Dockerfile.erb - use ruby in your dynamic Dockerfile

Install

gem install dockerb

or standalone

curl https://rubinjam.herokuapp.com/pack/dockerb > dockerb && chmod +x dockerb

Usage

docker generates a Dockerfile from your Dockerfile.erb (delete it after building / do not commit it)

custom

RUN echo <%= "hello" + " " + "world" %>
---
RUN echo hello world

install_gem

Pre-install a slow gem so re-building the container is fast

• picks the correct version from Gemfile.lock
• use before Adding Gemfile.lock or bundling

<%= install_gem 'nokogiri' %>
---
RUN gem install -v 1.6.3 nokogiri

bundle

• add as little as necessary to bundle
• do not fail when re-locking fails due to git not being installed (|| bundle check)

<%= bundle %>
---
ADD Gemfile /app/
ADD Gemfile.lock /app/
ADD vendor/cache /app/vendor/cache
RUN bundle install --quiet --local --jobs 4 || bundle check

Inside of ruby:

Dockerb.compile do
  ... do other things ...
end
# Dockerfile is cleaned up

Author

Michael Grosser
michael@grosser.it
License: MIT