SAA-C03 Design Cost-Optimized Architectures Practice Question
A SaaS vendor has a steady 24/7 control plane on ECS and several small event-driven tasks that currently run on a separate always-on service. Management wants the billing discount that applies across both ECS and Lambda usage without committing to a specific instance family. Which two actions are best? Select two.
⚠ Common exam trap
A common mix-up: candidates confuse Savings Plans with Reserved Instances or Spot Instances, assuming a specific instance family commitment is required, or they think Spot Instances can replace a billing discount mechanism for a steady workload.
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
✓
Buy a Compute Savings Plan for the predictable baseline usage.
A Compute Savings Plan offers the largest discount (up to 66%) across both ECS and Lambda usage without committing to a specific instance family, which matches the requirement to cover both services flexibly. It applies to any EC2 instance, including those used by ECS, and to AWS Lambda compute, making it ideal for a mixed workload with a predictable baseline.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Buy a Compute Savings Plan for the predictable baseline usage.
Why this is correct
Correct. A Compute Savings Plan discounts predictable compute spend across ECS and Lambda without binding the team to one instance family. That flexibility matches a mixed compute estate and avoids overcommitting.
- ✓
Move the event-driven tasks to AWS Lambda instead of keeping a separate always-on service.
Why this is correct
Correct. Lambda removes idle server cost for small, infrequent tasks and fits event-driven processing well. This lowers operational overhead and avoids paying for a service that mostly waits for work.
- ✗
Buy an EC2 Instance Savings Plan tied to one instance family for all workloads.
Why it's wrong here
Incorrect. An EC2 Instance Savings Plan is more restrictive than a Compute Savings Plan and does not cover the Lambda portion of the estate. The vendor would lose flexibility without improving coverage.
When this WOULD be correct
This option would be correct if the question asked for the best discount for a workload running entirely on EC2 instances of a known, consistent family, with no serverless components like Lambda.
- ✗
Use Spot Instances for the control plane because it is the largest bill.
Why it's wrong here
Incorrect. Control planes usually require steady availability and should not depend on interruptible capacity. Spot is a poor fit when service stability matters more than the last increment of savings.
When this WOULD be correct
A question where a non-critical, fault-tolerant workload (e.g., batch processing, data analysis) runs on EC2 and the goal is to reduce costs by up to 90% without needing a discount plan covering Lambda. The workload must handle interruptions gracefully.
- ✗
Increase the ECS desired count so Lambda can be removed.
Why it's wrong here
Incorrect. More ECS tasks mean more always-on compute cost, which directly conflicts with the cost-reduction goal. It also adds unnecessary operational burden instead of reducing it.
When this WOULD be correct
If the question asked for a way to handle variable workloads by scaling ECS tasks instead of using Lambda, and the goal was to consolidate all compute on ECS for simplicity, then increasing ECS desired count could 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.
✓Buy a Compute Savings Plan for the predictable baseline usage.Correct answer▾
Why this is correct
Correct. A Compute Savings Plan discounts predictable compute spend across ECS and Lambda without binding the team to one instance family. That flexibility matches a mixed compute estate and avoids overcommitting.
✗Buy an EC2 Instance Savings Plan tied to one instance family for all workloads.Wrong answer — click to see why▾
Why this is wrong here
An EC2 Instance Savings Plan is tied to a specific instance family and region, which does not cover Lambda usage. The question requires a discount that applies across both ECS and Lambda, so a Compute Savings Plan is needed instead.
★ When this WOULD be the correct answer
This option would be correct if the question asked for the best discount for a workload running entirely on EC2 instances of a known, consistent family, with no serverless components like Lambda.
Why candidates choose this
Candidates may confuse Instance Savings Plans with Compute Savings Plans, or assume that all Savings Plans cover all compute services, not realizing the family/region restriction on Instance Savings Plans.
✗Use Spot Instances for the control plane because it is the largest bill.Wrong answer — click to see why▾
Why this is wrong here
The control plane runs 24/7 and is steady, so it is not suitable for Spot Instances, which can be interrupted. The question asks for a discount covering both ECS and Lambda, but Spot Instances only apply to EC2, not Lambda.
★ When this WOULD be the correct answer
A question where a non-critical, fault-tolerant workload (e.g., batch processing, data analysis) runs on EC2 and the goal is to reduce costs by up to 90% without needing a discount plan covering Lambda. The workload must handle interruptions gracefully.
Why candidates choose this
Candidates know Spot Instances offer large discounts and may assume they apply to any EC2-based workload, overlooking the interruption risk and the requirement for a discount covering both ECS and Lambda.
✗Increase the ECS desired count so Lambda can be removed.Wrong answer — click to see why▾
Why this is wrong here
Increasing ECS desired count does not provide a billing discount across ECS and Lambda usage; it only increases ECS costs and does not eliminate the need for Lambda or provide a savings plan.
★ When this WOULD be the correct answer
If the question asked for a way to handle variable workloads by scaling ECS tasks instead of using Lambda, and the goal was to consolidate all compute on ECS for simplicity, then increasing ECS desired count could be correct.
Why candidates choose this
Candidates may think that running more on ECS reduces the need for separate services, but they overlook that this does not achieve the desired discount across both services and may increase costs.
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
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.