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Difficulty: MediumRoute 53 DNS Failover

A company uses Amazon Route 53 to manage DNS for its web application. The primary routing record is an Alias record pointing to an Application Load Balancer (ALB), and the secondary record is an Alias record pointing to an Amazon S3 static website bucket, configured as an active-passive failover pair. During a scheduled disaster recovery drill, all EC2 instances behind the ALB are stopped. However, external clients continue to be routed to the ALB, resulting in HTTP 503 Service Unavailable errors, rather than being redirected to the S3 bucket. Which configuration adjustment will resolve this issue and enable automatic failover?

  1. Configure the primary Alias record to evaluate target health.Answer
  2. B
    Reduce the Time to Live (TTL) of the primary Alias record to 10 seconds.
  3. C
    Associate a Route 53 health check with the secondary Alias record pointing to the S3 bucket.
  4. D
    Create a CloudWatch alarm based on ALB ActiveConnectionCount metrics to trigger the failover routing.

Answer

Configure the primary Alias record to evaluate target health.
The correct option is to configure the primary Alias record to evaluate target health. For Route 53 to automatically fail over when the backend targets of an Application Load Balancer (ALB) become unhealthy, the 'Evaluate Target Health' attribute must be set to 'Yes' on the primary Alias record. This setting enables Route 53 to query the load balancer's health checks to determine the status of the backend EC2 instances. If all instances are unhealthy, Route 53 marks the ALB as unhealthy and fails over to the backup S3 bucket.

Step-by-Step Solution

1
Analyze the active-passive failover configuration of Route 53.
The primary record points to an ALB, and the secondary record points to an S3 bucket.
Identify how Route 53 determines the health status of each endpoint.
2
Determine why Route 53 did not fail over when all EC2 instances behind the ALB were stopped.
Because Route 53 does not check the health of the ALB's target group by default unless explicitly configured to do so.
If 'Evaluate Target Health' is set to 'No', Route 53 assumes the load balancer is always healthy, regardless of the state of the back-end EC2 instances.
3
Select the correct option that enables backend health propagation to Route 53.
Enabling 'Evaluate Target Health' on the primary Alias record resolves the issue.
This configuration allows Route 53 to check the health of the registered EC2 instances and perform the failover when all instances are unhealthy.

Key Concept

Route 53 DNS Failover and Target Health Evaluation
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Topics

Route 53 DNS Failover

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