How to use max-age

Question

Here's a simple "Hello World" controller. It's working correctly, except for the "max-age" statement. The request returns a Drupal cache hit every time after the first request, rather than just for 5 seconds. I've tried to find a simple example of how to do this but haven't had much luck. If anyone could help, that would be very much appreciated.

<?php
/**
 * @file
 * Contains \Drupal\hello_world\Controller\HelloController.
 */

namespace Drupal\hello_world\Controller;
use Drupal\Core\Controller\ControllerBase;

class HelloController extends ControllerBase {

  public function content() {

    return array(
      '#type' => 'markup',
      '#markup' => $this->t('Hello, World!'),

      // THIS ISN'T WORKING:
      '#cache' => array("max-age" => 5),
    );
  }
}
?>

Answer 1

The page cache module doesn't respect max-age. Unfortunate but the problem is that Drupal usually contains elements like forms that are by default set to max-age 0, but that only applies to authenticated users most of the time.

To invalidate the page cache, you need to use cache tags, which you invalidate when something changes.

If that doesn't work, you can try to set the Expires header on the response, but for that you either need to return a Response object or alter it in an event when it has been created.

Note: max-age does work for dynamic page cache (authenticated users), rendered blocks, views, entities and so on. Just not for the anonymous page cache.