I think I get it.
In config / initializers / paperclip_defaults.rb
Paperclip::Attachment.default_options.update({ :path => "images/:class/:id/:attachment/:style/img_:fingerprint", :storage => :fog, :fog_credentials => { :provider => 'Rackspace', :rackspace_username => 'blablabla', :rackspace_api_key => 'blablabla', :persistent => false }, :fog_directory => 'blablabla', :fog_public => true, :fog_host => 'http://blablabla.rackcdn.com' })
Where...
: fog_directory . This is your Rackspace cloud storage container.
: fog_host - CDN URL of the cloud file
: permanent . To prevent an error in Fog / Excon. You may not need this in the future.
Also use the : fingerprint clip function to avoid caching CDN when updating a file.
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