Wednesday, February 18, 2015

MySQL on Docker

Numerous articles were written on how Docker is going to change the IT as we know it. Removing the need for full/para virtualization and configuration management frameworks.

While these statements are a bit exaggerated in my opinion, it seems that the technology is here to stay and is being rapidly adopted especially by the SaaS/web companies for obvious reasons such as portability and lower footprint than traditional Hypervisors.

In this short post I'd like to present a small "Howto" on running a MySQL (now MariaDB) DB on a Docker container, and present you some potential pitfalls ,so let's get started...

We will create a Docker file, which is our bootstrapping manifest for our DB image:

OK, so what we go here? We are pulling an Ubuntu image out of the Docker repository, installing the server and making sure the it is not bound to 'localhost', with some 'sed' magic, all in all pretty standard.

If more modifications were required for my.conf (and in real life scenario this would probably be mandatory), obviously 'sed' will be an ugly way to modify it so we could create a local copy of my.conf, make all the modification , add it to our Docker file and run the build process:

At this point we will be able to connect both from host and from other containers through a TCP socket:

But what about data persistence?  Remember that all the local data that is currently running in the container is ephemeral... While we could do something as:
This would delete our system data (tables with metadata), so what's the solution?

We need to add a wrapper script that will re-initialize the db in case there is no metadata available. The script can be added to the Docker file via 'ADD' statement:

That's better, now our DB runs on a persistent storage (/data/mysql - on the host machine which can be external SAN or NAS storage).