Systemd mysql service unit (alias) reported as inactive while it should be reported as active

Under Debian Stretch, the MariaDB server comes with the mariadb service unit:

• /lib/systemd/system/mariadb.service

The mysql and mysqld service units are also provided as aliases (alternative names):

• /etc/systemd/system/mysql.service (symlink to /lib/systemd/system/mariadb.service)
• /etc/systemd/system/mysqld.service (symlink to /lib/systemd/system/mariadb.service)

In our environment we have a cron task that is responsible to renew our let's encrypt SSL certificates. That cron task check that the mysql service is running prior doing anything else and exit if the service is not running. We execute the following command to check the service:

systemctl is-active mysql

Lately, one of our certificate has not been renewed. After some investigation, we have found that the command above report the mysql service as inactive while it is active. However, the same command on the mariadb service unit report the service as active.

Executing the systemctl status mysql command seem to solve the problem because when re-running the systemctl is-active mysql command just after, the service is reported as active. That is really a weird issue.