SAA-C03 Design Cost-Optimized Architectures Practice Question
A product catalog system uses a relational database for orders and a simple key-value profile store for shopping carts. Traffic is unpredictable, and the company wants to avoid paying for large idle database instances. Which two choices are best? Select two.
⚠ Common exam trap
Test-takers frequently think provisioned capacity with a minimum is acceptable for unpredictable traffic, but the question explicitly requires avoiding paying for idle capacity, so on-demand or serverless options are the only correct choices.
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
✓
Use Aurora Serverless v2 for the relational order system.
Aurora Serverless v2 automatically scales compute capacity up and down based on demand, so you only pay for the resources you use. This eliminates the need to provision for peak traffic and avoids paying for large idle database instances, making it cost-optimized for unpredictable workloads.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Use Aurora Serverless v2 for the relational order system.
Why this is correct
Correct. Aurora Serverless v2 is designed for variable relational workloads because capacity can scale without constantly paying for a large fixed instance. It preserves SQL features while reducing idle overprovisioning.
- ✓
Use DynamoDB on-demand capacity for the shopping-cart profile store.
Why this is correct
Correct. On-demand capacity fits unpredictable key-value traffic and avoids the need to guess throughput in advance. It is a strong cost choice when access patterns are variable and the schema is simple.
- ✗
Keep both workloads on large provisioned RDS instances and add read replicas for the cart store.
Why it's wrong here
Provisioned RDS instances incur charges regardless of utilisation, directly contradicting the requirement to avoid paying for large idle database instances when traffic is unpredictable. The cart store’s key-value workload does not benefit from relational read replicas, which replicate transactional SQL data rather than providing the elastic, serverless scaling needed for unpredictable traffic. This option would be correct if the cart store required ACID-compliant relational queries and the company accepted fixed-cost provisioning for predictable peak loads.
- ✗
Use DynamoDB provisioned capacity with a fixed minimum despite the unpredictable traffic.
Why it's wrong here
Incorrect. Fixed provisioned capacity can be cheaper only when traffic is stable and predictable. Here, the company explicitly wants to avoid paying for idle capacity during variable demand.
- ✗
Replace the relational order system with a wide-column table to reduce SQL licensing.
Why it's wrong here
Incorrect. Replacing the relational system would force a redesign and remove the SQL and transaction model that order processing usually needs. Cost optimization should not break the application requirements.
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 by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.