I’ve fundamental nginx load-balancing setup in place, e.g.

http {
  ... ## some stuff, log codecs, and so on.
  upstream backend {
    server localhost:8001
    server localhost:8002
  }
  server {
    hear 80 default_server;
    server_name foo.com;
    location / {
      proxy_pass http://backend/foo/bar/;
    }
  }
}

However I might prefer to parameterize the proxy_pass URL with a price/variable that is particular to the chosen upstream server. For instance, if the server with port 8001 is chosen, I might like to make use of proxy_pass http://backend/foo/bar/8001, and likewise if the server with port 8002 is chosen, I might like to make use of proxy_pass http://backend/foo/bar/8002 (the place backend is clearly changed by the chosen server identify, as per nginx’s traditional load-balancing setup).

Does anybody know if that is doable?

(I do know I might do some self-routing inside nginx to realize this … e.g. organising two new nginx addresses which might be the upstreams, then proxy_pass every a kind of individually, however I am questioning if there is a method to dynamically rewrite the URL handed to the upstream server after the subsequent upstream server to strive has been chosen by the load-balancing system.)