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DOCKER.md

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This page is archived. Please visit https://countable-ops-manual.readthedocs.io/

Countable Docker Guide

We have some training materials on Docker here

We use Docker to manage dev, test, stage and prod environments. Specific conventions we follow:

  • It should be as easy and quick as possible to set up a new environment.
  • production and development environments should be as similar as possible (or, as practical anyway).
  • Base your Dockerfiles on official dockerhub.com images where they exist.
  • docker-compose.yml contains the Docker config which is the same between every environment.
  • A file called dc.dev.yml should exist with any settings that vary between environments. In a dev environment, to set up you would copy it and modify it locally with cp dc.dev.yml docker-compose.override.yml. Similar for dc.stage.yml and dc.prod.yml for other environments respectively. Our CI testing environments can use dc.dev.yml. docker-compose.override.yml should be in .gitignore
  • The docker-compose.override.yml file should only contain differences between dev and prod and other environments. This includes the ports, restart policy, secrets, and normally not much else. If a line doesn't need to be in the overrides for a specific reason, move it to the main docker-compose.yml instead.

Setting Up An Environment

  1. Install Docker on your machine

  2. Clone one of our beautiful apps. git clone <repo>

  3. Copy the docker override template: cp dc.dev.yml docker-compose.override.yml

  4. Run docker-compose: docker-compose up

  5. Navigate to http://localhost. Ensure only one project is running at a time if you're using port 80 (as we do here)

Editing the Dockerfiles

When you change something about the operating system environment your container exposes, such as installing a new package, this is often done in the Dockerfile itself. This will result in changes being propagated to other environments including production when you commit the modified Dockerfile, triggering a Docker build there. However, if you modify a file used during the build step such as requirements.txt , other environments won't be updated by default. To force environments to rebuild, commit a small change to the Dockerfile. Our convention is:

RUN echo "bust cache 33 (version)"

Bumping this version will trigger the rebuild as desired.

Troubleshooting

When starting with Docker there are a few common issues:

  • A port you need is blocked. Typically our apps run on port 80. To see if something's running there, sudo lsof -n -i :80 | grep LISTEN on Linux, Mac.
  • Make sure you have a docker-compose.override.yml with port 80 mapped to your application.