Hi @JrmyDev ,
Not it’s not supported and generally not a good practice because of all the reverse DNS lookups Nginx will have to make on each incoming request, leading to more latency before answering the very first request, Nginx internal caching to manage, more load on Nginx in case of several incoming requests and a very simple way to be DDOS.
Nginx has a module for it, but as you can see not well supported GitHub - flant/nginx-http-rdns: Nginx HTTP rDNS module.
Another solution, in this case, is to add authentication instead of whitelisting IPs. I don’t know if your app can do so, would it be an acceptable solution in your case?
Pierre