SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs a stateless web application on Amazon EC2 instances behind an Application Load Balancer. The application experiences predictable traffic patterns: low traffic at night and high traffic during business hours. The company wants to optimize costs without compromising availability. Which two actions should be taken? (Choose two.)
⚠ Common exam trap
The trap here is assuming that Spot Instances are always the best cost-saving measure, but using them for all instances can jeopardize availability in a stateless web application, and detailed monitoring adds cost without addressing the predictable scaling need.
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 an Auto Scaling group with scheduled scaling to match the predictable traffic patterns.
Scheduled scaling aligns capacity with predictable traffic, scaling out during business hours and in at night to reduce costs. Purchasing Reserved Instances or Savings Plans for the baseline covers the continuously running capacity at a discount. Together, these actions optimize cost while maintaining availability. Other options either risk availability, add cost, or do not address the predictable pattern effectively.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Configure an Auto Scaling group with scheduled scaling to match the predictable traffic patterns.
Why this is correct
Scheduled scaling allows the Auto Scaling group to adjust capacity based on known traffic patterns, such as scaling out before business hours and scaling in at night. This ensures sufficient capacity during peaks and reduces costs during low-traffic periods by terminating unused instances. It directly addresses the predictable nature of the workload.
- ✗
Use a Network Load Balancer instead of an Application Load Balancer to reduce costs.
Why it's wrong here
A Network Load Balancer is designed for extreme performance and static IPs, and its pricing is based on capacity units. It is not necessarily cheaper than an Application Load Balancer for HTTP/HTTPS workloads, and it lacks layer 7 features like path-based routing. Switching would not address the cost optimization goal and could complicate the architecture.
- ✗
Enable detailed monitoring for the EC2 instances to improve scaling responsiveness.
Why it's wrong here
Detailed monitoring provides metrics at 1-minute intervals instead of 5-minute intervals, which can improve scaling responsiveness, but it incurs additional charges. For predictable traffic patterns, scheduled scaling is more cost-effective and precise than relying on detailed monitoring. Detailed monitoring does not directly reduce compute costs and may increase them.
- ✓
Purchase Reserved Instances or Savings Plans for the baseline capacity.
Why this is correct
Reserved Instances or Savings Plans provide significant discounts for the minimum baseline capacity that runs continuously. By covering the always-on portion with a commitment, the company reduces costs for the predictable baseline, while Auto Scaling handles the variable peak. This combination optimizes cost without sacrificing availability for the baseline.
- ✗
Use Spot Instances for all instances in the Auto Scaling group to reduce compute costs.
Why it's wrong here
Spot Instances can be interrupted with a two-minute warning, which could reduce availability if all instances are Spot and interruptions occur. While Spot can reduce costs, using them for all instances in a stateless web application behind an ALB may still cause capacity shortfalls during interruptions. A mixed approach or On-Demand/Reserved for baseline is safer for availability.
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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
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