- A
Use Aurora Serverless v2 for the relational order system.
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.
- B
Use DynamoDB on-demand capacity for the shopping-cart profile store.
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.
- C
Keep both workloads on large provisioned RDS instances and add read replicas for the cart store.
Why wrong: Incorrect. This keeps both systems on fixed-capacity relational infrastructure even where a simpler managed database would be cheaper. The cart workload does not justify expensive relational replicas.
- D
Use DynamoDB provisioned capacity with a fixed minimum despite the unpredictable traffic.
Why wrong: 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.
- E
Replace the relational order system with a wide-column table to reduce SQL licensing.
Why wrong: 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.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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.
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 and memory capacity based on application demand, making it ideal for unpredictable traffic. It eliminates the need to provision for peak load, reducing costs by scaling to zero when idle. This matches the requirement to avoid paying for large idle database instances.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Keep both workloads on large provisioned RDS instances and add read replicas for the cart store.
Why it's wrong here
Incorrect. This keeps both systems on fixed-capacity relational infrastructure even where a simpler managed database would be cheaper. The cart workload does not justify expensive relational replicas.
When this WOULD be correct
This option would be correct in a scenario where the workload is predictable with steady traffic, and the primary concern is high availability and read scalability for the shopping cart store, not cost optimization for idle resources.
- ✗
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.
When this WOULD be correct
This option would be correct if the question specified that the workload has predictable traffic patterns with known peaks and troughs, and the company wants to optimize cost by reserving capacity at a baseline level while allowing bursts within provisioned limits.
- ✗
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.
When this WOULD be correct
If the question asked for a cost-effective, scalable solution for a non-relational workload (e.g., storing user session data) with unpredictable traffic and no need for complex queries, a wide-column store like DynamoDB on-demand would be correct.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The SAA-C03 exam frequently reuses these exact scenarios with slightly different constraints.
✓Use Aurora Serverless v2 for the relational order system.Correct answer▾
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.
✗Keep both workloads on large provisioned RDS instances and add read replicas for the cart store.Wrong answer — click to see why▾
Why this is wrong here
Option C is wrong because it suggests keeping both workloads on large provisioned RDS instances, which contradicts the requirement to avoid paying for large idle database instances due to unpredictable traffic. Read replicas do not address the cost of idle capacity.
★ When this WOULD be the correct answer
This option would be correct in a scenario where the workload is predictable with steady traffic, and the primary concern is high availability and read scalability for the shopping cart store, not cost optimization for idle resources.
Why candidates choose this
Candidates may be tempted by the familiarity of RDS and read replicas for scaling reads, overlooking the cost implications of provisioned capacity for unpredictable traffic.
✗Use DynamoDB provisioned capacity with a fixed minimum despite the unpredictable traffic.Wrong answer — click to see why▾
Why this is wrong here
DynamoDB provisioned capacity with a fixed minimum does not suit unpredictable traffic because it requires manual scaling and may lead to throttling during spikes or wasted capacity during lulls, contradicting the goal of avoiding paying for large idle instances.
★ When this WOULD be the correct answer
This option would be correct if the question specified that the workload has predictable traffic patterns with known peaks and troughs, and the company wants to optimize cost by reserving capacity at a baseline level while allowing bursts within provisioned limits.
Why candidates choose this
Candidates may think provisioned capacity offers cost control and assume a fixed minimum is sufficient, overlooking that unpredictable traffic requires on-demand or auto-scaling to avoid both throttling and waste.
✗Replace the relational order system with a wide-column table to reduce SQL licensing.Wrong answer — click to see why▾
Why this is wrong here
Replacing the relational order system with a wide-column table would lose ACID transactions and relational integrity needed for order processing, and SQL licensing is not a concern with Aurora or RDS.
★ When this WOULD be the correct answer
If the question asked for a cost-effective, scalable solution for a non-relational workload (e.g., storing user session data) with unpredictable traffic and no need for complex queries, a wide-column store like DynamoDB on-demand would be correct.
Why candidates choose this
Candidates may think wide-column stores are always cheaper and simpler, overlooking the specific relational requirements of order systems and the fact that SQL licensing is irrelevant for AWS managed databases.
Analysis generated from the official SAA-C03blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may choose provisioned capacity (Option D) thinking it is cheaper, but for unpredictable traffic, on-demand avoids over-provisioning costs, and Aurora Serverless v2 is the relational equivalent of this elastic model.
Detailed technical explanation
How to think about this question
Aurora Serverless v2 uses a shared storage volume and scales in ACU (Aurora Capacity Units) increments as low as 0.5 ACU, with sub-second scaling to handle sudden spikes. DynamoDB on-demand capacity charges per request (read/write units) with no minimum, automatically adjusting to traffic patterns, which is cost-effective for unpredictable workloads. Under the hood, DynamoDB on-demand uses a burst pool and adaptive capacity to handle spikes without throttling.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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 |
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use Aurora Serverless v2 for the relational order system. — Aurora Serverless v2 automatically scales compute and memory capacity based on application demand, making it ideal for unpredictable traffic. It eliminates the need to provision for peak load, reducing costs by scaling to zero when idle. This matches the requirement to avoid paying for large idle database instances.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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