Origin Push CDNs A push CDN works very much like second server. User uploads content directly to the CDN for serving. Users can specify what content is uploaded, when it expires and when the content is updated. This method is also the most efficient in terms of how the traffic is used, content is uploaded only when it is new and when it is actually changed, thus keeping the amount of traffic in and out of your server to a minimum.
Origin Pull CDNs An origin pull CDN works very differently from a push one. With a pull CDN, the site owner simply leaves the content on their server and and rewrites their URLs to point to the CDN. When asked for a specific file, the CDN will first go to the the original server, “pull” the file off of it and serve it. The CDN will then cache that particular file and not query it again from the original server until it expires.