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Difficulty: HardRoute 53 Routing Policies and DNS Failover Strategies

A company hosts a critical web application on Amazon EC2 instances behind an Application Load Balancer (ALB) in the us-west-2 Region. The application queries a Multi-AZ Amazon RDS DB instance. The company wants to implement an active-passive disaster recovery (DR) strategy with a Recovery Time Objective (RTO) of under 2 minutes. The passive site consists of a static maintenance website hosted in an Amazon S3 bucket in the us-east-1 Region. The system must automatically redirect users to the maintenance page if the primary application servers or the database fail. Which configuration should a solutions architect implement to meet these requirements?

  1. Configure an HTTPS Route 53 health check to monitor a custom application endpoint that verifies database connectivity. Create a primary Failover Alias A record pointing to the ALB, associate it with the health check, and set Evaluate Target Health to Yes. Create a secondary Failover Alias A record pointing to the S3 static website endpoint.Answer
  2. B
    Configure a Route 53 Latency routing policy with Alias records pointing to both the ALB in us-west-2 and the S3 website endpoint in us-east-1. Enable Evaluate Target Health on both records so that Route 53 automatically redirects users to the S3 bucket if the ALB's latency increases due to a database outage.
  3. C
    Configure a primary Failover Alias record pointing to the ALB. For the database tier, create a Route 53 CNAME record pointing to the primary RDS database endpoint, and a secondary CNAME record pointing to an RDS Read Replica in us-east-1 with Evaluate Target Health enabled, expecting Route 53 to promote the read replica if the primary database fails.
  4. D
    Configure a primary Failover CNAME record pointing to the ALB's DNS name and enable Evaluate Target Health. In the secondary region, keep the backup web servers stopped to minimize running costs as a Pilot Light environment, and configure Route 53 to automatically start the EC2 instances during failover to meet the 2-minute RTO.

Answer

Configure an HTTPS Route 53 health check to monitor a custom application endpoint that verifies database connectivity. Create a primary Failover Alias A record pointing to the ALB, associate it with the health check, and set Evaluate Target Health to Yes. Create a secondary Failover Alias A record pointing to the S3 static website endpoint.
The correct configuration uses an HTTPS health check pointing to a custom endpoint on the application that actively verifies connection to the database. This deep health check ensures that database-level issues trigger a failover. By using an Alias A record for the primary ALB with Failover routing and Evaluate Target Health set to Yes, Route 53 can evaluate both the ALB health and the associated custom health check. Setting up the secondary Failover Alias record pointing to the S3 website endpoint ensures that Route 53 immediately routes traffic to the static maintenance page upon detecting primary failure, meeting the tight RTO requirement.

Step-by-Step Solution

1
Set up a deep health check endpoint on the web application.
An endpoint (such as /health) is created that checks connection to the Amazon RDS database and returns an HTTP 200 OK status only when the web servers and database are functional.
Standard ALB health checks only evaluate the ALB or the web servers, not downstream dependencies like the database. A deep health check ensures database failures trigger a failover.
2
Create a Route 53 health check.
A Route 53 HTTP/HTTPS health check is created pointing to the domain and the custom deep health endpoint, checking it at regular intervals.
This health check will report unhealthy if either the application servers or the database fails, providing the trigger for Route 53 to swap DNS targets.
3
Create the primary Route 53 Failover record.
An Alias A record pointing to the ALB is created with the Failover routing policy, associated with the Route 53 health check, and 'Evaluate Target Health' set to Yes.
Alias records allow the 'Evaluate Target Health' option to be set to Yes, which integrates the load balancer's health status with Route 53's routing decision.
4
Create the secondary Route 53 Failover record.
An Alias A record pointing to the S3 static website endpoint is created with the Failover routing policy.
When the primary record is determined to be unhealthy, Route 53 automatically fails over to the secondary record, pointing users to the maintenance page.

Key Concept

Active-passive DNS failover in Route 53 requires Alias records to support Evaluate Target Health, deep health checks to monitor backend dependencies, and a secondary resource that is immediately ready to serve traffic.
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Topics

Route 53 Routing Policies and DNS Failover Strategies

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