I have a D8 site since some months. Today I realised that I needed drush in order to migrate some contents (using the migrate tools module). Composer was not installed, so I installed it. Then I installed drush (version 9) and it seems to work but the drush command defined in migrate tools are not working. I have noticed that when I do a drush cc, I can only clear the drush cache. Like if drush didn't see my drupal installation.
What did I miss ?