Deploying releases within containers

howto.txt

This is not meant to be comprehensive, a guide, or anything quite that sophisticated, just a couple
notes on what I do at work, in production, and how my environment is set up.

Overview:

- Infrastructure runs on AWS
- We run an internal PaaS based on OpenShift Origin/Kubernetes
- We push code to GitHub, which triggers a webhook, which in turn
  triggers OpenShift to start a build, which fetches the source
  code, and runs the build using the Dockerfile contained in the
  root of the project.
- When a build completes, it pushes the image to an imagestream,
  which is an OpenShift primitive representing a stream of changes
  to a given image name. It's basically just named/tagged Docker images.
- However, the imagestream gives us some nice capabilities, by default
  images get tagged with 'latest', but we also have tags for 'staging' and
  'prod' which allow us to tag a given image from the 'latest' stream, and
  have it automatically promote to the tagged environment. We use this to
  tag images into staging, and into production.
- We're not doing hot upgrades, we use rolling releases.
- Configuration is done primarily via environment variables set via Kubernetes

Releases:

- Our Elixir/Erlang releases are built using my bitwalker/alpine-erlang base image
  from Docker Hub.
- Our project Dockerfiles look something like this: https://gist.github.com/bitwalker/3f5fe253f81d9942a29f2bf26084acd5
- In short, we install Elixir, fetch deps, compile, build the release, copy it to a target directory,
  set permissions, then strip out the source code and the build-time deps (i.e. Elixir) and we are left
  with an image which only contains the release.