       inputs.nixpkgs.follows = "nixpkgs";
@@ -68,6 +70,7 @@
         ./flake/dev-shell.nix
         ./flake/formatter.nix
         ./flake/hosts.nix
+        ./flake/install-anywhere.nix
         ./flake/modules.nix
         ./flake/sops.nix
       ];

modules/system/impermanence.nix

@@ -0,0 +1,39 @@
+{
+  config,
+  inputs,
+  lib,
+  ...
+}:
+let
+  cfg = config.custom.impermanence;
+
+  inherit (config.custom) services;
+in
+{
+  imports = [ inputs.impermanence.nixosModules.impermanence ];
+
+  options.custom.impermanence.enable = lib.mkEnableOption "";
+
+  config = lib.mkIf cfg.enable {
+    fileSystems."/persist".neededForBoot = true;
+
+    environment.persistence."/persist" = {
+      hideMounts = true;
+
+      # See https://nixos.org/manual/nixos/stable/#ch-system-state
+      directories = [
+        "/var/lib/nixos"
+        "/var/lib/systemd"
+        "/var/log/journal"
+
+        (lib.optionalString services.tailscale.enable "/var/lib/tailscale")
+      ];
+    
+      files = [
+        "/etc/machine-id"
+        "/etc/ssh/ssh_host_ed25519_key"
+        "/etc/ssh/ssh_host_ed25519_key.pub"
+      ];
+    };
+  };
+}