How to preserve the Client IP and pass it through ESP in Google Cloud Endpoints ESP Proxy?

Question

I have an application as an API using Google Cloud Endpoints which uses ESP as a proxy, my API application uses a service of type LoadBalancer. The App and the ESP proxy run inside the same pod, what I want is to preserve the client IP when they hit the ESP first and forward it to the API appliaction, I used the custom nginx config file here; https://cloud.google.com/endpoints/docs/openapi/custom-nginx and the forwarding didn't work, the application access log keeps showing remote address as 127.0.0.1:55922 which is the ESP proxy's ip not the remote client.

So what modification or config should I make to force ESP to forward the Clients IPs?