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.
A is correct because Aurora Serverless v2 automatically scales database capacity in fine-grained ACUs up and down based on actual load, so the relational order system only consumes (and bills for) the capacity it needs during unpredictable traffic, avoiding large idle provisioned instances. B is correct because DynamoDB on-demand capacity mode charges per request and instantly accommodates unpredictable traffic spikes without provisioning or managing capacity, which fits the key-value shopping-cart profile store. C is wrong because large provisioned RDS instances plus read replicas still pay for idle capacity and read replicas do not address write-side traffic variability. D is wrong because DynamoDB provisioned capacity with a fixed minimum requires capacity planning and either throttles or wastes money under unpredictable traffic. E is wrong because replacing the relational order system with a wide-column store does not reduce SQL licensing (Aurora is not licensed per-core like commercial engines) and abandons the relational model the orders workload requires.
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
Aurora Serverless v2 scales capacity automatically in fine-grained increments based on actual load, so the relational order system pays only for consumed capacity during unpredictable traffic. This directly satisfies the requirement to avoid paying for large idle database instances without application rewrites.
- ✓
Use DynamoDB on-demand capacity for the shopping-cart profile store.
Why this is correct
DynamoDB on-demand capacity charges per request rather than for provisioned throughput, so the key-value cart store incurs no cost when idle. This satisfies the unpredictable-traffic constraint and suits the simple key-value access pattern without capacity planning.
- ✗
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.