Issue #2453351 by effulgentsia, Wim Leers: Maintenance mode message ends up in...

Issue #2453351 by effulgentsia, Wim Leers: Maintenance mode message ends up in page cache, served endlessly

core/lib/Drupal/Core/EventSubscriber/MaintenanceModeSubscriber.php

@@ -98,6 +98,8 @@ public function __construct(MaintenanceModeInterface $maintenance_mode, ConfigFa
   public function onKernelRequestMaintenance(GetResponseEvent $event) {
     $route_match = RouteMatch::createFromRequest($event->getRequest());
     if ($this->maintenanceMode->applies($route_match)) {
+      // Don't cache maintenance mode pages.
+      \Drupal::service('page_cache_kill_switch')->trigger();
       if (!$this->maintenanceMode->exempt($this->account)) {
         // Deliver the 503 page if the site is in maintenance mode and the
         // logged in user is not allowed to bypass it.

core/modules/system/src/Tests/System/SiteMaintenanceTest.php

@@ -38,10 +38,31 @@ protected function setUp() {
     $this->drupalLogin($this->admin_user);
   }
 
+  /**
+   * Verify site maintenance mode functionality with page cache disabled.
+   */
+  function testSiteMaintenanceWithoutPageCache() {
+    $config = $this->config('system.performance');
+    $config->set('cache.page.use_internal', 0);
+    $config->save();
+    $this->doTestSiteMaintenance();
+  }
+
+  /**
+   * Verify site maintenance mode functionality with page cache enabled.
+   */
+  function testSiteMaintenanceWithPageCache() {
+    $config = $this->config('system.performance');
+    $config->set('cache.page.use_internal', 1);
+    $config->set('cache.page.max_age', 300);
+    $config->save();
+    $this->doTestSiteMaintenance();
+  }
+
   /**
    * Verify site maintenance mode functionality.
    */
-  function testSiteMaintenance() {
+  protected function doTestSiteMaintenance() {
     // Turn on maintenance mode.
     $edit = array(
       'maintenance_mode' => 1,