Exam AWS Certified Solutions Architect - Professional topic 1 question 74 discussion

D is incorrect - it passes the Client IP part of header, when proxy protocol is enabled. How will this improve availability. C will help ensure the load is distributed across instance in different AZs.

D. 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 load on two application servers in different Azs.

options C and D are the most suitable for your requirements, but the final choice between them depends on your specific needs and whether preserving the client's original IP address is essential for your application. If preserving the client's IP address is a priority, then option D is a good choice. Otherwise, option C with Cross-Zone Load Balancing is a simpler and effective approach for load balancing and high availability.

I would go for D as this is what was designed with protocol: add a header with the client information. Now with that information preserved the ELB can distribute and forward traffic anywhere. Having at least two machines in two AZ: if one fails you still have the second plus different availability zone even if the whole availability zone fails, the service will be up. Also future scalability is addressed: as long as we can preserve the header we can think of any load balancer or proxy ... to spread load. One thing: I do not understand the change request in C. Why would they need cross zone support in the application? From the question I only find that application needs the client IP and need to reach the database which is multi AZ. So why can't application can be deployed in multiple az without modification? I see no reason for such support.

"are currently taking that information from the TCP socket" and "During the migration you can change the application code" Before NLB is available, the choice is D. Now the better answer is C, no change of code, with client IP preserved (for target group type instance, or target group type IP with UDP_TCP listener)

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D. 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 load on two application servers in different Azs.

D. Proxy Protocol to obtain the clients IP address if the ELB is configured for TCP load balancing. X-Forwarded-For headers to obtain the clients IP address if the ELB is configured for HTTP(s) load balancing.