How Containers Work!

by Julia Evans

When you first start using containers, they seem really weird. Is it a process? A virtual machine? What’s a container image? Why isn’t the networking working? I’m on a Mac but it’s somehow running Linux sort of? And now it’s written a million files to my home directory as root? What’s HAPPENING?

And you’re not wrong. Containers seem weird because they ARE really weird. They’re not just one thing, they’re what you get when you glue together 6 different features that were mostly designed to work together but have a bunch of confusing edge cases.

This zine explains EXACTLY what happens when you run a container on your computer. It turns out that there are only a few big ideas you need to understand what’s going on (images! overlay filesystems! capabilities! pivot_root! cgroups! namespaces! seccomp-bpf!).

Once you understand these fundamentals, you’ll be able to go from “um, my container got killed??? why??? help!!!” to “oh, we set the cgroup memory limit too low! I’ll just look up how to adjust it!”

24 pages, ebook

First published April 24, 2020

Reviews

[Paweł Cisło · Rating 4 out of 5]

One can read this brief zine in less than an hour while finally getting his head around the idea of containers. Most of the scenarios presented in this e-book shall make the containerization features clear, although the more advanced ones will still require a further read.