module does not build:

$ nix build .#nixosConfigurations.vm.config.system.build.vm
    error:
	   … while calling the 'derivationStrict' builtin

	     at /builtin/derivation.nix:9:12: (source not available)

	   … while evaluating derivation 'nixos-vm'
	     whose name attribute is located at /nix/store/ikx99aci297hpgys7114fjwyf38iv9qi-source/pkgs/stdenv/generic/make-derivation.nix:348:7

	   … while evaluating attribute 'buildCommand' of derivation 'nixos-vm'

	     at /nix/store/ikx99aci297hpgys7114fjwyf38iv9qi-source/pkgs/build-support/trivial-builders/default.nix:87:14:

	       86|       enableParallelBuilding = true;
	       87|       inherit buildCommand name;
		 |              ^
	       88|       passAsFile = [ "buildCommand" ]

	   (stack trace truncated; use '--show-trace' to show the full trace)

	   error: attribute 'system' missing

	   at /nix/store/ikx99aci297hpgys7114fjwyf38iv9qi-source/lib/modules.nix:506:28:

	      505|         builtins.addErrorContext (context name)
	      506|           (args.${name} or config._module.args.${name})
		 |                            ^
	      507|       ) (lib.functionArgs f);

flake.nix

@@ -36,53 +36,19 @@
     ...
   }:
     flake-utils.lib.eachDefaultSystem (system: let
-      pkgs = import nixpkgs {
+      pkgs = import ./pkgs.nix {
-        inherit system;
+        inherit nixpkgs system geoip2-tarball;
-        overlays = [
-          (_: super: {
-            python3 = super.python3.override {
-              packageOverrides = _: python-super: {
-                django = python-super.django_5;
-              };
-            };
-            geoip-mmdb = pkgs.callPackage ./pkgs/geoip-mmdb.nix {
-              inherit geoip2-tarball;
-            };
-            e11sync-static = pkgs.callPackage ./pkgs/e11sync-static.nix {};
-            e11sync-frontend = pkgs.callPackage ./pkgs/e11sync-frontend.nix {};
-            e11sync-backend = pkgs.callPackage ./pkgs/e11sync-backend.nix {};
-          })
-        ];
-      };
-
-      geoip-mmdb = pkgs.callPackage ./pkgs/geoip-mmdb.nix {
-        inherit geoip2-tarball;
-      };
-
-      e11sync-static = pkgs.callPackage ./pkgs/e11sync-static.nix {};
-
-      e11sync-frontend = pkgs.callPackage ./pkgs/e11sync-frontend.nix {
-        inherit e11sync-static;
-      };
-
-      e11sync-backend = pkgs.callPackage ./pkgs/e11sync-backend.nix {
-        inherit geoip-mmdb;
-        e11sync-static-manifest = e11sync-static.passthru.manifest;
-      };
-
-      e11sync-module = import ./modules/e11sync {
-        inherit e11sync-backend e11sync-frontend;
       };
     in {
       packages = {
-        inherit geoip-mmdb;
+        inherit (pkgs) geoip-mmdb;
-        inherit e11sync-static;
+        inherit (pkgs) e11sync-static;
-        inherit e11sync-frontend;
+        inherit (pkgs) e11sync-frontend;
-        inherit e11sync-backend;
+        inherit (pkgs) e11sync-backend;
       };
 
       checks = {
-        e11sync-unit = e11sync-backend.passthru.tests.unit;
+        e11sync-unit = pkgs.e11sync-backend.passthru.tests.unit;
         pre-commit-check = pre-commit-hooks.lib.${system}.run {
           src = ./.;
           hooks = {
@@ -98,9 +64,6 @@
         '';
       };
 
-      nixosModules.e11sync = e11sync-module;
-      nixosModules.default = e11sync-module;
-
       apps = {
         e11sync-frontend = {
           type = "app";
@@ -115,7 +78,7 @@
                   debug
                 }
                 :8001
-                ${builtins.readFile "${e11sync-frontend}"}
+                ${builtins.readFile "${pkgs.e11sync-frontend}"}
               '';
             }} --adapter caddyfile'');
         };
@@ -124,7 +87,7 @@
           name = "e11sync-backend";
           program = toString (pkgs.writeShellScript "wrapper" ''
             export E11SYNC_DATABASE_PATH=$PWD/db.sqlite3
-            exec ${e11sync-backend}/bin/e11sync-backend
+            exec ${pkgs.e11sync-backend}/bin/e11sync-backend
           '');
         };
       };
@@ -145,7 +108,7 @@
           libmaxminddb
           dart-sass
         ];
-        GEOIP_PATH = "${geoip-mmdb}";
+        GEOIP_PATH = "${pkgs.geoip-mmdb}";
         E11SYNC_DEBUG = "1";
         LOCALE_ARCHIVE = "${pkgs.glibcLocales}/lib/locale/locale-archive";
         inherit (self.checks.${system}.pre-commit-check) shellHook;
@@ -162,6 +125,6 @@
           self.nixosModules.e11sync
         ];
       };
-      nixosModules.e11sync = import ./modules/e11sync geoip2-tarball;
+      nixosModules.e11sync = import ./modules/e11sync nixpkgs;
     };
 }

modules/e11sync/default.nix

@@ -1,9 +1,12 @@
-geoip2-tarball: {
+nixpkgs: {
   config,
   lib,
-  pkgs,
+  system,
+  geoip2-tarball,
   ...
-}: {
+}: let
+  pkgs = import ../../pkgs.nix {inherit nixpkgs system geoip2-tarball;};
+in {
   options.e11sync = with lib.types; {
     enable = lib.mkEnableOption "Enable e11sync";
     secretKeyPath = lib.mkOption {type = oneOf [path (enum ["unsafe"])];};
@@ -28,21 +31,10 @@ geoip2-tarball: {
 
   config = let
     cfg = config.e11sync;
-    geoip-mmdb = pkgs.callPackage ../../pkgs/geoip-mmdb.nix {
-      inherit geoip2-tarball;
-    };
-    e11sync-static = pkgs.callPackage ../../pkgs/e11sync-static.nix {};
-    e11sync-frontend = pkgs.callPackage ../../pkgs/e11sync-frontend.nix {
-      inherit e11sync-static;
-    };
-    e11sync-backend = pkgs.callPackage ../../pkgs/e11sync-backend.nix {
-      inherit e11sync-static geoip-mmdb;
-      inherit (cfg) backendPort databasePath;
-    };
   in
     lib.mkIf cfg.enable {
       environment.systemPackages = [
-        e11sync-backend
+        pkgs.e11sync-backend
       ];
 
       systemd.services = {
@@ -67,7 +59,7 @@ geoip2-tarball: {
               StateDirectory = "e11sync-backend";
               WorkingDirectory = "/var/lib/e11sync-backend";
               KillSignal = "SIGQUIT";
-              ExecStart = "${e11sync-backend}/bin/e11sync-backend";
+              ExecStart = "${pkgs.e11sync-backend}/bin/e11sync-backend";
 
               MemoryHigh = "1535M";
               MemoryMax = "4096M";
@@ -79,7 +71,7 @@ geoip2-tarball: {
               ProtectControlGroups = true;
             }
             (lib.mkIf cfg.migrateOnStart {
-              ExecStartPre = "${e11sync-backend}/bin/e11sync migrate";
+              ExecStartPre = "${pkgs.e11sync-backend}/bin/e11sync migrate";
             })
             (lib.mkIf (cfg.secretKeyPath != "unsafe") {
               LoadCredential = "secret_key:${cfg.secretKeyPath}";
@@ -89,6 +81,6 @@ geoip2-tarball: {
       };
 
       services.caddy.virtualHosts."${cfg.vhost}".extraConfig =
-        builtins.readFile "${e11sync-frontend}";
+        builtins.readFile "${pkgs.e11sync-frontend}";
     };
 }

pkgs.nix

@@ -0,0 +1,25 @@
+{
+  nixpkgs,
+  system,
+  geoip2-tarball,
+}: let
+  inherit (import nixpkgs {inherit system;}) callPackage;
+in
+  import nixpkgs {
+    inherit system;
+    overlays = [
+      (_: super: {
+        python3 = super.python3.override {
+          packageOverrides = _: python-super: {
+            django = python-super.django_5;
+          };
+        };
+        geoip-mmdb = callPackage ./pkgs/geoip-mmdb.nix {
+          inherit geoip2-tarball;
+        };
+        e11sync-static = callPackage ./pkgs/e11sync-static.nix {};
+        e11sync-frontend = callPackage ./pkgs/e11sync-frontend.nix {};
+        e11sync-backend = callPackage ./pkgs/e11sync-backend.nix {};
+      })
+    ];
+  }