Upgrading MySQL in a Container

Upgrading MySQL 5.5 to 5.7 in a docker container set caused me some trouble. Setting the tag to 5.7.30 was all well and good but when I fired up the container MySQL would stop immediately.

Looking at the log I found The table is probably corrupted and references to run mysql_upgrade which I was expecting to have to do, but how do you do that when the service fails to start and the container is offline?

I needed to run my container and start mysqld manually by going into a bash shell as the user mysql (my container service is called ‘db’).

docker-compose run --rm -u mysql db bash
mysql --skip-grant-tables &
mysql_upgrade -uroot

It is important you start mysqld with the & to spawn a background process so that you can then call the upgrade command. The upgrade will take a while and seems to pause at regular intervals.

If you bork something you can stop the docker process, but you will then need to delete the Unix socket in order to try again, eg.

docker stop name_db_run_1
sudo rm /srv/container-volumes/name/socket/mysqld.*