Added the actual logic

app/Http/Kernel.php

@@ -2,6 +2,7 @@
 
 namespace Pterodactyl\Http;
 
+use Pterodactyl\Http\Middleware\MaintenanceMiddleware;
 use Pterodactyl\Models\ApiKey;
 use Illuminate\Auth\Middleware\Authorize;
 use Illuminate\Auth\Middleware\Authenticate;
@@ -108,6 +109,7 @@ class Kernel extends HttpKernel
         'can' => Authorize::class,
         'bindings' => SubstituteBindings::class,
         'recaptcha' => VerifyReCaptcha::class,
+        'maintenance' => MaintenanceMiddleware::class,
 
         // Server specific middleware (used for authenticating access to resources)
         //

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);
+    }
+}

app/Models/Node.php

@@ -48,6 +48,7 @@ class Node extends Model implements CleansAttributes, ValidableContract
         'daemonSFTP' => 'integer',
         'behind_proxy' => 'boolean',
         'public' => 'boolean',
+        'maintenance' => 'boolean',
     ];
 
     /**
@@ -62,7 +63,7 @@ class Node extends Model implements CleansAttributes, ValidableContract
         'disk_overallocate', 'upload_size',
         'daemonSecret', 'daemonBase',
         'daemonSFTP', 'daemonListen',
-        'description',
+        'description', 'maintenance',
     ];
 
     /**
@@ -111,6 +112,7 @@ class Node extends Model implements CleansAttributes, ValidableContract
         'daemonBase' => 'regex:/^([\/][\d\w.\-\/]+)$/',
         'daemonSFTP' => 'numeric|between:1024,65535',
         'daemonListen' => 'numeric|between:1024,65535',
+        'maintenance' => 'boolean',
     ];
 
     /**
@@ -126,6 +128,7 @@ class Node extends Model implements CleansAttributes, ValidableContract
         'daemonBase' => '/srv/daemon-data',
         'daemonSFTP' => 2022,
         'daemonListen' => 8080,
+        'maintenance' => false,
     ];
 
     /**

app/Providers/RouteServiceProvider.php

@@ -33,7 +33,7 @@ class RouteServiceProvider extends ServiceProvider
              ->namespace($this->namespace . '\Auth')
              ->group(base_path('routes/auth.php'));
 
-        Route::middleware(['web', 'csrf', 'auth', 'server', 'subuser.auth'])->prefix('/server/{server}')
+        Route::middleware(['web', 'csrf', 'auth', 'server', 'subuser.auth', 'maintenance'])->prefix('/server/{server}')
              ->namespace($this->namespace . '\Server')
              ->group(base_path('routes/server.php'));