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Zorluk: Çok zorAuto Scaling and Elastic Load Balancing (ELB)

A multinational financial services firm hosts a critical transactional API across two AWS Regions: us-east-1 (primary) and us-west-2 (disaster recovery). In both regions, the API runs on Amazon EC2 instances managed by an Auto Scaling group (ASG) behind an Application Load Balancer (ALB) and is configured to listen on custom TCP port 8443. The firm uses Amazon Route 53 with failover routing policies pointing to the ALBs via Alias records. During a simulated failover drill, the API service on the EC2 instances in us-east-1 is stopped, causing the instances to become unhealthy. However, Route 53 does not route traffic to the us-west-2 ALB, and external clients continue to receive timeout errors from us-east-1. Which configuration changes must the solutions architect implement to resolve this issue and enable automated failover?

  1. Enable Evaluate Target Health on the Route 53 primary Alias record, and configure the ALB target group health check to query the custom application port 8443.Cevap
  2. B
    Change the Route 53 routing policy to Latency-based routing for both regions, and configure the ALBs to automatically redirect client traffic to the next closest region when latency spikes.
  3. C
    Modify the ALB target group health check port to port 80, configure a basic web server on the EC2 instances to respond to port 80 health checks, and rely on the default Route 53 health checking behavior.
  4. D
    Update the primary subnet Network ACL to allow inbound traffic from the Route 53 health checker IP addresses on port 8443, and configure the EC2 security group to trust Route 53 public IP ranges.

Cevap

Enable Evaluate Target Health on the Route 53 primary Alias record, and configure the ALB target group health check to query the custom application port 8443.
The correct option is to enable Evaluate Target Health on the primary Route 53 Alias record and ensure the target group health check monitors port 8443. For an ALB Alias record, Route 53 determines health by evaluating the target group's health metrics. If 'Evaluate Target Health' is set to Yes and the target group correctly monitors the custom API port, the failure of the API service will cause all targets to become unhealthy, which in turn causes Route 53 to failover to the disaster recovery region.

Adım Adım Çözüm

1
Analyze Route 53 Alias health evaluation behavior.
By default, Route 53 Alias records do not evaluate the health of the underlying resources (the ALB's targets) unless the 'Evaluate Target Health' parameter is explicitly set to Yes.
This is necessary because Route 53 needs permission and instructions to inspect the health of the ALB target group.
2
Examine the target group health check configuration.
The target group must query the port where the actual application is listening (port 8443) rather than a default port (like port 80).
If the health check port is misconfigured, the ALB may continue to report the instances as healthy even when the core API application has crashed or stopped.
3
Synthesize the requirements for automatic DNS failover.
Combining 'Evaluate Target Health' on the Alias record with a correct health check port configuration allows Route 53 to detect that zero healthy targets exist in the primary region's ALB target group, triggering an automatic failover to the secondary region.
Route 53 marks an ALB as unhealthy only when all targets in all associated target groups are unhealthy.

Anahtar Kavram

Route 53 DNS failover relies on the combination of Alias record health evaluation and accurate Application Load Balancer target group health checks.
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Auto Scaling and Elastic Load Balancing (ELB)

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