Why Docker?

The original "Docker pitch" (back in 2013!) made a lot of comparisons with the shipping industry, and its transformation thanks to the intermodal shipping container.

More than a decade later... Why is Docker still relevant, and what are we using it for?

Escape dependency hell

Write installation instructions into an INSTALL.txt file
Using this file, write an install.sh script that works for you
Turn this file into a Dockerfile, test it on your machine
If the Dockerfile builds on your machine, it will build anywhere
Rejoice as you escape dependency hell and "works on my machine"

Never again "worked in dev - ops problem now!"

On-board developers and contributors rapidly

Write Dockerfiles for your application components
Use pre-made images from the Docker Hub (mysql, redis...)
Describe your stack with a Compose file
On-board somebody with two commands:

git clone ...
docker compose up

With this, you can create development, integration, QA environments in minutes!

Implement reliable CI easily

Build test environment with a Dockerfile or Compose file
For each test run, stage up a new container or stack
Each run is now in a clean environment
No pollution from previous tests

Way faster and cheaper than creating VMs each time!

Use container images as build artefacts

Build your app from Dockerfiles
Store the resulting images in a registry
Keep them forever (or as long as necessary)
Test those images in QA, CI, integration...
Run the same images in production
Something goes wrong? Rollback to previous image
Investigating old regression? Old image has your back!

Images contain all the libraries, dependencies, etc. needed to run the app.

Devs vs Ops, before Docker

Drop a tarball (or a commit hash) with instructions.
Dev environment very different from production.
Ops don't always have a dev environment themselves ...
... and when they do, it can differ from the devs'.
Ops have to sort out differences and make it work ...
... or bounce it back to devs.
Shipping code causes frictions and delays.

Devs vs Ops, after Docker

Drop a container image or a Compose file.
Ops can always run that container image.
Ops can always run that Compose file.
Ops still have to adapt to prod environment, but at least they have a reference point.
Ops have tools allowing to use the same image in dev and prod.
Devs can be empowered to make releases themselves more easily.

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