A company has a set of EC2 Instances placed behind an Elastic Load Balancer. There is a requirement from the IT Security department to get a list of the client’s IP addresses which establishes a connection with the load balancer. Which of the following can help with this requirement?

Answer options:

A.Use CloudTrail logs
B.Use CloudWatch metrics for the ELB
C.Enable Access logs for the ELB
D.Use the AWS Config service

Correct Answer: C
The AWS Documentation mentions the following.
Elastic Load Balancing provides access logs that capture detailed information about requests sent to your load balancer. Each log contains information such as the time the request was received, the client`s IP address, latencies, request paths, and server responses. You can use these access logs to analyze traffic patterns and troubleshoot issues.
Access logging is an optional feature of Elastic Load Balancing that is disabled by default. After you enable access logging for your load balancer, Elastic Load Balancing captures the logs and stores them in the Amazon S3 bucket that you specify as compressed files. You can disable access logging at any time.
Option A is incorrect since CloudTrail captures all API calls for Elastic Load Balancing as events. The calls captured include calls from the AWS Management Console and code calls to the Elastic Load Balancing API operations.
Option B is incorrect since the CloudWatch metrics will not provide the required data. Elastic Load Balancing publishes data points to Amazon CloudWatch for the load balancers and the targets. 
Option D is incorrect since AWS Config is a service that enables you to assess, audit, and evaluate the configurations of your AWS resources. 
For more information on the Classic Load Balancer, please visit the below URL-
https://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-access-logs.html
https://aws.amazon.com/config/