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Difficulty: MediumMulti-AZ, Multi-Region Architectures and Disaster Recovery (DR)

A telehealth platform hosts its patient portal application in the us-east-1 Region using Amazon EC2 instances and an Amazon RDS for MySQL DB instance. The company needs to design a pilot light disaster recovery (DR) strategy in the us-west-2 Region. The DR solution must achieve a Recovery Point Objective (RPO) of 15 minutes and a Recovery Time Objective (RTO) of 4 hours, while minimizing ongoing infrastructure costs. Which solution meets these requirements?

  1. A
    Deploy a warm standby environment in us-west-2 with a pre-configured Auto Scaling group running at minimum capacity. Set up an AWS Backup plan to copy RDS snapshots to us-west-2 every 12 hours.
  2. Configure an Amazon RDS cross-region read replica in the us-west-2 Region. Store the application tier as Amazon Machine Images (AMIs) in us-west-2, and launch the EC2 instances from the AMIs only during a failover event.Answer
  3. C
    Configure Amazon Route 53 latency routing to split database writes. Deploy a Multi-AZ RDS DB cluster in us-west-2 to automatically receive replicated database writes from the primary DB instance in us-east-1.
  4. D
    Configure Amazon S3 Cross-Region Replication (CRR) to copy database backup files from us-east-1 to an S3 Glacier Flexible Retrieval vault in us-west-2. Restore the database from S3 Glacier during a disaster.

Answer

Configure an Amazon RDS cross-region read replica in the us-west-2 Region. Store the application tier as Amazon Machine Images (AMIs) in us-west-2, and launch the EC2 instances from the AMIs only during a failover event.
The correct solution involves configuring an Amazon RDS cross-region read replica in us-west-2 to achieve low-latency asynchronous database replication. This satisfies the 15-minute RPO. By storing the application tier as AMIs in the secondary region and launching the EC2 instances only during a failover event, the solution minimizes ongoing compute costs while allowing the system to be fully provisioned well within the 4-hour RTO. This represents a classic pilot light disaster recovery strategy.

Step-by-Step Solution

1
Analyze RPO requirements.
To meet an RPO of 15 minutes, the database must replicate changes to the secondary region asynchronously with minimal lag. An RDS cross-region read replica provides this continuous, low-latency replication.
Traditional backup methods (like daily snapshots) would result in a recovery point of 12-24 hours, violating the 15-minute RPO constraint.
2
Analyze RTO and cost requirements.
To implement a cost-optimized 'pilot light' environment under a 4-hour RTO, application servers should not run continuously. Instead, keeping AMIs ready in the target region allows rapid deployment during a failover event.
Keeping EC2 instances powered down or unprovisioned minimizes compute costs, while launching them from AMIs takes under 30 minutes, easily fitting within the 4-hour RTO window.
3
Select the optimal disaster recovery configuration.
Combine the RDS cross-region read replica (for database RPO) with stored AMIs (for cost-efficient compute RTO).
This combination exactly satisfies the pilot light pattern: database replication is live (lighted), but compute resources are inactive until failover.

Key Concept

Disaster recovery (DR) strategies involve balancing RTO, RPO, and cost. A pilot light strategy maintains a running database replica to protect data (meeting strict RPOs) while keeping application compute resources idle or stored as AMIs to minimize costs.
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Topics

Multi-AZ, Multi-Region Architectures and Disaster Recovery (DR)

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