Drush 9 can't find installed module, yields CommandNotFoundException On my newly installed Drupal 8.4.4 sandbox installation, I've installed Drush 9 and the Devel module:

composer require drush/drush:^9
composer require drupal/devel


After running these commands, I installed the Devel module using the Extend tab in Drupal.

Drush seems be be installed correctly:

www-data@39e134dc7690:~/html$ /var/www/html/vendor/bin/drush version
Drush version : 9.1.0


The Devel modules seems to be installed correctly: 

www-data@39e134dc7690:~/html$ grep -r devel-container-service /var/www/html/modules/contrib/devel/
/var/www/html/modules/contrib/devel/src/Commands/DevelCommands.php:   * @aliases devel-container-services,dcs,devel-services
/var/www/html/modules/contrib/devel/drush/devel.drush8.inc:  $items['devel-container-services'] = array(


But Drush doesn't seem to find the devel module: 

www-data@39e134dc7690:~/html$ /var/www/html/vendor/bin/drush devel-container-services
[Symfony\Component\Console\Exception\CommandNotFoundException]
Command "devel-container-services" is not defined.


Are there any path settings I need to tweak to get Drush to find the Devel module?
I looks like I simply had forgotten to enable (i.e install) the module in /admin/modules. I had just ran "composer require", but not actually enabled it.