Precompile Ruby on Rails assets with Docker

build.sh

docker build --build-arg="ASSET_HOST=http://mycdn/path-to-assets" .

Dockerfile

ARG ASSET_HOST
RUN bundle exec rake ASSET_HOST=${ASSET_HOST} RAILS_ENV=production assets:precompile

production.rb

  # Enable serving of images, stylesheets, and JavaScripts from an asset server.
  config.action_controller.asset_host = ENV['ASSET_HOST']

push_assets.sh

mkdir -p rails_assets
id=$(docker create <my_image_with_assets>)
docker cp $id:/app/public/assets rails_assets
aws s3 cp --recursive rails_assets/ s3://<my_s3_bucket_name> --cache-control max-age=604800