Optimizing Drupal 9 Performance: Disabling Cache for Controller Routes with Code Examples

Example Code:

1. Define the Route:

   my_module.routing.yml
   my_module.route_name:
     path: '/custom/route'
     defaults:
       _controller: '\Drupal\my_module\Controller\MyController::myMethod'
       _title: 'Custom Route'
     requirements:
       _permission: 'access content'

2. Disable Cache for the Route:

   my_module.services.yml
   services:
     my_module.route_subscriber:
       class: '\Drupal\my_module\Routing\RouteSubscriber'
       tags:
         - { name: 'event_subscriber' }

3. Implement RouteSubscriber:

   MyModule\Routing\RouteSubscriber.php
   namespace Drupal\my_module\Routing;
   
   use Drupal\Core\DependencyInjection\ContainerBuilder;
   use Drupal\Core\DependencyInjection\ServiceProviderBase;
   use Symfony\Component\DependencyInjection\Reference;
   
   /**
    * Modifies the language manager service.
    */
   class RouteSubscriber extends ServiceProviderBase {
   
     /**
      * {@inheritdoc}
      */
     public function alter(ContainerBuilder $container) {
       // Overrides the default DynamicPageCache service for the specified route.
       $definition = $container->getDefinition('dynamic_page_cache.subscriber');
       $definition->setClass('Drupal\my_module\Routing\DynamicPageCacheSubscriber');
     }
   }

4. Create DynamicPageCacheSubscriber:

   MyModule\Routing\DynamicPageCacheSubscriber.php
   namespace Drupal\my_module\Routing;
   
   use Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber as BaseSubscriber;
   use Symfony\Component\HttpKernel\KernelEvents;
   
   /**
    * Listens to the dynamic_page_cache.response event and disables caching for specific routes.
    */
   class DynamicPageCacheSubscriber extends BaseSubscriber {
   
     /**
      * {@inheritdoc}
      */
     protected $priority = 100;
   
     /**
      * {@inheritdoc}
      */
     public static function getSubscribedEvents() {
       $events[KernelEvents::RESPONSE][] = ['onResponse', 100];
       return $events;
     }
   
     /**
      * {@inheritdoc}
      */
     public function onResponse($event) {
       $request = $event->getRequest();
   
       // Disable cache for the specified route.
       if ($request->attributes->get('_route') == 'my_module.route_name') {
         $event->getResponse()->headers->set('Cache-Control', 'no-cache, no-store, must-revalidate');
       }
     }
   }

By following these steps, you can selectively disable caching for specific controller routes in Drupal 9, optimizing your website's performance.