As many of you will know, the world of ops and infrastructure is a matter of read the manual, try, get it wrong, repeat cycle.  That's great if the thing you are working with is a physical piece of hardware with clear instructions that do work.  Software Emulated hardware can have some interesting side effects as I soon found out when using Docker containers to host MySQL and Glassfish.

MySql

The official download from hub.docker does have very clear instructions, but me being me, I didn't read the writing on the tin, especially the section "Using a custom MySQL configuration".