AWS Certified Developer Associate (#2)

An application needs to use the IP address of the client in its processing. The application has been moved into AWS and has been placed behind an Application Load Balancer (ALB). However, all the client IP addresses now appear to be the same. The application must maintain the ability to scale horizontally. Based on this scenario, what is the MOST cost-effective solution to this problem?

Remove the application from the ALB. Delete the ALB and change Amazon Route 53 to direct traffic to the instance running the application.
Remove the application from the ALB. Create a Classic Load Balancer in its place. Direct traffic to the application using the HTTP protocol.
Alter the application code to inspect the
X-Forwarded-For
header. Ensure that the code can work properly if a list of IP addresses is passed in the header.
Alter the application code to inspect a custom header. Alter the client code to pass the IP address in the custom header.