SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs an internal analytics application on Amazon RDS for PostgreSQL. The database is used heavily from 08:00 to 18:00 on weekdays, but outside those hours it receives almost no queries. The company must keep the database available at all times and cannot tolerate downtime during business hours. The team wants to reduce the cost of running this database. Which approach is the MOST cost-effective while meeting the availability requirement?
⚠ Common exam trap
The trap here is treating any idle period as an opportunity to stop the database, when the requirement for continuous availability rules out stopping and favors a capacity model that scales down while staying online.
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
✓
Migrate the workload to Aurora Serverless v2 with a minimum capacity that scales down during idle periods.
The workload has a sharp, predictable busy period and long idle windows, yet the database must remain available at all times. Aurora Serverless v2 capacity scales down during idle periods without stopping the database, so the company pays far less during the quiet hours while preserving continuous availability, which is the most cost-effective option that satisfies the constraint.
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 DB instance to a Multi-AZ deployment and purchase a Reserved Instance for the primary instance.
Why it's wrong here
Multi-AZ improves availability by maintaining a synchronous standby in another Availability Zone, but the standby doubles the instance cost and cannot serve read traffic in RDS for PostgreSQL. Purchasing a Reserved Instance helps the rate, yet the duplicated standby capacity makes this combination more expensive than the current single-instance deployment, so it does not reduce cost.
- ✗
Enable Aurora Auto Scaling with a reader endpoint and route all read queries to the reader.
Why it's wrong here
Aurora Auto Scaling adds and removes Aurora Replicas based on load, which helps read-heavy workloads, but the scenario is an RDS for PostgreSQL deployment and the workload is quiet rather than read-bound outside business hours. Replicas still incur instance-hour charges while running, and this does not address the primary instance's idle-period cost, so it does not lower total cost here.
- ✗
Stop the DB instance every evening and start it again each weekday morning.
Why it's wrong here
Stopping an RDS instance stops the instance-hour billing, but it violates the requirement to keep the database available at all times, and a stopped instance cannot accept connections. RDS also automatically restarts stopped instances after seven days, and stop/start operations take time, so this approach would introduce unavailability and is not acceptable.
- ✓
Migrate the workload to Aurora Serverless v2 with a minimum capacity that scales down during idle periods.
Why this is correct
Aurora Serverless v2 scales capacity in fine-grained increments and can scale down to a low minimum during idle periods while remaining available to accept connections. Because the database is almost unused outside business hours but must stay online, this pay-for-what-you-use capacity model reduces cost more effectively than a fixed-size RDS instance that bills the same rate around the clock.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
This SAA-C03 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SAA-C03 exam.