We updated our Linux VM from Ubuntu 16.04 to 18.04 so that we could be ready for another few years without problems.
Unfortunately the update reset the config file so we had to hunt around to fix it.
sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf
We had to change bind-address = 127.0.0.1 to 0.0.0.0 so our sites would connect, fixed
sudo service mysql restart
and we are live.
we use a very strong password for the root of the MySQL server so it is not a major security risk