refactor(llama-router): extract atlas llm setup into reusable module

Assisted-by: pi (opus-4.8)

hosts/atlas/llm-server.nix

@@ -1,9 +1,4 @@
-{
-  lib,
-  outputs,
-  pkgs,
-  ...
-}: let
+{outputs, ...}: let
   port = 18080;
   models = {
     # flash-attn + q8_0 KV cache halves the KV footprint to stay under 8GB VRAM.
@@ -42,6 +37,11 @@
     };
   };
 in {
+  services.llama-router = {
+    enable = true;
+    inherit port models;
+  };
+
   services.nginx.virtualHosts."llm.m7.rs" = {
     locations."/" = {
       proxyPass = "http://localhost:${toString port}";
@@ -54,44 +54,4 @@ in {
       '';
     };
   };
-
-  users.users.llama = {
-    isSystemUser = true;
-    group = "llama";
-    home = "/var/lib/llama";
-  };
-  users.groups.llama = {};
-
-  systemd.services.llama-cpp-router = {
-    description = "Local llama.cpp router API";
-    after = ["network-online.target"];
-    wants = ["network-online.target"];
-    wantedBy = ["multi-user.target"];
-    environment = {
-      XDG_CACHE_HOME = "/var/lib/llama";
-      XDG_DATA_HOME = "/var/lib/llama";
-    };
-    path = [pkgs.llama-cpp-vulkan];
-    script = lib.concatStringsSep " " [
-      "llama-server"
-      # No --models-dir: all models come from --models-preset below.
-      # The preset parser reads INI values verbatim (no quote stripping), so use
-      # plain INI, not TOML - quoted strings would keep their literal quotes.
-      "--models-preset ${(pkgs.formats.ini {}).generate "llama-cpp-models.ini" models}"
-      "--models-max 1"
-      "--host 127.0.0.1"
-      "--port ${toString port}"
-    ];
-    serviceConfig = {
-      User = "llama";
-      Group = "llama";
-      StateDirectory = "llama";
-      RuntimeDirectory = "llama";
-      SupplementaryGroups = ["render" "video"];
-      Restart = "on-failure";
-      RestartSec = 2;
-      # llama-server can dawdle on shutdown; SIGKILL it after 15s.
-      TimeoutStopSec = 15;
-    };
-  };
 }

modules/nixos/default.nix

@@ -4,4 +4,5 @@
   opencode = import ./opencode.nix;
   openrgb = import ./openrgb.nix;
   nix-registry-prometheus-exporter = import ./nix-registry-prometheus-exporter.nix;
+  llama-router = import ./llama-router.nix;
 }

modules/nixos/llama-router.nix

@@ -0,0 +1,91 @@
+{
+  pkgs,
+  lib,
+  config,
+  ...
+}: let
+  cfg = config.services.llama-router;
+in {
+  options.services.llama-router = {
+    enable = lib.mkEnableOption "the local llama.cpp router API";
+
+    package = lib.mkPackageOption pkgs "llama-cpp-vulkan" {};
+
+    models = lib.mkOption {
+      type = (pkgs.formats.ini {}).type;
+      default = {};
+      description = ''
+        Model presets to serve, as an attrset mapping each model name to its
+        llama-server settings (e.g. `hf`, `ctx-size`, `n-gpu-layers`).
+      '';
+    };
+
+    host = lib.mkOption {
+      type = lib.types.str;
+      default = "127.0.0.1";
+      description = "Address llama-server binds to.";
+    };
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 18080;
+      description = "Port llama-server listens on.";
+    };
+
+    user = lib.mkOption {
+      type = lib.types.str;
+      default = "llama";
+      description = "User to run the router service as.";
+    };
+
+    group = lib.mkOption {
+      type = lib.types.str;
+      default = "llama";
+      description = "Group to run the router service as.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    users.users = lib.mkIf (cfg.user == "llama") {
+      llama = {
+        isSystemUser = true;
+        group = cfg.group;
+        home = "/var/lib/llama";
+      };
+    };
+    users.groups = lib.mkIf (cfg.group == "llama") {
+      llama = {};
+    };
+
+    systemd.services.llama-cpp-router = {
+      description = "Local llama.cpp router API";
+      after = ["network-online.target"];
+      wants = ["network-online.target"];
+      wantedBy = ["multi-user.target"];
+      environment = {
+        XDG_CACHE_HOME = "/var/lib/llama";
+        XDG_DATA_HOME = "/var/lib/llama";
+      };
+      path = [cfg.package];
+      script = lib.concatStringsSep " " [
+        "llama-server"
+        # No --models-dir: all models come from --models-preset below.
+        "--models-preset ${(pkgs.formats.ini {}).generate "llama-cpp-models.ini" cfg.models}"
+        "--models-max 1"
+        "--host ${cfg.host}"
+        "--port ${toString cfg.port}"
+      ];
+      serviceConfig = {
+        User = cfg.user;
+        Group = cfg.group;
+        StateDirectory = "llama";
+        RuntimeDirectory = "llama";
+        SupplementaryGroups = ["render" "video"];
+        Restart = "on-failure";
+        RestartSec = 2;
+        # llama-server can dawdle on shutdown; SIGKILL it after 15s.
+        TimeoutStopSec = 15;
+      };
+    };
+  };
+}