SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs an internal analytics application in a single AWS Region. A solutions architect is reviewing the Amazon RDS for MySQL deployment and finds a Multi-AZ DB instance with a standby in another Availability Zone, used only for failover. The application performs many read-heavy queries against the primary instance, driving up instance size and cost. The team wants to offload read traffic and reduce the primary instance size. Which change should the architect recommend?
⚠ Common exam trap
The trap here is assuming the Multi-AZ standby can serve read traffic, when a Multi-AZ DB instance standby is strictly for failover and never handles application reads.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Add RDS read replicas and direct read-heavy queries to them.
Adding RDS read replicas moves read-heavy queries onto separate instances, relieving the primary and enabling a smaller, cheaper primary instance. The Multi-AZ standby exists only for failover and cannot serve reads, so the architect should introduce read replicas rather than re-architecting the deployment or switching database engines.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Convert the deployment to a Multi-AZ DB cluster with two readable standbys.
Why it's wrong here
A Multi-AZ DB cluster does provide readable standbys, but it is a different deployment topology that changes the failover model and can cost more than adding targeted read replicas. The team's immediate goal is to offload reads and reduce the primary size economically, and adding read replicas achieves that with less disruption than re-architecting the deployment.
- ✗
Migrate the database to Amazon DynamoDB with on-demand capacity.
Why it's wrong here
DynamoDB is a NoSQL key-value store, and migrating a relational MySQL analytics application would require significant schema and query rewrites that are out of scope and risky. The scenario asks how to offload reads and reduce cost on the existing relational deployment, not to change database engines, so this is a disproportionate and misaligned response.
- ✓
Add RDS read replicas and direct read-heavy queries to them.
Why this is correct
RDS read replicas serve read-only traffic on separate instances, letting the team offload read-heavy queries and shrink the primary instance. This directly addresses the cost driver, which is an oversized primary handling both reads and writes, and it works within a single Region while the Multi-AZ standby continues to provide high availability for failover.
- ✗
Enable RDS Performance Insights and rely on it to reduce query cost.
Why it's wrong here
Performance Insights is a monitoring and diagnostics tool that helps identify problematic queries, but it does not execute queries elsewhere or reduce the load on the primary instance. It can inform optimization decisions, yet by itself it will not offload read traffic or allow the primary instance to be downsized, so it fails to solve the stated problem.
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Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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