Parked in front of an nginx instance that serves all of our static assets. Performance and reliability have been excellent, and the header pass-through rules are wonderful. Price is affordable, as well.
We chose CloudFront mostly because it’s incredibly popular. But also because it’s the recommended CDN for Heroku, which means there shouldn’t be any problems using them together. Rails makes it really easy to drop in a CDN reference for your app so that when your assets get compiled, they’re shipped off to the CDN and then deployed with your app.
So anytime we push to Heroku, we’re pushing up to CloudFront (if the assets don’t already exist). One major issue we still haven’t been able to solve involves Fonts. Has anyone actually been able to get fonts served up through CloudFront using Rails 4 and Heroku? Literally spent hours researching this and can’t find any solutions. We ended up just referencing a CDN for all the font libraries.
We have a separate distribution for each environment, since I don’t think it’s possible to use the same distribution for the multiple domains.