I appreciate your constant support very much @crypto.piotr :)
That is indeed fascinating.
You are right. I haven't even been aware of CDNs existence before preparing this post.
Would you mind telling me how do those servers synchronize content?
Really interesting question. I generally suppose that CDN servers don't need to synchronize content very fluently and quickly. The most extreme situation I can imagine that demands a lot of content syncing is a real time gaming. However, even in this case players are usually divided between particular CDNs according to their location, so I think that synchronization between them doesn't need to be very fast.
However, they certainly do it sometimes. This process is called replication and means that each server sends new data to the main server (for example statistics of players in a particular real-time game). Then, the main server creates some unified version of whole content and sends 'actualization' back to the servers.
This comment is based on my own assumptions and some quick research, so I am not sure if it is accurate ;)
Dziekuje @neavvy :)