Cross-Region read replica plus AMI copy and S3 CRR for disaster recovery

SAP-C02 By islever Editorial Last updated

Design a solution to ensure business continuity. Design a strategy to meet reliability requirements.

Short answer

C Replicate RDS to a cross-Region read replica for finance queries, copy AMIs, enable S3 CRR, and promote the replica during a disaster.

Question

A company needs to implement disaster recovery for a critical application that runs in a single AWS Region. The application's users interact with a web frontend that is hosted on Amazon EC2 instances behind an Application Load Balancer (ALB). The application writes to an Amazon RDS for MySQL DB instance. The application also outputs processed documents that are stored in an Amazon S3 bucket. The company’s finance team directly queries the database to run reports. During busy periods, these queries consume resources and negatively affect application performance. A solutions architect must design a solution that will provide resiliency during a disaster. The solution must minimize data loss and must resolve the performance problems that result from the finance team's queries. Which solution will meet these requirements?
  1. Migrate the database to Amazon DynamoDB and use DynamoDB global tables. Instruct the finance team to query a global table in a separate Region. Create an AWS Lambda function to periodically synchronize the contents of the original S3 bucket to a new S3 bucket in the separate Region. Launch EC2 instances and create an ALB in the separate Region. Configure the application to point to the new S3 bucket.
  2. Launch additional EC2 instances that host the application in a separate Region. Add the additional instances to the existing ALIn the separate Region, create a read replica of the RDS DB instance. Instruct the finance team to run queries against the read replica. Use S3 Cross-Region Replication (CRR) from the original S3 bucket to a new S3 bucket in the separate Region. During a disaster, promote the read replica to a standalone DB instance. Configure the application to point to the new S3 bucket and to the newly promoted read replica.
  3. Create a read replica of the RDS DB instance in a separate Region. Instruct the finance team to run queries against the read replica. Create AMIs of the EC2 instances that host the application frontend. Copy the AMIs to the separate Region. Use S3 Cross-Region Replication (CRR) from the original S3 bucket to a new S3 bucket in the separate Region. During a disaster, promote the read replica to a standalone DB instance. Launch EC2 instances from the AMIs and create an ALB to present the application to end users. Configure the application to point to the new S3 bucket. Correct Answer
  4. Create hourly snapshots of the RDS DB instance. Copy the snapshots to a separate Region. Add an Amazon ElastiCache cluster in front of the existing RDS database. Create AMIs of the EC2 instances that host the application frontend. Copy the AMIs to the separate Region. Use S3 Cross-Region Replication (CRR) from the original S3 bucket to a new S3 bucket in the separate Region. During a disaster, restore the database from the latest RDS snapshot. Launch EC2 instances from the AMIs and create an ALB to present the application to end users. Configure the application to point to the new S3 bucket.

Key Takeaways

A cross-Region read replica serves the finance reporting load continuously and can be promoted in seconds during a disaster, so recovery point is near zero and the reporting problem is solved by the same component.

A single-Region application behind an ALB writes to RDS for MySQL and outputs documents to S3, while finance queries on the primary database hurt application performance. The design must survive a regional disaster, minimize data loss, and fix the query contention.

Common mistake: Assuming an ALB can front instances in another Region. An Application Load Balancer is a regional service, so EC2 instances in a different Region cannot be added to an existing ALB, which is why option B cannot work.

Expert Analysis

Why the Answer Is Correct

Creating an RDS read replica in a second Region offloads the finance queries from the primary instance, resolving the performance problem, and it continuously replicates so a disaster loses almost no committed transactions. Copying AMIs of the frontend instances to that Region provides ready-to-launch capacity, S3 Cross-Region Replication keeps the processed documents mirrored, and during a disaster the replica is promoted to a standalone instance and EC2 plus ALB are launched from the copied AMIs.

Why the Other Options Are Wrong

A: Migrating a relational workload to DynamoDB is a re-architecture, not a disaster recovery mechanism, and a periodically invoked Lambda sync to S3 introduces data loss. B: An Application Load Balancer is a regional service, so EC2 instances in a separate Region cannot be added to the existing ALB. D: Hourly snapshots give an RPO of up to one hour, which fails the minimize-data-loss requirement, and ElastiCache does not resolve the reporting contention on a relational database.

Community Comment Notes

The community voted 92 to 1 for C. One commenter argued for B on the grounds that C omits redirecting the application to the promoted instance, but the standard answer holds because C explicitly covers replica promotion, AMI-based recovery, and S3 replication in a single Region-independent design.

Official Reference

https://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/USER_ReadReplicas.html

This link opens the official vendor documentation in a new tab.

Community Votes

C
100%

100% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 7 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 7

  1. pangchn 👍 7 Answered C
    C A is out since periodic lambda will have data loss B is out since ALB is regional service. Can't add EC2 to ALB if in different region D is out since hourly backup will have data loss
  2. txxxxxf 👍 2 Answered C
    This solution involves creating a Read Replica of the RDS DB instance in another region and directing the finance team to execute queries on it, minimizing application performance impact. AMIs of EC2 instances are created and copied for rapid deployment. S3 Cross-Region Replication ensures data safety. In a disaster, the Read Replica becomes a standalone DB, and EC2 instances from AMIs with a new ALB serve the application, all reconfigured to the new S3 bucket. This approach addresses disaster recovery, minimizes data loss, and mitigates query-induced performance issues with minimal application changes.
  3. AzureDP900 👍 1
    Option C involves creating a read replica of the RDS DB instance in a separate Region, which addresses the performance issue caused by the finance team's queries. This approach also ensures that the database is available during a disaster. Additionally, this option uses S3 Cross-Region Replication (CRR) to synchronize data across Regions, ensuring minimal data loss in case of a disaster. The use of a read replica and CRR provides a more efficient solution compared to options A or D, which involve synchronizing entire databases or restoring from snapshots.
  4. lasithasilva709 👍 1 Answered C
    A is out because relational database is suited here D is out because ElastiCache is not required and hourly snapshots of the RDS DB instance would not minimise data loss B is out because as per the requirements (no RTO is mentioned), there is no need to launch EC2 instances in DR site and keep them idle
  5. ahrentom 👍 1 Answered B
    I´ll go with B, because 1. C did not promote the Read Replica into a Standalone instance. 2. C did not redirect S3 traffic to the separate region, if the main region fails. Cost is not in focus, so we can preinstall the needed EC2 instances.
Show 2 more comments
  1. CMMC 👍 1 Answered C
    Read recplica for reporting, CRR to replicate S3 in another region, launch EC2 from AMI and ALB and promote the read replicate in the separate region furing DR
  2. Dgix 👍 1 Answered C
    C is the answer.

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