How do I set up a site to use Redis as cache handler?
For Drupal 8, use this code in the settings.php file:

$settings['redis.connection']['host'] = 'localhost';
$settings['redis.connection']['port'] = NULL;
$settings['cache']['default'] = 'cache.backend.redis';
$settings['redis.connection']['base'] = 101;


You can check whether or not Redis is running by viewing the status report at: /admin/reports/status