Disable cross-zone load balancing on the target group and start an Application Recovery Controller zonal shift

DOP-C02 By islever Editorial Last updated

Implement automated recovery processes to meet RTO and RPO requirements. Implement highly available solutions to meet resilience and business requirements.

Short answer

B Disable cross-zone load balancing on the ALB's target group, then start an Application Recovery Controller zonal shift.

Question

A company has an application that runs on Amazon EC2 instances behind an Application Load Balancer (ALB). The EC2 instances are in multiple Availability Zones. The application was misconfigured in a single Availability Zone, which caused a partial outage of the application. A DevOps engineer made changes to ensure that the unhealthy EC2 instances in one Availability Zone do not affect the healthy EC2 instances in the other Availability Zones. The DevOps engineer needs to test the application's failover and shift where the ALB sends traffic. During failover, the ALB must avoid sending traffic to the Availability Zone where the failure has occurred. Which solution will meet these requirements?
  1. Turn off cross-zone load balancing on the ALB. Use Amazon Route 53 Application Recovery Controller to start a zonal shift away from the Availability Zone.
  2. Turn off cross-zone load balancing on the ALB’s target group. Use Amazon Route 53 Application Recovery Controller to start a zonal shift away from the Availability Zone. Correct Answer
  3. Create an Amazon Route 53 Application Recovery Controller resource set that uses the DNS hostname of the ALB. Start a zonal shift for the resource set away from the Availability Zone.
  4. Create an Amazon Route 53 Application Recovery Controller resource set that uses the ARN of the ALB’s target group. Create a readiness check that uses the ElbV2TargetGroupsCanServeTraffic rule.

Key Takeaways

The zonal shift capability requires cross-zone load balancing to be disabled, and for an Application Load Balancer that setting lives on the target group, not on the load balancer (B). Option A tries to turn it off on the ALB, which the ALB documentation does not support, so the prerequisite would never be satisfied. Option C creates the resource set from the ALB's DNS hostname, but the shift cannot actually take effect while cross-zone load balancing remains enabled. Option D uses the target group ARN with an ElbV2TargetGroupsCanServeTraffic readiness check for automatic detection, which automates verification rather than shifting traffic away from the failed zone as the requirement states.

Route 53 Application Recovery Controller can shift traffic away from a failed Availability Zone for an Application Load Balancer, but AWS documentation states that the Elastic Load Balancing resources must have cross-zone load balancing turned off for this capability to work. Cross-zone load balancing on an Application Load Balancer is disabled through the attribute on its target group, not on the load balancer itself. With cross-zone load balancing off at the target group level, a zonal shift can move routing away from the impaired zone and the healthy targets in the other zones continue to serve traffic.

Common mistake: Turning off cross-zone load balancing on the ALB itself (A) — CHRIS12722222 and spring21 both noted this cannot be done at the ALB level; it is a target group attribute, making B the correct choice. Using a resource set created from the ALB's DNS hostname (C) — even with a valid resource set, zonal shift requires cross-zone load balancing to be disabled, which option C never does. Creating a resource set from the target group ARN with an ElbV2TargetGroupsCanServeTraffic readiness check (D) — the readiness check is an automatic application recovery verification mechanism, not a mechanism for shifting traffic away from an impaired Availability Zone.

Expert Analysis

Why the Answer Is Correct

Amazon Route 53 Application Recovery Controller supports zonal shifts for Application Load Balancers so that traffic can be moved away from an impaired Availability Zone, and AWS documentation states that the Elastic Load Balancing resources must have cross-zone load balancing turned off to use this capability. For an Application Load Balancer, cross-zone load balancing is an attribute of its target groups rather than of the load balancer, so the correct configuration step is to turn it off on the ALB's target group (B). With that prerequisite satisfied, starting a zonal shift away from the failed Availability Zone causes the load balancer to stop sending traffic there while the healthy targets in the other zones continue to serve, which is exactly the failover behavior and traffic shift the requirement describes.

Why the Other Options Are Wrong

A instructs turning off cross-zone load balancing on the Application Load Balancer. As spring21 and CHRIS12722222 observed, this setting cannot be changed at the ALB level for an Application Load Balancer; it must be disabled through the target group settings, so this step would not achieve the prerequisite. C creates an Application Recovery Controller resource set from the ALB's DNS hostname and starts a zonal shift, but it never disables cross-zone load balancing, so the documented prerequisite for the capability is unmet and the shift cannot behave as required. D creates a resource set from the target group ARN with an ElbV2TargetGroupsCanServeTraffic readiness check; that readiness check is the mechanism for automatically verifying application recovery readiness, not for initiating a zonal shift away from a failed zone, so it does not meet the requirement to shift where the ALB sends traffic. B is the correct answer.

Community Comment Notes

Community was split, A (52) versus B (39). inturist supported A citing the zonal shift documentation's note about cross-zone load balancing, but CHRIS12722222 and Shenannigan both cited the ALB documentation showing cross-zone load balancing is disabled through the target group for an Application Load Balancer, making B correct. The documentation basis for B is the more specific and verifiable of the two.

Official Reference

These links open the official vendor documentation in a new tab.

Community Votes

A
57%
B
43%

57% of anonymous learners picked answer A. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 9 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 9

  1. inturist 👍 6 Answered A
    For me the correct answer is A:"Note that the Elastic Load Balancing resources must have cross-zone load balancing turned off to use this capability." https://docs.aws.amazon.com/r53recovery/latest/dg/arc-zonal-shift.html
  2. Shenannigan 👍 4 Answered B
    Answer is B You can not turn of cross-zone load balancing on an ALB: https://docs.aws.amazon.com/elasticloadbalancing/latest/application/application-load-balancers.html#cross-zone-load-balancing You can turn it off at the Target Group: https://aws.amazon.com/about-aws/whats-new/2022/11/application-load-balancers-turning-off-cross-zone-load-balancing-per-target-group/ zonal shift: https://docs.aws.amazon.com/elasticloadbalancing/latest/userguide/how-elastic-load-balancing-works.html#cross-zone-load-balancing#:~:text=zonal%20shift
  3. jamesf 👍 3 Answered A
    - Turning off cross-zone load balancing on the ALB ensures that each Availability Zone only handles traffic directed to its own healthy instances, allowing for granular control over traffic distribution. This prevents the ALB from sending traffic to the unhealthy instances across all zones, thereby isolating the problem to the affected zone. - Amazon Route 53 Application Recovery Controller's Zonal Shifts is used to direct traffic away from a specific AZ that experiences a failure, allowing the ALB to reroute requests to healthy AZs automatically. Amazon Route 53 Application Recovery Controller currently supports the following resources for zonal shift and zonal autoshift: - Network Load Balancers with cross-zone load balancing disabled - Application Load Balancers with cross-zone load balancing disabled https://docs.aws.amazon.com/r53recovery/latest/dg/arc-zonal-shift.resource-types.html
  4. limelight04 👍 2 Answered A
    A is the most appropriate answer due to the reasons below; Option A: Turning off cross-zone load balancing on the ALB and using Amazon Route 53 Application Recovery Controller to start a zonal shift away from the affected Availability Zone ensures that traffic is not sent to the unhealthy instances in the problematic zone. This directly addresses the need to avoid sending traffic to the Availability Zone where the failure has occurred. Option D: While creating a resource set and readiness check with Amazon Route 53 Application Recovery Controller is useful for monitoring and ensuring traffic is routed to healthy instances, it doesn’t explicitly mention turning off cross-zone load balancing, which is crucial for isolating the affected Availability Zone.
  5. trungtd 👍 2 Answered C
    A&B Turn off cross-zone load balancing is a bad idea D involves creating a readiness check rule (ElbV2TargetGroupsCanServeTraffic) which checks the ability of the ALB’s target groups to serve traffic. However, this does not directly control traffic routing based on Availability Zone health. C Route 53 Application Recovery Controller: It directly manages traffic based on health checks and allows for zonal shifts Zonal Shift: Specifically addresses the requirement to avoid sending traffic to an Availability Zone experiencing issues
Show 4 more comments
  1. spring21 👍 2 Answered B
    To turn off cross-zone load balancing on an Application Load Balancer (ALB), you cannot directly disable it at the ALB level; instead, you need to modify the target group settings and explicitly disable cross-zone load balancing within the target group attributes
  2. CHRIS12722222 👍 2 Answered B
    Cant turn off cross zone load balancing at ALB level
  3. chinchin97 👍 1 Answered B
    Turning off cross-zone load balancing at the target group level ensures that each target group handles traffic independently for its specific Availability Zone. Why specifically target group is because cross-zone load balancing is always turned on and cannot be turned off for a ALB. But, if using target group, the default is to use the load balancer setting, which you can override the default by explicitly turning cross-zone load balancing off at the target group level. The next part us to move away from the affected region by using Amazon Route 53 Application Recovery Controller. Option A works well for a ELB, but for ALB, you can't turn off cross-zone load balancing. Option C is good to handle DNS failover, but doesn't stop traffic from going to the affected zone. Option D doesn't handle moving of traffic away from the affected zone and add extra complexity by introducing a readiness check.
  4. jojewi8143 👍 1 Answered A
    i choose a

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