How to bind a subdomain to another IP?

Question

Computer networks

There is a domain on reg.ru, there is a server on DigitalOcean, there is a client (domain owner).
For the client, a system has been developed that hangs on my server. How to create a subdomain that will knock on DigitalOcean, despite the fact that the client's main site (root domain) hangs on its server and cannot be transferred?

Answer 1

In the reg.ru control panel, if they have the same dns server

Answer 2

You need to add an A record to the DNS, where the full address of the site will be in the name field, and the address of your server will be in the IP field. Also immediately add a CNAME record like www.sub.domain.zone = sub.domain.zone