How to get client ip from Google Network Load Balancer with kubernetes service

I created a kubernetes service in GKE with type:LoadBalancer.

apiVersion: v1
kind: Service
metadata:
  name: nginx
spec:
  type: LoadBalancer
  ports:
  - name: http
    port: 80
    targetPort: http
  selector:
    app: nginx

It's a nginx service and try to get origin client IP. like

        location / {
            echo $remote_addr;
            echo $http_x_forwarded_for;   
        }

But the result will get:

10.140.0.97

$remote_addr is like inside kubernetes IP.

$http_x_forwarded_for is empty.

I don't know why this is not like document said.

What I read

https://cloud.google.com/load-balancing/docs/network

Network Load Balancing is a pass-through load balancer, which means that your firewall rules must allow traffic from the client source IP addresses.

https://cloud.google.com/kubernetes-engine/docs/concepts/network-overview#ext-lb

If your Service needs to be reachable from outside the cluster and outside your VPC network, you can configure your Service as a LoadBalancer, by setting the Service's type field to LoadBalancer when defining the Service. GKE then provisions a Network Load Balancer in front of the Service. The Network Load Balancer is aware of all nodes in your cluster and configures your VPC network's firewall rules to allow connections to the Service from outside the VPC network, using the Service's external IP address. You can assign a static external IP address to the Service. Visit Configuring Domain Names with Static IP Addresses for more information.