Docker for DevOps Roadmap

Docker is easy to use and hard to use well, and the gap between those shows up as builds that take four minutes when they should take ten seconds, images that ship your AWS keys in a layer nobody looks at, and a container that runs on your laptop and not in CI.

The order here follows how the abstraction is built. Images and layers first, because the layer cache explains most of what is otherwise mysterious about build times and image size — including why reordering two lines in a Dockerfile can change a rebuild from minutes to seconds.

Networking and volumes come before Compose, because Compose is mostly a declarative wrapper over exactly those two things plus process ordering. Learning Compose first gives you a file you can edit but not debug.

Registries and CI come last, since pushing an image is the easy part once the image is right.