Not as painless as I hoped. Or rather, upgrading MySQL versions at the same time is not smooth. If you need legacy platforms and languages and MySQL connector libraries to support the upgrade.
Actually, mostly painless after all. The only pain point I ran into was going from AWS RDS MySQL 5.7 to Ubuntu apt MySQL 5.8. Apparently 5.8 in linux now defaults to expecting table names in queries to be case sensitive. And when MySQL is installed via apt you get no chance to reconfigure that behaviour upon installation, without a semi-hack. From memory you have to stop mysql, delete /var/lib/mysql, change /etc/mysql/mysql.conf/mysqld.cnf to allow insensitive table names, then run an apt command to reinstall/reconfigure mysql. I’ll have to document it properly somewhere.
Apart from that the most onerous parts are similar in all prod system upgrades – stopping db changes, migrating schemas, setting up users/grants, changing DNS, app config, etc pointers, and testing testing testing.
Note to self – this would have been quicker and easier if I hadn’t used to run MySQL on a non standard port for some extra “security by obscurity”