- A
Right-size the instances to a smaller size that matches the observed utilization
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.
- B
Increase the Auto Scaling desired capacity to add more instances
Why wrong: 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.
- C
Switch to Spot Instances immediately even though interruptions would impact users
Why wrong: 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.
- D
Disable detailed monitoring to reduce CPU usage from the monitoring agent
Why wrong: 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.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
- ✗
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.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may 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.
Trap categories for this question
Scenario analysis trap
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.
Detailed technical explanation
How to think about this question
Right-sizing involves analyzing CloudWatch metrics (e.g., CPUUtilization, NetworkIn/Out, DiskReadOps) over a representative period (e.g., 2 weeks) to select an instance family/size that meets peak demands without waste. AWS Compute Optimizer or Trusted Advisor can automate this by comparing utilization percentiles (e.g., P95 CPU) against instance specifications. In practice, a t3.small (2 vCPU, 2 GiB RAM) might replace an m5.large (2 vCPU, 8 GiB RAM) if memory and network are also underutilized, leveraging burstable credits for occasional spikes.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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