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

A smart home IoT monitoring service hosts its primary application in the us-east-1 Region. The architecture consists of Amazon EC2 instances in an Auto Scaling group behind an Application Load Balancer, an Amazon RDS for PostgreSQL database, and static configuration files stored in an Amazon S3 bucket.

The company needs to establish a disaster recovery (DR) site in the us-west-2 Region. The DR solution must achieve a Recovery Time Objective (RTO) of 2 hours and a Recovery Point Objective (RPO) of 15 minutes, while minimizing ongoing infrastructure costs.

Which combination of actions should the solutions architect take to meet these requirements? (Select TWO.)

  1. Set up an Amazon RDS cross-region read replica in the secondary region, and configure Amazon S3 Cross-Region Replication (CRR) to copy static files to the secondary region.Answer
  2. Deploy an Application Load Balancer and configure an Auto Scaling group with the desired capacity set to zero in the secondary region, and ensure application Amazon Machine Images (AMIs) are pre-copied to the secondary region.Answer
  3. C
    Configure Amazon RDS Multi-AZ replication to synchronize database writes between the primary and secondary regions for automatic failover.
  4. D
    Store the static files in Amazon S3 Glacier Flexible Retrieval in the secondary region and configure standard retrieval to recover data during a failover event.
  5. E
    Deploy a duplicate EC2 Auto Scaling group and Application Load Balancer running at full production capacity in the secondary region to maintain a hot standby.

Answer

Setting up an Amazon RDS cross-region read replica and Amazon S3 Cross-Region Replication (CRR) ensures data is replicated asynchronously to meet the 15-minute RPO. Pre-configuring the Application Load Balancer and an Auto Scaling group with zero capacity in the secondary region establishes a Pilot Light strategy that minimizes baseline cost while allowing full scaling within the 2-hour RTO.
The correct combination of actions uses a Pilot Light disaster recovery strategy to achieve the RTO and RPO goals cost-effectively. Creating an Amazon RDS cross-region read replica and configuring Amazon S3 Cross-Region Replication (CRR) ensures data is replicated asynchronously to the secondary region with minimal lag, satisfying the 15-minute RPO. Pre-configuring the Application Load Balancer and Auto Scaling group with desired capacity set to zero in the secondary region ensures compute costs are not incurred until a failover is initiated. Upon failover, the database replica is promoted and the Auto Scaling group is scaled up, which can be accomplished well within the 2-hour RTO.

Step-by-Step Solution

1
Analyze RTO, RPO, and cost constraints.
RTO is 2 hours (allows time to provision compute and promote databases), RPO is 15 minutes (requires continuous or highly frequent asynchronous replication), and costs must be minimized (favors Pilot Light or Warm Standby with resources scaled down).
Understanding the recovery boundaries is necessary to select the appropriate disaster recovery pattern.
2
Select the database and storage replication mechanism that satisfies the 15-minute RPO.
Amazon RDS cross-region read replicas use asynchronous replication with very low lag (usually seconds), meeting the 15-minute RPO. Amazon S3 Cross-Region Replication (CRR) replicates objects asynchronously, also meeting the 15-minute RPO.
This satisfies the data persistence requirements across regions within the allowed data loss envelope.
3
Select the compute staging mechanism that meets the 2-hour RTO while minimizing costs.
Deploying the Application Load Balancer and configuring the Auto Scaling group with the desired capacity set to zero minimizes compute costs, as no EC2 instances run during normal operations. Scaling up the group during failover takes minutes, fitting comfortably inside the 2-hour RTO.
This ensures the application layer is ready to be provisioned quickly without incurring active running costs.

Key Concept

Disaster Recovery (DR) strategies on AWS (specifically Pilot Light vs. Warm Standby / Hot Standby) and cross-region replication mechanisms for RDS and S3.
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Topics

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

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