You are migrating a legacy client-server application to AWS. The application responds to a specific DNS domain (e.g., www.example.com) and has a 2-tier architecture, with multiple application servers and a database server. Remote clients use TCP to connect to the application servers. The application servers need to know the clients` IP address to function properly and are currently taking that information from the TCP socket. A decision is made to use a multi-AZ RDS MySQL instance for the database. During the migration, you can change the application code. But you have to file a change request.

Answer options:

A.File a change request to implement Proxy Protocol Support in the application. Use an ELB with a TCP Listener and Proxy Protocol enabled to distribute the load on two application servers in different AZs.
B.File a change request to Implement Cross-Zone support in the application. Use an ELB with a TCP Listener and Cross-Zone Load Balancing enabled to distribute the load on two application servers in different AZs.
C.File a change request to implement Latency Based Routing support in the application. Use Route 53 with Latency Based Routing enabled to distribute the load on two application servers in different AZs.
D.File a change request to implement Alias Resource Support in the application. Use a Route 53 Alias Resource Record to distribute the load on two application servers in different AZs.

Answer – A
AWS ELB has support for Proxy Protocol. It simply depends on a humanly readable header with the client`s connection information to the TCP data sent to your server. As per the AWS documentation, the Proxy Protocol header helps you identify the IP address of a client when you have a load balancer that uses TCP for back-end connections. Because load balancers intercept traffic between clients and your instances, the access logs from your instance contain the load balancer`s IP address instead of the originating client. You can parse the first line of the request to retrieve your client`s IP address and the port number.
Option A is CORRECT because it implements the proxy protocol and uses ELB with a TCP listener. A change request is needed to support the proxy protocol in the application. With the proxy protocol in ELB, the backend servers can get the IP addresses of the clients.
Option B is incorrect because, although implementing cross-zone load balancing provides high availability, it states to use TCP forwarding, which does not support X-Forwarded-For.
Option C is incorrect because Route53 latency-based routing does not give the IP address of the clients.
Option D is incorrect because the Route53 Alias record does not give the IP address of the clients.
For more information on ELB enabling support for TCP, please refer to the links given below.
https://aws.amazon.com/blogs/aws/elastic-load-balancing-adds-support-for-proxy-protocol/
https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/enable-proxy-protocol.html