Origin pull CDN is a type of CDN where you don't have to upload files to the CDN server instead CDN does it for you. You only rewrite URLs to point to the CDN. When asked for a specific file, the CDN will first go to the original server, pull the file, cache and serve it.

Origin pull CDNs are easy to set up. However, it’s less flexible and can create redundant traffic as files are re-queried before they have been changed. Also it could be slow when files first loaded or browser tries access expired files.