SAA-C03 Design Cost-Optimized Architectures Practice Question
CloudWatch metrics show your EC2 instances have average CPU utilization around 10% with stable performance over several weeks. The application does not require additional headroom right now. What is the most effective cost-optimization action?
⚠ Common exam trap
Many exam-takers think increasing capacity (Option B) or switching to Spot Instances (Option C) is always cost-effective, but they fail to recognize that right-sizing is the foundational first step before scaling or using Spot, especially when current utilization is low and stable.
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
✓
Right-size the instances to a smaller size that matches the observed utilization
Right-sizing EC2 instances to match observed utilization is the most effective cost-optimization action because the current instances are over-provisioned (average CPU at 10%). By selecting a smaller instance type that aligns with the actual workload, you reduce hourly costs without impacting performance, as the application has stable behavior and no need for headroom.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Right-size the instances to a smaller size that matches the observed utilization
Why this is correct
Right sizing reduces cost by matching instance capacity to actual demand. If average CPU is consistently low (around 10%) and performance is stable, it strongly indicates overprovisioning. Moving to a smaller instance (or a smaller capability within the same family) typically lowers hourly cost while maintaining sufficient capacity for the workload.
- ✗
Increase the Auto Scaling desired capacity to add more instances
Why it's wrong here
Adding more instances increases total compute capacity and typically increases cost, even if CPU utilization is low. Auto Scaling is intended to respond to demand changes; raising desired capacity without a demand need does not address the current overprovisioning.
When this WOULD be correct
This option would be correct if the application is experiencing high CPU utilization and performance degradation, and the goal is to improve performance or ensure high availability by distributing load across more instances.
- ✗
Switch to Spot Instances immediately even though interruptions would impact users
Why it's wrong here
Switching to Spot is a pricing decision that introduces interruption risk. The scenario’s primary measurable issue is persistent underutilization; switching to Spot would be unnecessary and potentially risky given the stated interruption impact. Cost optimization here should first target the dominant cost lever: oversized compute.
When this WOULD be correct
A question where the application is fault-tolerant, can handle interruptions gracefully (e.g., using Spot Instance best practices like checkpointing), and cost reduction is the primary goal, with no requirement for stable performance or minimal user impact.
- ✗
Disable detailed monitoring to reduce CPU usage from the monitoring agent
Why it's wrong here
Reducing monitoring detail might lower monitoring charges, but it does not address the main driver of EC2 cost: unused instance capacity. Any CPU impact from monitoring is usually minor compared with the savings from downsizing instances.
When this WOULD be correct
A scenario where the question asks: 'Your EC2 instances are running a batch job that is not performance-sensitive, and you want to reduce CloudWatch costs without affecting application performance. What should you do?' In that case, disabling detailed monitoring (switching to basic monitoring) would be correct to save on monitoring fees.
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.
✓Right-size the instances to a smaller size that matches the observed utilizationCorrect answer▾
Why this is correct
Right sizing reduces cost by matching instance capacity to actual demand. If average CPU is consistently low (around 10%) and performance is stable, it strongly indicates overprovisioning. Moving to a smaller instance (or a smaller capability within the same family) typically lowers hourly cost while maintaining sufficient capacity for the workload.
✗Increase the Auto Scaling desired capacity to add more instancesWrong answer — click to see why▾
Why this is wrong here
Increasing Auto Scaling desired capacity adds more instances, which increases cost without addressing the existing over-provisioning. The question states CPU utilization is low and stable, so adding instances would waste resources.
★ When this WOULD be the correct answer
This option would be correct if the application is experiencing high CPU utilization and performance degradation, and the goal is to improve performance or ensure high availability by distributing load across more instances.
Why candidates choose this
Candidates may think adding instances is always good for performance or cost optimization, or they confuse Auto Scaling with right-sizing, not realizing that adding instances increases cost when existing instances are underutilized.
✗Switch to Spot Instances immediately even though interruptions would impact usersWrong answer — click to see why▾
Why this is wrong here
Switching to Spot Instances immediately would risk interruptions that impact users, which is unacceptable for a production application requiring stable performance. The question states the application does not require additional headroom, but it does not indicate tolerance for interruptions.
★ When this WOULD be the correct answer
A question where the application is fault-tolerant, can handle interruptions gracefully (e.g., using Spot Instance best practices like checkpointing), and cost reduction is the primary goal, with no requirement for stable performance or minimal user impact.
Why candidates choose this
Candidates know Spot Instances are cheaper and may assume any cost-saving measure is good, overlooking the critical requirement of stable performance and user impact from interruptions.
✗Disable detailed monitoring to reduce CPU usage from the monitoring agentWrong answer — click to see why▾
Why this is wrong here
Disabling detailed monitoring does not reduce CPU usage from the monitoring agent; it only reduces the frequency of metric data sent to CloudWatch, which has negligible impact on CPU. The question focuses on cost optimization, and detailed monitoring costs extra, but the primary issue is that the instances are over-provisioned, not that monitoring costs are significant.
★ When this WOULD be the correct answer
A scenario where the question asks: 'Your EC2 instances are running a batch job that is not performance-sensitive, and you want to reduce CloudWatch costs without affecting application performance. What should you do?' In that case, disabling detailed monitoring (switching to basic monitoring) would be correct to save on monitoring fees.
Why candidates choose this
Candidates may think that disabling detailed monitoring reduces CPU overhead from the CloudWatch agent, thereby lowering utilization and costs. They might also confuse the cost of monitoring with compute costs, or believe that any reduction in monitoring activity directly saves significant money.
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?”
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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.