Disable cross-zone load balancing on the target group and initiate a zonal shift on the ALB
A company's web application uses an Application Load Balancer (ALB) to direct traffic to Amazon EC2 instances across three Availability Zones. The company has deployed a newer version of the application to one Availability Zone for testing. If a problem is detected with the application, the company wants to direct traffic away from the affected Availability Zone until the deployment has been rolled back. The application must remain available and maintain static stability during the rollback. Which solution will meet these requirements with the MOST operational efficiency?
Community Votes
100% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
The zonal shift capability has a documented prerequisite that cross-zone load balancing be disabled, and for an Application Load Balancer that attribute is configured on the target group, which is why option A disables it there rather than at the load balancer (A). Zonal shift then removes the whole Availability Zone from the load balancer's targets in a single, controlled action, which keeps the application available and does not change capacity elsewhere (A). Option B removes individual instances by hand, which drains only part of the zone and leaves the rest serving from the impaired zone. Option D removes the subnet, which removes the targets but does not perform a zonal shift and affects the zone more broadly than needed.
A newer version is running in one Availability Zone for testing and traffic must be taken away from that zone without disrupting the application or disturbing the remaining capacity. Route 53 Application Recovery Controller can shift traffic away from an impaired Availability Zone for an Application Load Balancer, but AWS documentation states the Elastic Load Balancing resources must have cross-zone load balancing turned off for the capability to work. For an Application Load Balancer that setting lives on the target group, so disabling cross-zone load balancing there and then initiating a zonal shift removes the affected zone from service while the other zones continue serving.
Manually removing instances in the target group that belong to the affected Availability Zone (B) — this deregisters instances one at a time so the remaining instances in the impaired zone continue receiving traffic, meaning the zone is not actually taken out of service and the application is not shielded from whatever made that zone unhealthy. Removing the subnet associated with the affected Availability Zone (D) — this removes the zone's targets but is not a zonal shift, and it is a broader infrastructure change than the controlled, reversible shift the requirement calls for while a rollback is pending. Leaving cross-zone load balancing enabled, as in C and D (C) — the documented prerequisite for zonal shift is not satisfied, so the shift cannot behave as required.
Community Discussion (3 comments)
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Expert Analysis
Why the Answer Is Correct
The requirement is to direct traffic away from one Availability Zone while keeping the application available and leaving the remaining capacity undisturbed. Amazon Route 53 Application Recovery Controller provides a zonal shift for an Application Load Balancer that temporarily removes an entire Availability Zone from service, and AWS documentation states that the Elastic Load Balancing resources must have cross-zone load balancing turned off for this capability to be used. For an Application Load Balancer, cross-zone load balancing is an attribute of its target groups rather than of the load balancer itself, so the correct prerequisite step is to disable cross-zone load balancing on the ALB's target group and then initiate the zonal shift on the ALB to direct traffic away from the affected Availability Zone (A). The shift is a single controlled action that leaves the healthy targets in the other zones serving, which satisfies the availability and stability requirements (A). A is the correct answer.Why the Other Options Are Wrong
B disables cross-zone load balancing on the ALB's target group and then manually removes instances in that target group that belong to the affected Availability Zone. While the cross-zone prerequisite is handled, deregistering instances individually only drains part of the zone: the remaining registered instances in that Availability Zone continue to receive traffic, so the zone is not actually removed from service and the application is not protected from the condition that made the zone unhealthy. The zonal shift capability exists precisely to take the whole zone out atomically. C configures cross-zone load balancing on the target group to inherit settings from the ALB and initiates a zonal shift. Leaving cross-zone load balancing enabled violates the documented prerequisite for the zonal shift capability, so the shift cannot operate as intended. D configures cross-zone load balancing to inherit from the ALB and removes the subnet associated with the affected Availability Zone. This is not a zonal shift; it is a broader infrastructure removal that takes the zone's targets out of service without the controlled, reversible zonal-shift semantics, and it does not satisfy the requirement's focus on shifting traffic while keeping the application stable during a rollback. A is correct.Community Comment Notes
Community voted A unanimously. Srikantha explained that Application Recovery Controller allows initiating a zonal shift to temporarily remove an entire Availability Zone, which provides quick and controlled traffic redirection. f4b18ba gave the reason cross-zone load balancing must be disabled, that doing so ensures each Availability Zone handles traffic only for its own targets, which is what allows traffic to be isolated away from the affected zone. matt200 confirmed A. No alternative received support.Official Reference
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