Added the actual logic

app/Http/Middleware/MaintenanceMiddleware.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Pterodactyl\Http\Middleware;
+
+use Closure;
+
+class MaintenanceMiddleware
+{
+    /**
+     * Handle an incoming request.
+     *
+     * @param  \Illuminate\Http\Request  $request
+     * @param  \Closure  $next
+     * @return mixed
+     */
+    public function handle($request, Closure $next)
+    {
+        $server = $request->attributes->get('server');
+        $node = $server->node;
+
+        if ($node->maintenance) {
+            return response(view('errors.maintenance'));
+        }
+
+        return $next($request);
+    }
+}