The database is not bootstrapped in another docker container The following problem occurs when running certain Drush commands, such as drush en features which outputs:  


  Command pm-enable needs a higher bootstrap level to run - you will need to invoke drush from a more functional Drupal environment to run this command.
  The drush command 'en features' could not be executed.
  Drush was not able to start (bootstrap) the Drupal database.
  Hint: This may occur when Drush is trying to:  
  
  
  bootstrap a site that has not been installed or does not have a configured database. In this case you can select another site with a working database setup by specifying the URI to use with the --uri parameter on the command line. See drush topic docs-aliases for details.  
  connect the database through a socket. The socket file may be wrong or the php-cli may have no access to it in a jailed shell. See http://drupal.org/node/1428638 for details.
  
  
  Drush was attempting to connect to:
  
  Drupal version: 7.58
  Site URI: http://default
  Database driver: mysql
  Database hostname: mysql
  Database port:
  Database username: default
  Database name: default
  PHP executable:  /usr/bin/php
  PHP configuration: /etc/php/7.2/cli/php.ini
  PHP OS: Linux
  Drush script: /var/www/vendor/drush/drush/drush.php
  Drush version: 8.1.17
  Drush temp directory: /tmp
  Drush configuration:
  Drush alias files:
  Drupal root: /var/www
  Drupal Settings File: sites/default/settings.php
  Site path:  sites/default


This problem has been reported previously, but in different contexts, not in the specific setup I am working with, which consists of separate docker containers on a linux hosting server.


Apache 2
ElasticSearch
Workspace
PHP
MySQL


All the docker containers are running, as well as the (development) website that is built with drupal, which does connect to the database. Drush had previously been used for setting things up, but something seems to have broken during the development process. Drush had been added to the project using composer, as suggested on Install a site-local Drush and Drush Launcher.

The error seems independent of the directory where the command is executed. Moreover, the settings.php file exists at the path mentioned in the output above and contains the correct database configuration. 

Finally, drush sql-cli returns the following message.


  sh: 1: mysql: not found
  SQL client error occurred.


Do you have any idea on what the problem might be?
Ok, this is solved now, thanks to leymannx and hansfn. I had to also install mysql-client in the workspace container, where drush was being executed from, in addition to the mysql-server running in its own container; mysql-client must have previously been present in the workspace container for a different reason, but some containers were stopped and restarted at some point, so any container-specific installations must have disappeared.