transfer data between main server and child server

I have decided to create a child server that is connected to the mother server through VPN to solve the problem of slow speed and necessary stability.
I also want the information to be uploaded to the child server as a cache …
Anyway, the amount of information transfer is very high and compared to the large amount of information, I would be grateful if you could give me a suitable solution in this field.

It would be interesting to know how you did this? If they were identical servers, you would also have to keep the database synchronised, for example. Do you do that?

It would probably be better if you solved the first problem. Tell us more about your main server, server connection, route from the clients to the server, cloud or on prem, server equipment, etc. There are many companies that, although they certainly have a much larger Nextcloud infrastructure, do not try to synchronise between Nextclouds in any way. But perhaps they invest more money in the network connection and the equipment of the main Nextcloud server.

An insiders look into scaling Nextcloud - Matthias Wobben