SAA-C03 Design High-Performing Architectures Practice Question
A company runs a web application on Amazon EC2 instances behind an Application Load Balancer (ALB). The application experiences variable traffic patterns, with sudden spikes during marketing campaigns. The operations team wants to ensure that the application can scale out quickly to handle the spikes and scale in when traffic decreases, while minimizing costs. Which solution should a solutions architect recommend?
⚠ Common exam trap
The trap here is assuming that scheduled scaling is always sufficient for variable traffic, when in fact unpredictable spikes require dynamic scaling policies.
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 a target tracking scaling policy based on average CPU utilization.
A target tracking scaling policy with an Auto Scaling group is the most effective way to handle variable traffic. It automatically adjusts capacity based on CPU utilization, scaling out during spikes and scaling in during low traffic, which optimizes both performance and cost. Other options are either static, do not address scaling, or require major architectural changes.
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 a target tracking scaling policy based on average CPU utilization.
Why this is correct
A target tracking scaling policy automatically adjusts the number of instances to maintain a specified metric, such as average CPU utilization, at a target value. This is ideal for variable traffic because it scales out when CPU rises and scales in when it falls. It helps handle sudden spikes and reduces costs during low traffic by terminating unnecessary instances.
- ✗
Deploy the application on AWS Lambda behind an API Gateway and remove the EC2 instances.
Why it's wrong here
Moving to a serverless architecture with Lambda and API Gateway can provide automatic scaling, but it requires significant application changes and may not be suitable for all workloads. The scenario describes an existing web application on EC2; refactoring to Lambda is not a quick or cost-effective solution for the immediate requirement. It also may not support the same features or performance characteristics.
- ✗
Use a scheduled scaling policy that adds instances at the start of each marketing campaign.
Why it's wrong here
Scheduled scaling is effective for predictable traffic patterns, but marketing campaigns may be unpredictable or occur at irregular intervals. This approach could lead to insufficient capacity if traffic spikes unexpectedly or unnecessary costs if the schedule does not match actual demand. It does not provide dynamic scaling based on real-time load.
- ✗
Enable sticky sessions on the ALB and increase the instance size.
Why it's wrong here
Sticky sessions ensure that a user's requests are routed to the same instance, which can help with session state but does not improve the ability to scale out. Increasing instance size (vertical scaling) is limited and does not handle sudden spikes efficiently. It also does not help scale in to reduce costs when traffic decreases.
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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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