Skip to Content

A stick figure smiling

Here's a preview from my zine, How Containers Work!! If you want to see more comics like this, sign up for my saturday comics newsletter or browse more comics!

Image of a comic. To read the full HTML alt text, click "read the transcript".

browse more comics! get the zine!
read the transcript!

different images have similar files

Rails container image and Django container image: we both use Ubuntu 18.04!

reusing layers saves disk space

Rails image:
Rails app

Django image: Django app

exact same files on disk!

a layer is a directory

$ ls 8891378eb*
boot/lib/ opt sbin/ usr/ dev/lib64/proc/srv/var/
etc/media/ root/sys/

files in an ubuntu:18.04 layer

every layer has an ID

usually the ID is a sha256 hash of the layer’s contents example: 8e99fae2..

if a file is in 2 layers, you’ll see the version from the top layer

/code/ (this is the version you’ll see in the merged image) /code/

by default, writes go to a temporary layer

temp layer (these files might be deleted after the container exits)

To keep your changes, write to a directory that’s mounted from outside the container

Saturday Morning Comics!

Want another comic like this in your email every Saturday? Sign up here!

I'll send you one of my favourite comics from my archives every Saturday.
© Julia Evans 2024 | All rights reserved (see the FAQ for notes about licensing)