Put a load balancer between your reverse proxy and your backends. Problem solved.
What do you think nginx was being used for?
Re:Nginx to Be Acquired by F5 Networks
by brightball on Monday March 11, 2019 @11:13PM
(#19365065)
How’s Apache doing these days? Haven’t looked in a while
Nowhere near as fast with concurrent connections.
proxy_pass for example will only resolve a hostname at the time the configuration is parsed, unless you use a convoluted variable hack. This was a serious issue requiring you to restart your fleet if a backend server changed IPs. The bug fix for this was implemented only in Pro and sold as "DNS for Service Discovery."