Uploads static assets to Amazon S3 with unique identifiers encoded into the path of the asset.

Only works with Rails 3.x because Rails 3 makes doing this sort of thing a lot easier and
that is all I needed it for.

This library takes standard Rails asset paths such as /stylesheets/main.css?1288717704 and converts them
into https://my_bucket.s3.amazonaws.com/stylesheets/main-id-95df8d9bf5237ad08df3115ee74dcb10.css.

It uses an MD5 hash of the file contents to produce the id so the same asset will always have the same ID.

In my quest to achieve a Google Page Speed score of 100, this library achieves the following:

• Assets served from a cookie-less domain
• Unique identifier is not encoded into a query parameter (so it is cacheable by proxy servers)
• All assets have far-future expires headers for caching
• Assets have the Cache-Control: public header for caching
• CSS and javascript is GZipped and the correct headers are added

As an added bonus, all your assets are available over https:// as well.

Add the gem to your Gemfile

gem "asset_id"

Configure config/environments/production.rb to use Amazon S3 as the asset host
and to use the id-stamped asset paths in helpers

config.action_controller.asset_host = Proc.new do |source|
 'https://my_bucket.s3.amazonaws.com'
end
config.action_controller.asset_path = Proc.new do |source|
 AssetID::Asset.fingerprint(source)
end

Add your Amazon S3 configuration details to config/asset_id.yml

production:
  access_key_id: 'MY_ACCESS_KEY'
  secret_access_key: 'MY_ACCESS_SECRET'
  bucket: "my_live_bucket"

Optionally create a rake task in lib/tasks/asset_id_tasks.rake to
perform the upload for use in your deploy scripts

namespace :asset do
  namespace :id do
    
    desc "uploads the current assets to s3 with stamped ids"
    task :upload do
      AWS::S3::DEFAULT_HOST.replace "s3-eu-west-1.amazonaws.com" # If using EU bucket
      AssetID::Asset.asset_paths += ['favicon.png'] # Configure additional asset paths
      AssetID::S3.upload
    end
    
  end
end

If you want to use the SSL host in your configuration you can do so in config/environments/production.rb

config.action_controller.asset_host = Proc.new do |source|
  request.ssl? 'https://my_bucket.s3.amazonaws.com' : 'https://my_bucket.s3.amazonaws.com'
end

By default any relative CSS images that match files on the filesystem are converted to AssetID paths as well.

For S3, if you don’t specify a prefix it will use the https:// bucket URL by default. You can override this in config/asset_id.yml. For example if you wanted to use the https:// url:

production:
  access_key_id: 'MY_ACCESS_KEY'
  secret_access_key: 'MY_ACCESS_SECRET'
  bucket: "my_live_bucket"
  prefix: "https://my_bucket.s3.amazonaws.com"

To use Amazon CloudFront as a CDN for your assets all you need to do is create a CloudFront distribution for the bucket you have defined your configuration and then substitute your unique CloudFront domain name in config/environments/production.rb

config.action_controller.asset_host = Proc.new do |source|
 'https://my_domain.d374pjuyllr15e.cloudfront.net'
end

SSL works fine here as well.