How to find the nearest server to the client?

Question

Computer networks

There is a site that gives files for download, but now there is not enough channel or capacity, we want to distribute the load and give files from other servers, but also ours. How can we determine the best server for the client?
PS: CDN is not suitable, you need to give it from our servers.

Answer 1

Then you need to build your CDN. And how to organize it was written many times. It is very difficult, expensive and with a huge number of problems.
Why isn't a CDN right for you?

Answer 2

1) collect all the IP addresses of incoming clients from the logs
2) group them by operators (by BGP AS numbers) and by the number of requests
3) buy hosting as close as possible to these operators (ideally - the hosting provider is the same as in the first list positions in step 2)
4) sort everything heavy into hostings, and when the client opens the page, generate the name of the servers based on which hosting is closer to it (such as dc01.example.com)
5) unbalance DNS by country
6) if not enough, build your infrastructure aka CDN with blackjack and... you get the idea