What will advise means (it is possible paid) for DNS balancing (DNS is available only through VPN) between two DPCs?

Question

Domain Name System

Given:
1) 2 data centers, in each data center via a VPN gateway.
2) Many users who permanently have access to both data centers via VPN.
3) Each data center has a DNS server, which is a tunneled resource for users.
4) Users must receive a web resource through a VPN, while balancing is planned using DNS.
5) DNS requests from end hosts go only through the VPN, requests to the DNS provider are blocked by the firewall.
How to make DNS servers issue addresses based on the availability and workload of two data centers.

Answer 1

Balancing with DNS - https://ru.wikipedia.org/wiki/Round_robin_DNS
but this method has the disadvantage of caching DNS records. In an ideal world, this is done through haproxy or nginx upstream fails.

Answer 2

In order to balance taking into account the load of the data center, you must first measure and collect this load with something, then the DNS server must, based on this data, give the desired IP. I did not see ready-made solutions (I did not look for them). I agree with nikolayvaganov , balancing the application itself is better for these purposes, but I don’t know how to implement this in your environment. As an option, you need another location where there will be a balancer that will scatter traffic to different data centers.