Effective Docker builds

[novemberborn]

I'd like to propose a talk on how best to build Docker images, with a focus of course on building Node applications.

This would cover:

• using official base images
• ordering your Dockerfile to reduce layers and improve build speed
• managing .dockerignore with respect to local builds and CI
• installing dependencies before copying other code
• two-stage builds and slim images
• using dev dependencies at build time but excluding them from the deployed image (and not just "removing" them in the next layer)
• pinning versions (both base images as well as dependencies) so you don't have to worry when you have to update a rarely-changing service

All these are takeaways from deploying Node services at State.

As an example, the Node service powering the website has a rather complicated build process, with ~170 MiB worth of dependencies (including dev), JS & CSS compilation and even invocations of PhantomJS to generate critical path CSS. We can build this into an image that's only 207 MiB, which is about a 6th of the non-slim build.