Use the header X-Forwarded-For - The X-Forwarded-For request header helps you identify the IP address of a client when you use an HTTP or HTTPS load balancer. Because load balancers intercept traffic between clients and servers, your server access logs contain only the IP address of the load balancer. To see the IP address of the client, use the X-Forwarded-For request header. Elastic Load Balancing stores the IP address of the client in the X-Forwarded-For request header and passes the header to your server.

Incorrect options:

You can get the Client IP addresses from server access logs - As discussed above, Load Balancers intercept traffic between clients and servers, so server access logs will contain only the IP address of the load balancer.

Use the header X-Forwarded-From - This is a made-up option and given as a distractor.

You can get the Client IP addresses from Elastic Load Balancing logs - Elastic Load Balancing logs requests sent to the load balancer, including requests that never made it to the targets. For example, if a client sends a malformed request, or there are no healthy targets to respond to the request, the request is still logged. So, this is not the right option if we wish to collect the IP addresses of the clients that have access to the instances.