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Difficulty: HardRoute 53 Routing Policies and DNS Failover Strategies

A company serves its global API through Amazon EC2 instances behind Application Load Balancers (ALBs) in the us-east-1 and eu-west-1 Regions. Currently, Route 53 is configured with latency-based routing to distribute traffic across these regions. The company wants to establish an active-passive disaster recovery (DR) plan. If the application endpoints in both primary regions fail their health checks, Route 53 must automatically redirect all user traffic to a static maintenance webpage hosted in an Amazon S3 bucket in us-west-2. The recovery time objective (RTO) is under 10 minutes. Which Route 53 routing configuration should a solutions architect implement to meet these requirements?

  1. A
    Configure latency-based alias records for the primary domain pointing directly to both ALBs. Create a failover routing policy with the primary domain as the primary record and the S3 static website endpoint as the secondary record, and set 'Evaluate Target Health' to No on the primary record to bypass health check propagation.
  2. B
    Configure latency-based CNAME records for the primary domain pointing to the ALBs in us-east-1 and eu-west-1. Create a third latency-based CNAME record pointing to the S3 static website endpoint and assign it a higher latency cost. Enable Route 53 health checks on all three CNAME records to trigger failover.
  3. Configure latency-based alias records for a subdomain pointing to the ALBs in us-east-1 and eu-west-1, with 'Evaluate Target Health' set to Yes on both. Create a primary failover alias record for the primary domain pointing to the subdomain with 'Evaluate Target Health' set to Yes, and a secondary failover alias record pointing to the S3 static website endpoint.Answer
  4. D
    Configure a primary failover alias record for the primary domain pointing to the latency-based subdomain with 'Evaluate Target Health' set to Yes. Create a secondary failover alias record pointing to the read replica endpoint of the application's Amazon RDS database in eu-west-1, allowing Route 53 to promote the replica to primary during failover.

Answer

The correct configuration is to use nested Route 53 records where latency-based alias records for a subdomain point to the ALBs with 'Evaluate Target Health' set to Yes, combined with primary and secondary failover records at the apex domain level that propagate health check status.
The correct configuration uses nested records to combine active-active latency routing with active-passive failover routing. By pointing the primary failover alias record to the latency-based alias records, and enabling 'Evaluate Target Health' on both the parent failover record and the child latency records, Route 53 monitors the health of the ALBs. If the ALBs in both regions fail their health checks, Route 53 detects that the primary failover target is unhealthy and redirects traffic to the secondary failover record pointing to the S3 static website.

Step-by-Step Solution

1
Identify the hybrid routing requirement.
The configuration requires active-active routing (latency-based) between the two active regions under normal operation, combined with active-passive failover to a static website on Amazon S3 during an outage.
This establishes the need for nested records because a single Route 53 record name cannot support both latency-based and failover routing policies simultaneously.
2
Design the active-passive failover record pair.
Create a primary failover alias record at the domain apex pointing to a nested subdomain, and create a secondary failover alias record pointing to the S3 static website endpoint.
This structures the DNS records so that traffic fails over to the backup S3 bucket only when the primary target group is deemed completely unhealthy.
3
Configure the nested active-active latency records with health check propagation.
Create latency-based alias records for the subdomain pointing to the respective regional ALBs, and enable 'Evaluate Target Health' on both the parent failover record and the child latency records.
Enabling 'Evaluate Target Health' on the child latency records ensures Route 53 monitors ALB health. Enabling it on the parent failover record ensures Route 53 checks the health of the subdomain targets and fails over to S3 if all underlying ALBs are unhealthy.

Key Concept

Route 53 active-passive failover can be configured over active-active latency-based routing by using nested alias records and enabling 'Evaluate Target Health' to propagate health status up the DNS record chain.
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Topics

Route 53 Routing Policies and DNS Failover Strategies

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