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

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.

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.

- 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

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