How to condition output based on a URL query string

Question

In my node preprocess function I check the value of a query param...

$variables['exclude_urls'] = \Drupal::request()->get('exclude_urls');

And in my template, I have...

{% if not exclude_urls %}
  <div class="gr-url">{{ url }}</div>
{% endif %}

However, this approach doesn't work because the node preprocess function does not fire if nothing in the URL changes besides the value for the 'exclude_urls' param.

I have tried various methods to disable caching for the page. Adding this to the route doesn't work...

  options:
    no_cache: 'TRUE'

I also tried using the page_cache_kill_switch in my controller, but it doesn't work...

\Drupal::service("page_cache_kill_switch")->trigger();

Neither does adding the query parameter to cache contexts...

$element['#cache']['contexts'][] = 'url.query_args:exclude_urls';

Instead of using hook_preprocess_node, is there some other way I should be checking the value of $_GET['exclude_urls'] and passing that to the template? Do I add code to the twig template itself to check the value of 'exclude_urls'? Is there any sure way to force hook_preprocess_node to fire every time? What is the usual approach to conditioning display of content based on a URL query param so that caching won't interfere?

Update: To be clear, I have also tried the above approaches in combination, with no success. For example, the end of my page function in my controller looks like this...

\Drupal::service("page_cache_kill_switch")->trigger(); 
$element['#cache']['contexts'][] = 'url.query_args:exclude_urls';
return $element;

Update 2: In my local dev site, I do not experience this problem, and I've found that this line in my local settings makes it so hook_preprocess_node fires every time...

$settings['cache']['bins']['render'] = 'cache.backend.null';

However, I'm not sure how to take advantage of this in my production site, since I don't want to disable the render cache generally. I can do something like this in settings.php, but it's a hack:

$parts = explode('?', $_SERVER['REQUEST_URI'], 2);
if ('/disable/cache/at/this/path' == $parts[0]) {
  $settings['cache']['bins']['render'] = 'cache.backend.null';
}

Answer 1

There are three layers where rendered content can be cached:

• The Page Cache, which stores complete pages based on the URL for anonymous users.
• The Dynamic Page Cache, which stores pages with placeholders for dynamic content that is rendered on each request.
• The Render Cache, which stores individual rendered elements.

Each has a corresponding cache bin that can be disabled during development in settings.php

---

To set an additional cache context in hook_preprocess, so that the Dynamic Page cache knows to re-render that fragment and the render cache stores variants as needed, update the #cache variable:

function hook_preprocess_HOOK(&$variables) {
  $variables['#cache']['contexts'][] = 'url.query_args:exclude_urls';
}