I'm real late to the docker game, but listenting to the Self Hosted podcast recently has helped me realize the simplicity of this configuration.  Well, simple once  you understand it.  I spent the day today moving my native webservices to docker.  Here's how it went

Things I needed to move and make work

• TikiWiki - been running this CMS for 18 years now.  Iit has to go with me
• mariadb - it currently holds greyhole and tiki dtabases
• greyhole connection to mariadb
• nextcloud - I don't really need this, but I have it running in a standalong container and I want it in DC

It took me all day to get a working config just for mariadb.  All the issues were authentication related once the db spun up in a container.  Here's what I think I know:

• apps in a container connect using "%" as the host
• apps outside a container use localhost

Greyhole was a special case.  Since mariadb is in a container, localhost no longer works as a db_host.  I changed it to 127.0.0.1 and it worked fine.  One other issue - retstarting the docker-compose disconnects the session and greyhole must be restarted. I may consider a separate mariadb instance for this

For mariiadb migration, I was hoping if i simply mounted the physical mariadb folder into th container, that the container version would just use it, but that didn't work.  I h ad to dump and import the existing data and recreate users.