SAA-C03 Design Cost-Optimized Architectures Practice Question
A company has a steady, predictable workload that must run continuously (24/7) in a single AWS Region. The team wants the lowest cost option available for this steady usage, but also expects they may choose different EC2 instance families in the future (without re-buying compute discounts). Which AWS purchase option best meets these goals?
⚠ Common exam trap
Test-takers frequently confuse Reserved Instances (which lock instance family and AZ) with Savings Plans (which offer regional flexibility), leading them to choose Standard Reserved Instances despite the stated requirement for future instance family changes.
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
✓
Compute Savings Plans, committed for a 1- to 3-year term in the Region
Compute Savings Plans offer the lowest cost for steady, predictable workloads while providing instance family flexibility within a Region. Unlike Reserved Instances, they automatically apply discounts to any EC2 instance family (and even Fargate/Lambda) in the chosen Region, so the company can switch instance families in the future without losing the discount. A 1- or 3-year commitment yields significant savings (up to 66%) compared to On-Demand, making it the optimal choice for this scenario.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
On-Demand Instances only, because they automatically adjust to future needs
Why it's wrong here
On-Demand Instances provide flexibility, but they do not offer discounted pricing through a commitment. For a predictable 24/7 workload, a commitment-based option (Savings Plans or Reserved Instances) is typically required to achieve the lowest cost.
When this WOULD be correct
On-Demand Instances would be correct for a question where the workload is unpredictable, short-term, or variable, and the priority is maximum flexibility with no upfront commitment, such as for a new application with unknown usage patterns.
- ✓
Compute Savings Plans, committed for a 1- to 3-year term in the Region
Why this is correct
Compute Savings Plans provide discounted pricing in exchange for committing to a consistent hourly spend (scoped to a Region). They apply to EC2 usage and are flexible enough that you can change EC2 instance families over time while still receiving the Savings Plans discount within the commitment scope.
- ✗
Standard Reserved Instances tied to a single instance type and Availability Zone
Why it's wrong here
Standard Reserved Instances can be discounted, but they are much less flexible for changing instance families. If you switch to different instance types/families over time, you may not be covered by the original RI (or you would need exchanges that may reduce the economic benefit).
When this WOULD be correct
A company has a predictable, steady workload that requires a specific instance type and is willing to commit to an Availability Zone for maximum discount, and does not need flexibility to change instance families.
- ✗
EC2 Spot Instances, because they are always cheaper than savings programs
Why it's wrong here
Spot Instances can be cheaper, but their price is variable and capacity can be reclaimed, causing interruptions. For a workload required to run continuously (24/7), Spot is generally not the best fit unless the architecture can tolerate termination and the business requirements allow interruption.
When this WOULD be correct
For a fault-tolerant, stateless application that can handle interruptions (e.g., batch processing, big data, or containerized workloads) and where the lowest possible compute cost is desired, Spot Instances would be the correct choice.
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.
✓Compute Savings Plans, committed for a 1- to 3-year term in the RegionCorrect answer▾
Why this is correct
Compute Savings Plans provide discounted pricing in exchange for committing to a consistent hourly spend (scoped to a Region). They apply to EC2 usage and are flexible enough that you can change EC2 instance families over time while still receiving the Savings Plans discount within the commitment scope.
✗On-Demand Instances only, because they automatically adjust to future needsWrong answer — click to see why▾
Why this is wrong here
On-Demand Instances are the most expensive option for steady, 24/7 workloads, as they lack the discounts of committed-use plans. The question specifically asks for the lowest cost, so On-Demand does not meet that requirement.
★ When this WOULD be the correct answer
On-Demand Instances would be correct for a question where the workload is unpredictable, short-term, or variable, and the priority is maximum flexibility with no upfront commitment, such as for a new application with unknown usage patterns.
Why candidates choose this
Candidates may think On-Demand is the simplest and most flexible choice, and they might overlook the cost savings of committed-use plans for steady workloads, focusing only on the flexibility aspect mentioned in the option.
✗Standard Reserved Instances tied to a single instance type and Availability ZoneWrong answer — click to see why▾
Why this is wrong here
Standard Reserved Instances lock you into a specific instance type and Availability Zone, which contradicts the requirement to choose different instance families in the future without re-buying compute discounts.
★ When this WOULD be the correct answer
A company has a predictable, steady workload that requires a specific instance type and is willing to commit to an Availability Zone for maximum discount, and does not need flexibility to change instance families.
Why candidates choose this
Candidates may assume Reserved Instances always offer the best savings for steady workloads, overlooking the flexibility limitations that make Compute Savings Plans more suitable here.
✗EC2 Spot Instances, because they are always cheaper than savings programsWrong answer — click to see why▾
Why this is wrong here
Spot Instances can be interrupted with a 2-minute notice, making them unsuitable for a steady, continuous 24/7 workload that must run without interruption.
★ When this WOULD be the correct answer
For a fault-tolerant, stateless application that can handle interruptions (e.g., batch processing, big data, or containerized workloads) and where the lowest possible compute cost is desired, Spot Instances would be the correct choice.
Why candidates choose this
Candidates may assume Spot Instances are always the cheapest option and overlook the interruption risk, focusing only on cost without considering the workload's need for continuous availability.
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?”
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
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