feat(nixos): run Valheim in a guest

configs/nixos/guests/valheim.nix

@@ -0,0 +1,104 @@
+{
+  config,
+  lib,
+  ...
+}:
+let
+  cfg = config.guests.valheim;
+  steamDir = "/data/steamcmd";
+  installDir = "/data/server";
+  stateDir = "/data/state";
+in
+{
+  options.guests.valheim = {
+    steamPath = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "/srv/steamcmd";
+      description = "Host path bind-mounted as SteamCMD's metadata directory.";
+    };
+
+    installPath = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "/srv/valheim/server";
+      description = "Host path bind-mounted as Valheim's server install directory.";
+    };
+
+    statePath = lib.mkOption {
+      type = lib.types.nullOr lib.types.str;
+      default = null;
+      example = "/srv/valheim/state";
+      description = "Host path bind-mounted as Valheim's world state directory.";
+    };
+
+    serverName = lib.mkOption {
+      type = lib.types.str;
+      default = "valheim";
+      description = "Name shown for the Valheim server.";
+    };
+
+    port = lib.mkOption {
+      type = lib.types.port;
+      default = 2456;
+      description = "Base UDP port for the Valheim server.";
+    };
+
+    password = lib.mkOption {
+      type = lib.types.str;
+      description = "Valheim server password.";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      {
+        assertion = cfg.steamPath != null;
+        message = "guests.valheim.steamPath must point at the host directory that stores SteamCMD metadata.";
+      }
+      {
+        assertion = cfg.installPath != null;
+        message = "guests.valheim.installPath must point at the host directory that stores Valheim server files.";
+      }
+      {
+        assertion = cfg.statePath != null;
+        message = "guests.valheim.statePath must point at the host directory that stores Valheim world state.";
+      }
+    ];
+
+    guests.valheim = {
+      interior.modules.services.games.valheim = {
+        enable = true;
+        inherit (cfg) serverName port password;
+        inherit steamDir installDir stateDir;
+      };
+
+      mounts = {
+        ${steamDir} = {
+          directory = cfg.steamPath;
+          owner = config.registry."stable-uid".${config.networking.hostName}.steamcmd;
+          group = "storage";
+          mode = "0770";
+        };
+        ${installDir} = {
+          directory = cfg.installPath;
+          owner = config.registry."stable-uid".${config.networking.hostName}.steamcmd;
+          group = "storage";
+          mode = "0770";
+        };
+        ${stateDir} = {
+          directory = cfg.statePath;
+          owner = config.registry."stable-uid".${config.networking.hostName}.steamcmd;
+          group = "storage";
+          mode = "0770";
+        };
+      };
+
+      limits = {
+        memory = lib.mkDefault "4G";
+        cpu = lib.mkDefault "400%";
+        tasksMax = lib.mkDefault 1024;
+      };
+    };
+  };
+}

configs/nixos/hosts/pikachu/default.nix

@@ -65,21 +65,26 @@
   };
 
   registry.address.pikachu.self = "10.23.10.102";
-  registry.route.pikachu.self = {
-    domain = "valheim.alexion.dev";
-    udp.ports = [
-      config.modules.services.games.valheim.port
-      (config.modules.services.games.valheim.port + 1)
-    ];
-  };
 
-  modules.services.games.valheim = {
+  guests.valheim = {
     enable = true;
-    steamDir = "/pikachu/data/steamcmd";
-    installDir = "/pikachu/data/servers/valheim/main";
-    stateDir = "/pikachu/media/games/servers/valheim/main";
+    vlan = 20;
+    address = "10.23.20.197";
+    steamPath = "/pikachu/data/steamcmd";
+    installPath = "/pikachu/data/servers/valheim/main";
+    statePath = "/pikachu/media/games/servers/valheim/main";
     serverName = "main";
     password = "foobarbaz";
+    reverseProxy = {
+      enable = true;
+      route = {
+        domain = "valheim.alexion.dev";
+        udp.ports = [
+          config.guests.valheim.port
+          (config.guests.valheim.port + 1)
+        ];
+      };
+    };
   };
 
   guests.actualbudget = {