Test-Driven Development with Python, 3rd Edition

Chapter 9. Containerization aka Docker

Little boxes, all the same

Malvina Reynolds

In this chapter, we’ll start by adapting our FTs so that they can run against a container. And then we’ll set about containerising our app, and getting those tests passing our code running inside Docker:

• We’ll build a minimal Dockerfile with everything we need to run our site.

• We’ll learn how to build and run a container on our machine.

• We’ll make a few changes to our source code layout, like using a src folder.

• We’ll start flushing out a few issues around networking and the database.

Docker, Containers, and Virtualization

Docker is a commercial product that wraps several free and open source technologies from the world of Linux, sometimes referred to as “containerization”.

Note

Feel free to skip this section if you already know all about Docker.

You may have already heard of the idea of “virtualization”, which enables a single physical computer to pretend to be several machines. Pioneered by IBM (amongst others) on mainframes in the 1960s, it rose to mainstream adoption in the ’90s, where it was sold as a way to optimise resource usage in datacentres. AWS, for example, an offshoot of Amazon, was using virtualization already, and realised it could sell some spare capacity on its servers to customers outside the business.

So, when you come to deploy your code to a real server in a datacentre, it will be using virtualization. And, actually, you can use virtualization on your own machine, ...