Cost-Optimized RDS Read Replica for Reporting Workloads

SAA-C03 By islever Editorial Last updated

Design cost-optimized database solutions.

Short answer

D Create a read replica in us-east-1 to handle reporting queries, reducing load on the primary instance while avoiding cross-region data transfer costs.

Question

A company uses Amazon RDS for PostgreSQL to run its applications in the us-east-1 Region. The company also uses machine learning (ML) models to forecast annual revenue based on near real-time reports. The reports are generated by using the same RDS for PostgreSQL database. The database performance slows during business hours. The company needs to improve database performance. Which solution will meet these requirements MOST cost-effectively?
  1. Create a cross-Region read replica. Configure the reports to be generated from the read replica.
  2. Activate Multi-AZ DB instance deployment for RDS for PostgreSQL. Configure the reports to be generated from the standby database.
  3. Use AWS Data Migration Service (AWS DMS) to logically replicate data to a new database. Configure the reports to be generated from the new database.
  4. Create a read replica in us-east-1. Configure the reports to be generated from the read replica. Correct Answer

Key Takeaways

The core concept tested is separating write and read workloads using read replicas; the common trap is choosing Multi-AZ for read scaling, which does not support reading from the standby instance.

This question addresses how to offload heavy reporting queries from a primary Amazon RDS for PostgreSQL instance using a read replica. It establishes that an in-region read replica is the most cost-effective method to improve database performance without incurring cross-region data transfer fees or Multi-AZ standby costs.

Common mistake: Candidates often select Multi-AZ (Option B) because it provides high availability, but they fail to realize that Multi-AZ standbys are strictly for disaster recovery and cannot be used to handle read traffic, making them ineffective for this specific performance requirement.

Expert Analysis

Why the Answer Is Correct

Creating a read replica within the same Region (us-east-1) allows the application to direct read-heavy reporting queries away from the primary database instance. This reduces I/O contention on the primary, thereby improving performance for both transactional and reporting workloads. Since the replica is in the same region, there are no cross-region data transfer costs, making it significantly more cost-effective than a cross-Region replica.

Why the Other Options Are Wrong

Option A is incorrect because cross-Region replicas incur significant data transfer costs across AWS regions, violating the 'MOST cost-effectively' constraint. Option B is incorrect because Amazon RDS Multi-AZ deployments use synchronous replication for high availability, but the standby instance is not accessible for read operations; it only fails over if the primary becomes unavailable. Option C is incorrect because AWS DMS is primarily designed for continuous replication and migration rather than serving as a low-latency read target for real-time reporting, and it adds unnecessary operational complexity compared to native read replicas.

Community Comment Notes

The community consensus strongly supports Option D, with users highlighting that read replicas avoid the overhead of cross-region transfers and Multi-AZ standby maintenance costs. As one commenter noted, "Read replicas are typically less expensive than setting up a cross-Region replica or activating Multi-AZ deployments," emphasizing the cost savings inherent in same-region replication.

Official Reference

These links open the official vendor documentation in a new tab.

Exam Strategy

Always check the 'cost-effectiveness' constraint when comparing storage or compute solutions. Remember that Multi-AZ is for availability, not scalability, while Read Replicas are for both availability (optional) and read scalability.

Frequently Asked Questions

Why can't I use the Multi-AZ standby for reports?

Multi-AZ standbys are strictly for failover and are not exposed for endpoint connections. You cannot route read traffic to them.

Is a cross-Region replica ever cheaper?

No, cross-Region replicas incur data transfer charges between regions, making them more expensive than same-region replicas for identical functionality.

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Community Votes

D
100%

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

Discussion 3 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 3

  1. muhammadahmer36 👍 1 Answered D
    Read replicas are typically less expensive than setting up a cross-Region replica or activating Multi-AZ deployments. You only pay for the additional read replica, without the overhead costs associated with cross-Region data transfer or maintaining a synchronous standby in Multi-AZ setups.
  2. [Removed] 👍 1 Answered D
    D. Create a read replica in us-east-1. Configure the reports to be generated from the read replica.
  3. hpirnaj 👍 1 Answered D
    MOST cost-effectively

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