ruby on rails - Paperclip is not generating url properly for CNAME -

i'm tying cloudfront distribution wired custom domain paperclip it's not generating url properly. here configuration:

# initializers/paperclip_defaults.rb paperclip::attachment.default_options.merge!({   :storage => :s3,   :s3_credentials => "#{rails.root}/config/amazon_s3.yml",   :bucket => "my-image-bucket",   :path => "production/attachments/:attachment/:id/:style/:basename.:extension",   :url => ":s3_host_alias",   :s3_headers => {'cache-control' => 'max-age=2147483648'},   :s3_protocol => :https,   :s3_host_alias => "cdn.mydomain.com", }) 

according docs , every blog post i've read should correct. problem winds generating this:

https://s3.amazonaws.com/my-image-bucket/production/products/images/44/original/my-image.jpg

the way i've gotten use cname specifying s3_host_name according documentation used tokyo region. , breaks uploads. ideas i'm doing wrong?

i'm using paperclip 3.5.2.

update

i'm debugging inside attachment.rb#url , here's i'm seeing. paperclip::attachment.default_options[:url] returns cdn.mydomain.com correct. however, @options[:url] returning :s3_path_url instead of s3_host_alias. reason default option not being merged in properly. s3_host_alias option since @options[:s3_host_alias] returning cdn.mydomain.com expected.

so turns out :s3_alias_url correct token use url , not :s3_host_alias. not sure that's documented though. had @ s3.rb figure out.