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SAA-C03 · Question #592

A company uses an Amazon RDS for MySQL instance. To prepare for end-of-year processing, the company added a read replica to accommodate extra read-only queries from the company's reporting tool. The…

The correct answer is B. Resize the read replica to a smaller instance size Do not make changes to the primary instance. The read replica is over-provisioned after the peak period, while the primary instance maintains a moderate workload. Rightsizing involves scaling down the underutilized read replica to reduce costs while keeping the primary instance stable to handle its current load and allow…

Submitted by neha2k· Mar 4, 2026Design Cost-Optimized Architectures

Question

A company uses an Amazon RDS for MySQL instance. To prepare for end-of-year processing, the company added a read replica to accommodate extra read-only queries from the company's reporting tool. The read replica CPU usage was 60% and the primary instance CPU usage was 60%. After end-of-year activities are complete, the read replica has a constant 25% CPU usage. The primary instance still has a constant 60% CPU usage. The company wants to rightsize the database and still provide enough performance for future growth. Which solution will meet these requirements?

Options

  • ADelete the read replica Do not make changes to the primary instance
  • BResize the read replica to a smaller instance size Do not make changes to the primary instance
  • CResize the read replica to a larger instance size Resize the primary instance to a smaller instance
  • DDelete the read replica Resize the primary instance to a larger instance

How the community answered

(37 responses)
  • A
    3% (1)
  • B
    81% (30)
  • C
    5% (2)
  • D
    11% (4)

Why each option

The read replica is over-provisioned after the peak period, while the primary instance maintains a moderate workload. Rightsizing involves scaling down the underutilized read replica to reduce costs while keeping the primary instance stable to handle its current load and allow for future growth.

ADelete the read replica Do not make changes to the primary instance

Deleting the read replica entirely would remove the read scaling capabilities and offload the remaining 25% CPU usage back to the primary instance, potentially increasing the primary's load or removing a valuable scaling component.

BResize the read replica to a smaller instance size Do not make changes to the primary instanceCorrect

The read replica's CPU usage dropped to a constant 25% after the end-of-year activities, indicating it is over-provisioned for its current workload. Resizing it to a smaller instance size will reduce costs without impacting performance, as 25% usage on a smaller instance could still be efficient. The primary instance's 60% CPU usage suggests it is appropriately sized, making no changes to it suitable for ensuring continued performance and allowing for future growth if its workload increases.

CResize the read replica to a larger instance size Resize the primary instance to a smaller instance

Resizing the read replica to a larger instance size is incorrect because its CPU usage is already low (25%), indicating it is over-provisioned. Resizing the primary instance to a smaller size is risky when it's already at 60% CPU utilization, as it might lead to performance degradation.

DDelete the read replica Resize the primary instance to a larger instance

Deleting the read replica is inappropriate if it still has a constant 25% CPU usage, as it indicates an ongoing read workload. Resizing the primary instance to a larger instance is not necessary when it's at 60% CPU, as the goal is rightsizing and it's not currently overutilized to justify a larger instance.

Concept tested: RDS instance rightsizing and read replica management

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

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