Use multiple Heroku apps to load balance Nginx

I need to create one system that requires:

• 1 Node.js Server is used for reverse proxy for load balancing with Nginx.

• 4 Node.js Server is used for RESTful APIs. They all need to be connected to the server above.

I found out there is no solution to point out in case of using multiple heroku load balancing apps . How should I configure the file nginx.conf.erb

on the first server to connect the 4 Heroku servers correctly? I am trying to implement this link http://nginx.org/en/docs/http/load_balancing.html but I only get it 400 base request

.