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

A Software-as-a-Service (SaaS) company hosts a document collaboration application in the us-east-1 Region. The application tier runs on Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer. User documents are stored in an Amazon S3 bucket, and metadata is stored in an Amazon Aurora MySQL-Compatible DB cluster. The company needs to implement a disaster recovery (DR) plan in the us-west-2 Region. The solution must achieve a Recovery Time Objective (RTO) of 4 hours and a Recovery Point Objective (RPO) of 15 minutes while minimizing ongoing infrastructure costs. Which solution meets these requirements most cost-effectively?

  1. Enable Amazon S3 Cross-Region Replication (CRR) to replicate document files to us-west-2. Create an Amazon Aurora Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2 with zero DB instances. Pre-configure the Application Load Balancer and the Auto Scaling group in us-west-2 with a desired capacity of zero. Configure Amazon Route 53 failover routing with health checks.Answer
  2. B
    Establish a warm standby environment in us-west-2 by maintaining a scaled-down Auto Scaling group with a minimum capacity of one EC2 instance and a running secondary Aurora DB instance. Use Amazon Route 53 latency routing to automatically redirect user sessions to the secondary region during a failover event.
  3. C
    Create hourly snapshots of the Aurora DB cluster and copy them to us-west-2. Store the application deployment templates in an S3 bucket configured to transition objects immediately to S3 Glacier Flexible Retrieval. Upon disaster declaration, retrieve the templates to deploy the infrastructure and restore the database from the copied snapshot.
  4. D
    Configure a cross-region Aurora Read Replica in us-west-2 to serve as the immediate database failover target. Deploy the EC2 application tier at full capacity in us-west-2 to ensure immediate availability. Use Amazon Route 53 simple routing to direct a portion of the write traffic to the read replica to keep it synchronized.

Answer

Enable Amazon S3 Cross-Region Replication (CRR) to replicate document files to us-west-2. Create an Amazon Aurora Global Database with the primary cluster in us-east-1 and a secondary cluster in us-west-2 with zero DB instances. Pre-configure the Application Load Balancer and the Auto Scaling group in us-west-2 with a desired capacity of zero. Configure Amazon Route 53 failover routing with health checks.
The correct solution represents a Pilot Light DR strategy, which is the most cost-effective way to meet a 4-hour RTO and 15-minute RPO. Amazon S3 Cross-Region Replication (CRR) and Amazon Aurora Global Database provide continuous, low-latency replication that satisfies the 15-minute RPO. Aurora Global Database supports having zero running DB instances in the secondary region cluster, and the EC2 Auto Scaling group can be configured with a capacity of zero. During a failover event, the DB instances are created, the Auto Scaling group is scaled up, and Route 53 failover routing directs traffic to the secondary region. This process completes well within the 4-hour RTO and incurs zero compute cost during normal operation.

Step-by-Step Solution

1
Determine the optimal disaster recovery pattern based on the RTO and RPO constraints.
An RTO of 4 hours suggests that a Pilot Light strategy is appropriate because compute resources (EC2 and Aurora DB instances) do not need to run continuously and can be provisioned or scaled up during failover.
This minimizes ongoing costs while easily meeting the generous 4-hour recovery window.
2
Choose replication mechanisms that satisfy the 15-minute RPO.
S3 Cross-Region Replication (CRR) and Aurora Global Database both replicate data continuously and asynchronously with sub-minute latency.
This ensures that data loss in the event of a disaster remains well under the 15-minute RPO limit.
3
Select the correct database and application configuration for Pilot Light.
Aurora Global Database allows the secondary DB cluster to have zero DB instances, eliminating compute costs. Similarly, pre-configured Auto Scaling groups can have their desired capacity set to zero.
This ensures zero compute expenses in the recovery region during normal operations, achieving the most cost-effective architecture.

Key Concept

Designing a Pilot Light disaster recovery strategy using S3 Cross-Region Replication and Aurora Global Database with zero-instance secondary clusters to meet recovery objectives cost-effectively.
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Topics

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

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