SAA-C03 Design Cost-Optimized Architectures Practice Question

A SaaS provider runs a multi-tenant application on Amazon RDS for PostgreSQL. The database is 2 TB and experiences steady read-heavy traffic during business hours. The provider wants to offload read traffic to reduce load on the primary instance and lower cost compared to scaling up the primary. The application can tolerate slightly stale reads for reporting queries. Which solution is MOST cost-effective?

⚠ Common exam trap

The trap here is assuming that a Multi-AZ standby instance can be used to serve read traffic, when it is inaccessible for normal operations.

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

✓

Create a read replica and route reporting queries to it.

A read replica offloads read-only reporting queries from the primary instance, reducing contention and allowing the primary to remain appropriately sized. Because asynchronous replication introduces slight lag, the application's tolerance for stale reads makes this acceptable. This approach is more cost-effective than scaling up the primary or enabling Multi-AZ, which does not provide readable standby 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.

✗
Enable Multi-AZ deployment and route reporting queries to the standby instance.
Why it's wrong here
A Multi-AZ standby instance is not accessible for read or write operations; it exists solely for automatic failover. Routing queries to it is not possible. Enabling Multi-AZ doubles the cost of the primary instance without providing any read scaling benefit. While Multi-AZ improves availability, it does not address the requirement to offload read traffic or reduce cost for read-heavy reporting.
✗
Migrate the database to Amazon DynamoDB with on-demand capacity mode.
Why it's wrong here
DynamoDB is a NoSQL key-value and document database, while the application uses PostgreSQL, a relational database. Migrating would require significant schema and application changes, and DynamoDB does not support complex SQL joins or transactions in the same way. On-demand capacity mode can be cost-effective for unpredictable workloads, but the migration effort and loss of relational features make this option impractical and likely more expensive overall.
✓
Create a read replica and route reporting queries to it.
Why this is correct
A read replica is a separate RDS instance that receives asynchronous replication from the primary. It offloads read-only reporting queries, reducing load on the primary and allowing the primary to remain at its current size. Because the application tolerates slightly stale reads, asynchronous replication lag is acceptable. The read replica can be sized independently and stopped or scaled down when not needed, making it more cost-effective than scaling up the primary.
✗
Increase the size of the primary RDS instance to a larger instance class.
Why it's wrong here
Scaling up the primary instance increases its CPU and memory, which may handle more read traffic, but it also increases cost linearly and does not isolate reporting queries from transactional workloads. The primary instance still serves all reads and writes, so reporting queries can still impact latency for the application. This approach is less cost-effective than offloading reads to a separate replica that can be sized and managed independently.

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SAA-C03 Design Cost-Optimized Architectures Practice Question

Why each option matters

Option-by-option breakdown

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