I have the nginx upload module handling site uploads, but still need to transfer files (3-20 MB each, let's say) to our CDN, and would rather not delegate that to a background job. what is the best way to do this with Tornado without blocking other requests? Can I do this in an async callback?
Another name for "async callbacks" are background jobs. You've already got the right way to do it, why would you want suggestions on how to do it the wrong way?