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

A real estate platform runs its production workload in the eu-west-1 Region. The architecture consists of Amazon EC2 instances in an Auto Scaling Group behind an Application Load Balancer, and an Amazon RDS for MySQL database. The company needs to design a disaster recovery (DR) strategy in the eu-central-1 Region with a Recovery Point Objective (RPO) of 15 minutes and a Recovery Time Objective (RTO) of 4 hours. Which strategy should a Solutions Architect recommend to meet these requirements with the lowest operational cost?

  1. A
    Deploy a warm standby architecture by running a scaled-down EC2 Auto Scaling Group and an active RDS Read Replica in the secondary region. Use Route 53 failover routing to automatically direct traffic. Promote the replica only if the primary region goes offline.
  2. Create an RDS Cross-Region Read Replica in the secondary region. Copy EC2 AMIs and launch templates to the secondary region, and configure an Auto Scaling Group with a desired capacity of 0. During a disaster, promote the replica to a standalone database, scale up the Auto Scaling Group, and update Route 53 DNS records.Answer
  3. C
    Enable multi-region multi-master replication on the RDS for MySQL database to allow simultaneous writes in both regions. Configure Route 53 latency routing to automatically fail over write traffic to the secondary region database instance without requiring database promotion.
  4. D
    Configure hourly database backups using AWS Backup and copy them to an Amazon S3 Glacier Flexible Retrieval vault in the secondary region. During failover, initiate standard retrieval of the backup to restore the database, and launch the EC2 instances from copied AMIs.

Answer

Create an RDS Cross-Region Read Replica in the secondary region, copy EC2 AMIs and launch templates, configure an Auto Scaling Group with a desired capacity of 0, and promote the database replica and scale up the Auto Scaling Group during failover.
The correct strategy uses an RDS Cross-Region Read Replica to continuously copy database changes, which meets the 15-minute RPO requirement. By maintaining the EC2 Auto Scaling Group at a capacity of 0 in the secondary region, the company avoids running compute instances during normal operations, minimizing costs. The replication promotion and Auto Scaling Group scaling processes can be completed well within the 4-hour RTO.

Step-by-Step Solution

1
Evaluate the recovery time objective (RTO) and recovery point objective (RPO) requirements.
RPO is 15 minutes, which requires active replication of data to the secondary region. RTO is 4 hours, which allows for some manual or scripted steps to provision resources during failover.
Determining the bounds of RPO and RTO guides the selection of the DR strategy (e.g., Pilot Light vs. Warm Standby vs. Backup and Restore).
2
Select the database replication method.
An RDS Cross-Region Read Replica provides asynchronous replication, ensuring replica lag is minimal (usually seconds or minutes) and meets the 15-minute RPO.
Standard backups copied to the secondary region or S3 Glacier cannot reliably guarantee a 15-minute RPO and would violate the RTO due to retrieval delays.
3
Design the compute replication strategy to minimize costs.
Store EC2 AMIs and launch templates in the secondary region, and configure an Auto Scaling Group with a desired capacity of 0. Scale it up only during failover.
Keeping EC2 instances at 0 capacity avoids ongoing compute charges, aligning with the constraint to minimize costs while easily launching instances within the 4-hour RTO window.

Key Concept

Selecting the most cost-effective disaster recovery strategy (such as Pilot Light) that satisfies recovery time (RTO) and recovery point (RPO) constraints using cross-region database replication and on-demand compute scaling.
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Topics

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

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