Heroku and Amazon CloudFront Cross-Origin Resources Sharing and Image URL

I have 1 question and 1 issue:

Question: If using CloudFront, is the image URL supposed to have s3.amazonaws.com or randomblah.cloudfront.net?

http://ift.tt/1DbYPUS

or with the actual cloudfront.net url...

http://ift.tt/1KAWS4i

Right now, I have this in my production.rb

config.action_controller.asset_host = 'fdawfwe8200.cloudfront.net'

Issue: I'm getting Redirect at origin 'http://ift.tt/1DbYPUU' has been blocked from loading by Cross-Origin Resource Sharing policy: No 'Access-Control-Allow-Origin' header.... error

How do I fix this?

The only thing I see breaking on my site is, bootstrap icons are boxes.