What is Docker?

Docker allows you to package an application with all of its dependencies into a standardized unit for software development.

This means dev/prod parity!

😅

It also means saying goodbye to tools like...

• rvm
• nvm
• pyenv
• virtualenv

Images and Containers

Containers are not VMs

The analogy we use here at Docker is comparing houses (virtual machines) to apartments (Docker containers).

Want to dig deeper?

• Read Eric Chiang's Containers From Scratch
• Watch Jérôme Petazzoni's Cgroups, namespaces, and beyond: what are containers made from?
• If you're on OS X or Windows, watch Justin Cormack's Docker for Mac and Windows: The Insider's Guide

For details on why the “shipping container” metaphor is apt, listen to Planet Money Episode 500: The Humble Innovation At The Heart Of The Global Economy (18 minutes).

Super simple demo

docker run -it --rm alpine:3.4 sh

Try apk update && apk add nano in there.

When you exit the container, nano disappears, as do any of your changes to the filesystem.

😖

Optimally Docker containers are completely stateless and immutable.

Less simple demo

Check out 18F/atul-docker-presentation/flask-example!