nixos/profiles: add image-based-appliance profile

nixos/modules/profiles/image-based-appliance.nix

@@ -0,0 +1,26 @@
+# This profile sets up a sytem for image based appliance usage. An appliance is
+# installed as an image, cannot be re-built, has no Nix available, and is
+# generally not meant for interactive use. Updates to such an appliance are
+# handled by updating whole partition images via a tool like systemd-sysupdate.
+
+{ lib, modulesPath, ... }:
+
+{
+
+  # Appliances are always "minimal".
+  imports = [
+    "${modulesPath}/profiles/minimal.nix"
+  ];
+
+  # The system cannot be rebuilt.
+  nix.enable = false;
+  system.switch.enable = false;
+
+  # The system is static.
+  users.mutableUsers = false;
+
+  # The system avoids interpreters as much as possible to reduce its attack
+  # surface.
+  boot.initrd.systemd.enable = lib.mkDefault true;
+  networking.useNetworkd = lib.mkDefault true;
+}