- [Narrator] On the screen here, you can see a diagram of exactly how CDN works. Let's put a little context behind it. In step one, User A requests a file or an asset via a URL with a special domain name. Such a domain name might be mydomain.azureedge.net. The domain name can actually be an endpoint hostname or even a custom domain. DNS then routes that request to the best performing point-of-presence, or PoP, which is often the point-of-presence that is geographically closest to the user requesting the content. 

Now, if there are no edge servers in the point-of-presence that have the requested file in their cache, the POP, or point-of-presence, requests the file from the originating server. The originating server could be an Azure Web App, an Azure Cloud Service, an Azure Storage Account, or essentially any other publicly accessible web server. Next, the originating server returns the requested file to one of the edge servers in the PoP. The edge server in the PoP then caches the file and returns it to the original requester, which is User A in this case. The file will then remain cached on that edge server in the PoP until the time to live, or TTL, that's specified by its HTTP headers, expires. The default TTL is seven days, unless the origin server provides a specific TTL. Other users can then request the same file by using the same URL that User A used, and can also be directed to the same PoP. If the TTL for the file hasn't expired, the PoP edge server returns the file directly from the cache instead of going back to the originating server. What this does is result in a far faster, more responsive end user experience.