SAA-C03 Design High-Performing Architectures Practice Question

A financial analytics company runs an Amazon RDS for MySQL database that supports a read-heavy web application. The primary DB instance is heavily loaded during business hours, and read replicas are already deployed and receiving traffic from the application. The team wants to reduce the load on the primary DB instance caused by read queries as much as possible, while keeping the application changes minimal. Which action should a solutions architect take?

⚠ Common exam trap

The trap here is assuming Multi-AZ standbys can serve read traffic to offload the primary, when they are actually passive failover targets.

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

✓

Configure the application to send read queries to the existing read replicas instead of the primary DB instance.

Read replicas exist precisely to offload read-only query traffic from a primary DB instance. Since replicas are already deployed and receiving some traffic, routing the application's read queries to them reduces contention on the primary with minimal change. Multi-AZ is for availability, vertical scaling adds cost without offloading reads, and introducing a cache is a larger architectural change that does not use existing replica capacity.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Increase the size of the primary DB instance to a larger instance class.
Why it's wrong here
Scaling the primary instance up gives it more CPU, memory, and IOPS, which can absorb more read load, but it does not remove read queries from the primary. The primary still processes every read sent to it, so this is a costly vertical scaling approach rather than an architectural offload. Read replicas already exist and are the intended mechanism for separating read traffic from the primary.
✗
Enable Multi-AZ deployment on the primary DB instance.
Why it's wrong here
Multi-AZ maintains a synchronous standby in a different Availability Zone for high availability and failover, but the standby does not serve read traffic under normal operation. It therefore does nothing to offload read queries from the primary. This scenario already has read replicas handling reads, so adding Multi-AZ would not reduce primary read pressure and would only add cost and a failover target.
✓
Configure the application to send read queries to the existing read replicas instead of the primary DB instance.
Why this is correct
Read replicas are designed to serve read-only traffic using MySQL's asynchronous replication. Directing the application's read queries to the existing replicas removes that read load from the primary DB instance, which is the goal here. Because replicas are already deployed and receiving some traffic, extending application read routing to them is the minimal-change, correct optimization for reducing primary load.
✗
Create an Amazon ElastiCache for Redis cluster and cache all read results.
Why it's wrong here
Caching can reduce database reads, but it requires application changes to read from and invalidate the cache, and it does not directly use the existing read replicas. The scenario asks for minimal application change and the replicas are already in place. Introducing a new caching layer adds complexity, cache invalidation concerns, and cost without leveraging the deployed read capacity.

Go deeper

SAA-C03 Design High-Performing Architectures Practice Question

Why each option matters

Option-by-option breakdown

Related to this question