AWS Certified CloudOps Engineer Associate SOA-C03 Practice Question

An application is deployed in two AWS Regions. Each Region has an identical stack of Amazon EC2 instances behind an Application Load Balancer (ALB). The public zone in Amazon Route 53 contains two A (alias) failover records that point to the Regional ALB DNS names. No health checks are associated with either record. During a complete outage in the primary Region (us-east-1), users still receive time-out errors instead of being routed to the secondary Region (us-west-2). Which configuration change will enable Route 53 to automatically direct traffic to the secondary Region when the primary ALB becomes unavailable?

Lower the TTL of both failover records to 0 seconds to force clients to re-query DNS more frequently.
Attach a CloudWatch alarm on the ALB's UnHealthyHostCount metric and associate that alarm with the primary record.
Enable cross-zone load balancing on both ALBs to allow Route 53 to fail over when one AZ goes down.
Edit the primary alias record and set Evaluate target health to Yes so Route 53 can monitor the ALB's status.

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Answer Description

For failover routing, Route 53 must be able to determine when the primary endpoint is unhealthy. When an alias record targets an ALB, Route 53 can automatically evaluate the load balancer's own health by enabling the Evaluate target health setting. If this flag is set to Yes on the primary failover record, Route 53 monitors the ALB's overall state; when the ALB becomes unhealthy (for example, all targets are unhealthy or the load balancer is unreachable), Route 53 stops returning that record and instead serves the secondary record. Creating an external health check, changing target group ports, or adjusting TTLs does not give Route 53 the information it needs to detect a Regional outage, and cross-zone load balancing affects traffic distribution inside a Region, not DNS failover across Regions.

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