Exactly, as it's pretty much standard with other CDN's, and has been for a very long time. Without any application level intelligence, you would end up with dup

Exactly, as it's pretty much standard with other CDN's, and has been for a very long time. Without any application level intelligence, you would end up with duplicate copies of content, as every node in every city ends up caching every bit of content. You're then limited to the amount of cache each node has, resulting in mush less available cache overall, more content expiring sooner, and even more requests back to the origin server. Although, if you use a tiered approach with some intermediate nodes between the end cachers and the origin server, you could mitigate this somewhat but it would still be quite suboptimal. The more standard method is to use a 2 layer approach, with the front end first layer intelligently hashing the full URL across the pool of the back end second layer. The trickier part then is if a single object requires more than one back end node, you need to be hash the same content to more than one node. This could be done by just having multiple pools of server on the back end, if the scale requires it.