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Difficulty: HardRoute 53 DNS Failover

A company hosts a critical web application behind an Application Load Balancer (ALB) at the zone apex in the eu-west-1 (Ireland) Region. The SysOps administrator wants to configure an active-passive failover routing policy in Amazon Route 53 to redirect user traffic to a static maintenance page hosted on an Amazon S3 bucket website endpoint in the us-west-2 (Oregon) Region. The failover must trigger if the HTTP 5xx error rate of the application exceeds a specific threshold (monitored by a CloudWatch alarm) or if the ALB target group becomes entirely unhealthy. The administrator wants to ensure that DNS failover occurs with minimal delay when a failure is detected.

Which combination of actions should the SysOps administrator take to meet these requirements? (Select TWO.)

  1. Create a CloudWatch alarm in the us-east-1 Region to monitor the application's 5xx error rate metric in eu-west-1 using detailed monitoring (1-minute intervals), and configure a Route 53 health check that monitors this alarm.Answer
  2. Create a primary failover Alias A record at the zone apex pointing to the ALB, associate the record with the CloudWatch-alarm-based Route 53 health check, and set Evaluate Target Health to Yes.Answer
  3. C
    Create a CloudWatch alarm in the eu-west-1 Region to monitor the application's 5xx error rate metric using standard monitoring (5-minute intervals), and configure the Route 53 health check to monitor this alarm directly.
  4. D
    Create a primary failover CNAME record at the zone apex pointing to the ALB DNS name, set its TTL to 300 seconds, and associate the record with the Route 53 health check.
  5. E
    Create a secondary failover Alias A record at the zone apex pointing to an Amazon RDS Read Replica endpoint in us-west-2 to act as the primary database failover target.

Answer

Create a CloudWatch alarm in the us-east-1 Region using detailed monitoring to track the HTTP 5xx error rate metric and create a Route 53 health check to monitor it. Additionally, create a primary failover Alias A record at the zone apex pointing to the ALB with Evaluate Target Health set to Yes and associate it with the Route 53 health check.
To set up active-passive failover based on custom metrics with minimal delay, a CloudWatch-alarm-based Route 53 health check is required. The alarm must be created in the us-east-1 Region (even though the application is in eu-west-1) and configured with detailed monitoring (1-minute intervals) to ensure quick response times. At the zone apex, a CNAME cannot be used, so a primary failover Alias A record pointing to the ALB is required. Associating the record with the Route 53 health check and enabling Evaluate Target Health ensures failover occurs if either the application health checks fail or the error-rate alarm triggers.

Step-by-Step Solution

1
Configure a CloudWatch alarm in the us-east-1 Region monitoring the HTTP 5xx metric of the ALB located in the eu-west-1 Region, ensuring detailed monitoring (1-minute intervals) is enabled for fast detection.
The metric alarm is active in the required us-east-1 Region.
Route 53 health checks can only monitor CloudWatch alarms that are created in the us-east-1 Region.
2
Create a Route 53 health check of type 'State of CloudWatch alarm' pointing to the newly created alarm in us-east-1.
The Route 53 health check changes to unhealthy when the CloudWatch alarm is triggered.
This links the application-level degradation metric to Route 53's failover logic.
3
Create a primary failover Alias A record at the zone apex pointing to the ALB. Associate the Route 53 health check with this record and enable 'Evaluate Target Health'.
Route 53 evaluates the health of the ALB targets and the CloudWatch alarm health check.
If either the target group fails or the 5xx error rate alarm is triggered, the record is marked unhealthy, triggering failover. An Alias record must be used because CNAMEs cannot be placed at the zone apex.

Key Concept

Route 53 active-passive DNS failover using Alias records, Evaluate Target Health, and cross-region CloudWatch alarm integrations.
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Topics

Route 53 DNS Failover

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