Q40 — AWS DOP-C02 Ch.3
Question 40 of 100 | ← Chapter 3
A company’s web application uses an Application Load Balancer (ALB) to distribute traffic across Amazon EC2 instances in three Availability Zones. The company has deployed a new version of the application to one Availability Zone for testing. If issues are discovered, the company wants to redirect traffic away from the affected Availability Zone back to the previously deployed version before rollback. During the rollback process, the application must remain available and maintain state stability.
- A. Disable cross-zone load balancing on the ALB target group. Initiate zone draining on the ALB to divert traffic away from the affected Availability Zone. ✓
- B. Disable cross-zone load balancing on the ALB target group. Manually deregister instances in the affected Availability Zone from the target group.
- C. Configure cross-zone load balancing on the ALB target group to inherit settings from the ALB. Initiate zone draining on the ALB to divert traffic away from the affected Availability Zone.
- D. Configure cross-zone load balancing on the ALB target group to inherit settings from the ALB. Delete the subnet associated with the affected Availability Zone.
Correct Answer: A. Disable cross-zone load balancing on the ALB target group. Initiate zone draining on the ALB to divert traffic away from the affected Availability Zone.
Explanation
The core requirement is rapidly isolating a problematic Availability Zone while maintaining service availability. Application Load Balancer (ALB) cross-zone load balancing distributes traffic evenly across all Availability Zones’ instances; disabling it ensures traffic is distributed only according to each zone’s capacity. When a specific Availability Zone fails, disabling cross-zone load balancing (to prevent automatic traffic compensation to other zones) and initiating zone draining (actively stopping traffic routing to the problem zone) achieves static, stable rollback without deleting instances or subnets, avoiding service disruption. Option A precisely controls traffic routing through these two steps, adhering to the principle of minimal change.