feat: add nginx upstream proxy module

modules/nixos/upstream-proxy.nix

@@ -0,0 +1,60 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}: let
+  cfg = config.tux.services.nginxStreamProxy;
+
+  upstreamServerType = lib.types.submodule ({config, ...}: {
+    options = {
+      address = lib.mkOption {
+        type = lib.types.str;
+        description = "IP address or hostname of the upstream server";
+      };
+      port = lib.mkOption {
+        type = lib.types.port;
+        default = 9999;
+        description = "Port number of the upstream server";
+      };
+      listenPort = lib.mkOption {
+        type = lib.types.port;
+        default = config.port;
+        defaultText = lib.literalExpression "port";
+        description = "Local port to listen for incoming connections (defaults to port)";
+      };
+    };
+  });
+in {
+  options.tux.services.nginxStreamProxy = {
+    enable = lib.mkEnableOption "Enable nginx TCP stream proxy";
+
+    upstreamServers = lib.mkOption {
+      type = lib.types.listOf upstreamServerType;
+      default = [
+        {
+          address = "0.0.0.0";
+          port = 9999;
+        }
+      ];
+      description = "List of upstream servers to proxy to, each with its own listen port";
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    networking.firewall.allowedTCPPorts = map (server: server.listenPort) cfg.upstreamServers;
+
+    services.nginx = {
+      enable = lib.mkForce true;
+      package = pkgs.nginx.override {withStream = true;};
+      streamConfig =
+        lib.concatMapStringsSep "\n" (server: ''
+          server {
+            listen ${toString server.listenPort};
+            proxy_pass ${server.address}:${toString server.port};
+          }
+        '')
+        cfg.upstreamServers;
+    };
+  };
+}