Question

We have a Rails 3.1 app that allows users to upload photos to Amazon S3. Since we’re using S3 in production I’d like to automatically (on cap deploy) also upload the precompiled assets (application.js & application.css & images) to our S3 bucket where they’ll be served. Simple enough.

Beyond setting config.action_controller.asset_host = "http://assets.example.com"

In short, I’m looking for some examples of a working “recipe” for Capistrano to do so but can’t seem to find any modern (3.1 asset pipeline compatible) ones. We are successfully precompiling the assets but how to move them to S3? And, ideally, only the ones that have changed?

“Meat” of current “recipe”:

...

after "deploy:update_code", "deploy:pipeline_precompile"
before "deploy:finalize_update", "deploy:copy_database_config"

namespace :deploy do
  task :start do ; end
  task :stop do ; end
  task :restart, :roles => :app, :except => { :no_release => true } do
    run "#{try_sudo} touch #{File.join(current_path,'tmp','restart.txt')}"
  end

  # copy database.yml into project
  task :copy_database_config do
    production_db_config = "/path_to_config/#{application}.yml"
    run "cp #{production_db_config} #{current_release}/config/database.yml"
    `puts "replaced database.yml with live copy"`
  end
  task :pipeline_precompile do
    run "cd #{release_path}; RAILS_ENV=production bundle exec rake assets:precompile"
  end
end

Answer 1

While this doesn’t directly answer the question of uploading your assets to S3 on deploy, I think the following approach may address your goals and be a little simpler to implement.

The primary benefits of hosting assets on S3 and using the config.action_controller.asset_host directive include (among others):

• allowing additional simultaneous downloads of assets
• serving assets from a cookie-free domain

Rather than using s3, you can use the CloudFront CDN to achieve the same benefits. The new rails asset pipeline plays very nicely with CloudFront. Here are the steps I am currently using in production:

Create a new CloudFront distribution

1. Delivery Method should be Download
2. Choose Custom Origin and point it to your web server
3. For Distribution Details you can add addition CNAME records such as cdn01.mydomain.com etc.
4. Default Root Object can be left empty

If your site is served over SSL, you will need to use the x12whx1751nfir.cloudfront.net style hostname as custom certificates are not available yet as they are with ELB and your users will see certificate hostname mismatch errors. If you don’t use SSL, you can use the either the default hostname or any CNAMEs prodvided.

Once this is setup, the initial object requests will be fetched from your server and placed within CloudFront. The digest fingerprints generated by the asset pipeline will handle your requirement for only sending assets which have changed.