AWS Certified Advanced Networking – Specialty (ANS-C01) — Question 200

A company has deployed an application in which the front end of the application communicates with the backend instances through a Network Load Balancer (NLB) in the same VPC. The application is highly available across two Availability Zones. The company wants to limit the amount of traffic that travels across the Availability Zones. Traffic from the front end of the application must stay in the same Availability Zone unless there is no healthy target in that Availability Zone behind the NLB. If there is no healthy target in the same Availability Zone, traffic must be sent to the other Availability Zone.

Which solution will meet these requirements?

Answer options

• A. Create a private hosted zone with weighted routing for each Availability Zone. Point the primary record to the local Availability Zone NLB DNS record. Point the secondary record to the Regional NLB DNS record. Configure the front end of the application to perform DNS lookups on the local private hosted zone records.
• B. Turn off cross-zone load balancing on the NLConfigure the front end of the application to perform DNS lookups on the local Availability Zone NLB DNS record.
• C. Create a private hosted zone. Create a failover record for each Availability Zone. For each failover record, point the primary record to the local Availability Zone NLB DNS record and point the secondary record to the Regional NLB DNS record. Configure the front end of the application to perform DNS lookups on the local private hosted zone records.
• D. Enable sticky sessions (session affinity) so that the NLB can bind a user’s session to targets in the same Availability Zone.

Correct answer: C

Explanation

Option C is correct because it ensures that traffic remains within the same Availability Zone while providing a fallback to the other zone if necessary through failover records. Option A uses weighted routing, which does not prioritize local targets effectively, while option B turns off cross-zone load balancing but doesn't address the requirement for DNS lookups. Option D focuses on session affinity, which does not control traffic routing based on target health in Availability Zones.