SAA-C03 Design Cost-Optimized Architectures Practice Question
A company runs a web application on AWS and wants to reduce costs. The application uses an Application Load Balancer (ALB) to distribute traffic to Amazon EC2 instances in an Auto Scaling group. The company observes that the EC2 instances are underutilized during off-peak hours. They want to optimize costs without affecting performance during peak hours. Which two actions should they take? (Choose two.)
⚠ Common exam trap
The trap here is assuming that using Spot Instances for all capacity is a straightforward cost-saving measure, but it can jeopardize availability for a web application that must maintain performance; a mixed policy is safer and still cost-effective.
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 the Auto Scaling group to use a mixed instances policy with a percentage of On-Demand and Spot Instances.
Scheduled scaling reduces capacity during predictable off-peak periods, directly cutting EC2 costs. A mixed instances policy with On-Demand and Spot balances cost savings with reliability, ensuring performance during peaks. Together, these actions optimize costs without impacting performance. Other options either do not directly save costs, introduce risk, or are not feasible.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable Application Load Balancer access logs and analyze them to identify cost-saving opportunities.
Why it's wrong here
Enabling ALB access logs provides visibility into traffic patterns, but it does not directly reduce costs. It incurs additional S3 storage costs for the logs. While analysis can inform optimization, it is not a direct cost-saving action. The company already knows about underutilization during off-peak hours, so this action is not necessary to achieve the goal.
- ✓
Configure the Auto Scaling group to use a mixed instances policy with a percentage of On-Demand and Spot Instances.
Why this is correct
A mixed instances policy allows you to combine On-Demand and Spot Instances, providing cost savings from Spot while maintaining a baseline of On-Demand for reliability. This approach can reduce costs without sacrificing performance, as the Auto Scaling group can maintain a minimum On-Demand capacity and use Spot for additional scalable capacity. It is a best practice for cost optimization in Auto Scaling groups.
- ✗
Use Spot Instances for all EC2 instances in the Auto Scaling group.
Why it's wrong here
Spot Instances can reduce costs, but they are not suitable for all instances in a web application that must maintain high availability. Spot Instances can be interrupted, which could cause service disruptions during peak hours. While they can be used for a portion of the capacity, using them for all instances is risky and could affect performance. The scenario requires no performance impact, so Spot for all is not appropriate.
- ✓
Implement scheduled scaling for the Auto Scaling group to reduce capacity during off-peak hours.
Why this is correct
Scheduled scaling allows you to adjust the desired capacity of the Auto Scaling group based on predictable traffic patterns. By scaling down during off-peak hours, you reduce the number of running EC2 instances, thereby lowering compute costs. This action directly addresses underutilization and does not affect performance during peak hours, as capacity is scaled back up in advance of peak traffic.
- ✗
Reduce the size of the ALB to a smaller load balancer type.
Why it's wrong here
Application Load Balancers do not have size options; they automatically scale with traffic. There is no smaller ALB type. This action is not possible and does not address the underutilized EC2 instances. The cost of the ALB is based on capacity units and is not the primary cost driver here. The focus should be on optimizing EC2 capacity.
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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.