How does a CDN work?

Question

Domain Name System

Tell me what underlies the work of CDNs that have servers in different countries. More specifically, I'm interested in the implementation of the next moment. For example, I buy several VPS located in different parts of the world, register a domain name like my-cool-cnd.net , upload the resources I need to the servers that I want the user to download from the server that is closer to him. But after all the domain name is casted in one ip!? And I want it to be cast to the ip of the server that is closer to the current user. Moreover, I would like to program this process manually. How it's done?

Answer 1

Well, actually, several ip-addresses can correspond to one DNS name ...
In general, options, right off the bat:
1. Who prevents the DNS server from responding with different ip-addresses based on the GeoIP data of the sender of the DNS request?
2. Why not start a "sorter" of requests, relying on the means of HTTP itself?
Let the user try to download some file my-cool-cnd.net/file. Then:
2.1. The HTTP server raised on my-cool-cnd.net sees through GeoIP that the user is in Europe and responds with HTTP code 307 Temporary Redirect, Location: europe.my-cool-cnd.net/file
What is important, on my -cool-cnd.net may not have any files at all - only a script redirector.
2.2. The user happily uploadseurope.my-cool-cnd.net/file
3. In general, a wild variant, which, nevertheless, is sometimes used: each regional CDN node announces the same ip-address over BGP. In this case, from which CDN node the download will go is decided by ip-routing, based on the principle of choosing the AS Path of the minimum length.