SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs a microservices application on Amazon ECS with AWS Fargate. The application experiences variable traffic throughout the day, with peak hours during business hours and minimal traffic at night. The company wants to optimize costs without affecting performance. Which action should they take?
⚠ Common exam trap
The trap here is assuming that purchasing Reserved Instances is a universal cost-saving measure, but Fargate does not offer Reserved Instances; it uses Savings Plans instead.
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
✓
Configure ECS Service Auto Scaling to adjust the number of tasks based on demand.
ECS Service Auto Scaling dynamically adjusts task count based on demand, ensuring the application scales with traffic while minimizing costs during idle periods. This is the most direct and effective cost optimization for variable workloads on Fargate. Other options either do not apply to Fargate or do not provide automatic elasticity, risking higher costs or performance issues.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Purchase Reserved Instances for Fargate tasks.
Why it's wrong here
AWS Fargate does not support Reserved Instances. Fargate pricing is based on vCPU and memory resources consumed per second, with no long-term commitment options like Reserved Instances. Instead, you can use Compute Savings Plans, which apply to Fargate usage. Purchasing Reserved Instances is not possible for Fargate, so this action would not achieve cost optimization.
- ✓
Configure ECS Service Auto Scaling to adjust the number of tasks based on demand.
Why this is correct
ECS Service Auto Scaling automatically adjusts the desired count of tasks in a service based on metrics such as CPU utilization or request count. By scaling out during peak hours and scaling in during low-traffic periods, the company pays only for the resources needed, optimizing costs. This directly addresses the variable traffic pattern without manual intervention and maintains performance.
- ✗
Migrate the application to Amazon EC2 instances with Spot Instances.
Why it's wrong here
Migrating to EC2 Spot Instances could reduce compute costs, but it requires significant changes to the architecture, including managing instances and handling interruptions. Spot Instances are not ideal for a microservices application that may not be fault-tolerant. This is a complex migration that may not be cost-effective in the short term and could impact performance if not carefully designed.
- ✗
Use a larger Fargate task size to reduce the number of tasks.
Why it's wrong here
Using a larger task size might reduce the number of tasks, but it does not automatically adjust to traffic changes. If you provision for peak capacity, you overpay during low traffic; if you provision for low capacity, you may not handle peaks. This approach lacks elasticity and can lead to either higher costs or degraded performance, failing the optimization goal.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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.