How can I check if the redis module is enabled in settings.php?

Question

I've read How can I check if a module is enabled? and How can we use \Drupal class inside Settings.php and came to the conclusion that I cannot use the module_handler service in settings.php.

How can I check if a module -- in this case the redis module -- is enabled in settings.php?

Context

I am using docker for a Drupal 9.4 installation. When I initialize a new container from the image, and I install Drupal (initialize a new database), the redis module isn't initially activated, although present.

This means I cannot initially specify $settings['cache']['default'] = 'cache.backend.redis'; in settings.php (it will make the system crash).

I would have like to do

$moduleHandler = \Drupal::service('module_handler');
if ($moduleHandler->moduleExists('redis')) {
  $settings['cache']['default'] = 'cache.backend.redis';
}

Of course this doesn't work and I understand why. But I would like to avoid going into my container to edit settings.php after activating the redis module every time I start a new container.

Answer 1

The answer to this precise question is now part of the Redis module:

use Drupal\Core\Installer\InstallerKernel;
if (!InstallerKernel::installationAttempted() && extension_loaded('redis')) {
  $settings['cache']['default'] = 'cache.backend.redis';
  //etc
} 

Answer 2

For the same reasons mentioned in How can we use \Drupal class inside Settings.php, namely that the Drupal bootstrap process hasn't completed yet, this cannot be done.

see @Jaypan's comment.