Building Docker images usually takes a long time. This repo contains base images with preinstalled dependencies for Ruby on Rails, so building a production image will be 2-3 times faster.

When using the official Ruby image, building a Docker image for a typical Rails application requires lots of time for installing dependencies - mainly OS packages, Ruby gems, Ruby gems with native extensions (Nokogiri etc.) and Node modules. This is required every time the app needs to be deployed to production.

I was looking for a way to reduce this time, so I created base images that contain most of the dependencies used in my applications.

And while I'm at it, I also moved as much as possible from the app-specific Dockerfile into the base image by using ONBUILD triggers. This makes the Dockerfile in my apps small and simple.

I compared building times using a typical Rails application. This is the result on my local machine:

• Based on official Ruby image: 4:50 min
• Based on DockerRailsBase: 1:57 min

As you can see, using DockerRailsBase is more than 2 times faster compared to the official Ruby image. It saves nearly 3min on every build.

Note: Before I started timing, the base image was not available on my machine, so it was downloaded first, which took some time. If the base image is already available, the building time is only 1:18min (3 times faster).

This repo is based on the following assumptions:

• Your app is compatible with Ruby 2.7.1 for Alpine Linux
• Your app uses Ruby on Rails 6
• Your app uses PostgreSQL
• Your app installs Node modules with Yarn
• Your app compiles JS with Webpacker and/or Asset pipeline (Sprockets)

To build a very small production image, multi-stage building is used. There are two Dockerfiles in this repo, one for the first stage (called "Builder") and one for the resulting stage (called "Final").

Used for installing Ruby gems and Node modules. Includes Git, Node.js and some build tools - all we need to compile assets.

• Based on ruby:2.7.1-alpine
• Adds packages needed for installing gems and compiling assets: Git, Node.js, Yarn, PostgreSQL client and build tools
• Adds some standard Ruby gems (Rails 6 etc., see Gemfile)
• Adds some standard Node modules (Vue.js etc., see package.json)
• Via ONBUILD triggers it installs missing gems and Node modules, then compiles the assets

See Builder/Dockerfile

Used to build the production image which includes just the minimum.

• Based on ruby:2.7.1-alpine
• Adds packages needed for production: postgresql-client, tzdata, file
• Via ONBUILD triggers it mainly copies the app and gems from the "Builder" stage

See Final/Dockerfile

Using Dependabot, every updated Ruby gem or Node module results in an updated image.

FROM ledermann/rails-base-builder:latest AS Builder
FROM ledermann/rails-base-final:latest
USER app
CMD ["bundle", "exec", "puma", "-C", "config/puma.rb"]

Yes, this is the complete Dockerfile of the Rails app. It's so simple because the work is done by ONBUILD triggers.

Docker supports layer caching, so for building images it performs just the needed steps: If there is a layer from a former build and nothing has changed, it will be used. But for dependencies, this means: If a single Ruby gem in the application was updated or added, the step with bundle install is run again, so all gems will be installed again.

Using a prebuilt image improves installing dependencies a lot, because only the different/updated dependencies will be installed - all existing ones will be reused.

This doesn't matter:

• A missing Alpine package can be installed with apk add inside your app's Dockerfile.
• A missing Node module (or version) will be installed with rails assets:precompile via the ONBUILD trigger.
• A missing Ruby gem (or version) will be installed with bundle install via the ONBUILD trigger.

No. In the build stage there is a bundle clean --force, which uninstalls all gems not referenced in the app's Gemfile.