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Question 795 of 1,040

Design Cost-Optimized Architectures →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is to perform right-sizing by downsizing to a smaller instance family or size and then validating SLAs. This is correct because the workload shows sustained CPU utilization of only 6% with no memory pressure and queue latency already meeting all SLAs, which clearly indicates the current instance is over-provisioned. Right-sizing EC2 instances for cost optimization directly reduces compute spend without introducing risk, as performance requirements are already satisfied. On the SAA-C03 exam, this scenario tests your understanding of the AWS Well-Architected Cost Optimization pillar, specifically the principle of matching capacity to actual demand. A common trap is to suggest purchasing Savings Plans or Reserved Instances first—those lock in waste if the instance is oversized. Instead, always right-size before committing to discounts. Memory tip: “6% CPU? Downsize first, commit later.”

SAA-C03 Design Cost-Optimized Architectures Practice Question

This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.

An Auto Scaling group for a background worker runs EC2 instances continuously. Over the last 30 days, CloudWatch shows sustained CPU utilization around 6% with no memory pressure, and queue processing latency meets all SLAs. The team wants to lower monthly cost with minimal risk. What is the best next action?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

Question 1mediummultiple choice

Full question →

A
Increase the instance size to reduce CPU throttling risk
Why wrong: The metrics show sustained low CPU with no reported throttling risk. Increasing size would likely increase cost immediately without addressing an existing performance problem.
B
Perform right sizing by downsizing to a smaller instance family/size and validate SLAs
Right sizing uses actual utilization to remove overprovisioning. With low CPU and no memory pressure and SLAs already met, downsizing (while validating under load and during a controlled rollout) is the safest way to reduce waste.
C
Switch the group to Spot Instances to reduce cost without changing instance sizing
Why wrong: Spot could reduce compute price, but it introduces interruption risk and additional operational complexity. When the primary waste is clearly overprovisioned capacity, downsizing is the more direct and lower-risk cost optimization.
D
Buy Reserved Instances with a long term commitment before making any sizing changes
Why wrong: Purchasing capacity commitments can reduce unit price, but it does not fix the cost waste from running much larger-than-needed instances. Since the instance utilization indicates overprovisioning, right sizing should come first to maximize savings with minimal risk.

Full breakdown with real-world context →

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

✓

Perform right sizing by downsizing to a smaller instance family/size and validate SLAs

The current instance type is over-provisioned, as sustained CPU utilization is only 6% with no memory pressure and all SLAs are met. Right-sizing to a smaller instance family or size directly reduces compute cost while maintaining performance, making it the lowest-risk, cost-optimization action. This aligns with the AWS Well-Architected Framework's cost optimization pillar, which recommends matching instance capacity to actual workload requirements.

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.

✗
Increase the instance size to reduce CPU throttling risk
Why it's wrong here
The metrics show sustained low CPU with no reported throttling risk. Increasing size would likely increase cost immediately without addressing an existing performance problem.
✓
Perform right sizing by downsizing to a smaller instance family/size and validate SLAs
Why this is correct
Right sizing uses actual utilization to remove overprovisioning. With low CPU and no memory pressure and SLAs already met, downsizing (while validating under load and during a controlled rollout) is the safest way to reduce waste.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
Switch the group to Spot Instances to reduce cost without changing instance sizing
Why it's wrong here
Spot could reduce compute price, but it introduces interruption risk and additional operational complexity. When the primary waste is clearly overprovisioned capacity, downsizing is the more direct and lower-risk cost optimization.
✗
Buy Reserved Instances with a long term commitment before making any sizing changes
Why it's wrong here
Purchasing capacity commitments can reduce unit price, but it does not fix the cost waste from running much larger-than-needed instances. Since the instance utilization indicates overprovisioning, right sizing should come first to maximize savings with minimal risk.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates may assume Spot Instances are always the cheapest option, but they ignore the risk of interruption for a continuously running workload where SLAs must be met, making right-sizing the safer and more appropriate first step.

Trap categories for this question

Command / output trap
The metrics show sustained low CPU with no reported throttling risk. Increasing size would likely increase cost immediately without addressing an existing performance problem.

Detailed technical explanation

How to think about this question

Right-sizing involves analyzing CloudWatch metrics (e.g., CPUUtilization, MemoryUtilization) over a representative period (e.g., 14–30 days) to identify underutilized instances. AWS Compute Optimizer or a manual review of instance families (e.g., moving from a compute-optimized C5 to a general-purpose M5 or a smaller size like t3.medium) can reduce costs by 30–50% while maintaining performance. The key is to validate SLAs after the change, as smaller instances may have lower network throughput or EBS bandwidth that could impact queue processing latency.

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

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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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: Perform right sizing by downsizing to a smaller instance family/size and validate SLAs — The current instance type is over-provisioned, as sustained CPU utilization is only 6% with no memory pressure and all SLAs are met. Right-sizing to a smaller instance family or size directly reduces compute cost while maintaining performance, making it the lowest-risk, cost-optimization action. This aligns with the AWS Well-Architected Framework's cost optimization pillar, which recommends matching instance capacity to actual workload requirements.

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.

Are there clue words in this question I should notice?

Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Same concept, more angles

2 more ways this is tested on SAA-C03

These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.

Variation 1. A team runs an EC2-based API on a single Auto Scaling group (ASG). Over the last month, they observed: - Average CPU utilization is ~15%. - p95 latency is stable and within the performance target. - The attached EBS volumes are gp3, provisioned with high baseline IOPS/throughput “just to be safe,” but CloudWatch shows consistently low utilization of those provisioned IOPS/throughput limits. They want to reduce monthly cost while maintaining current performance. Which action is the best cost-optimized choice?

medium

A.Stop resizing EBS and only scale out the ASG during peak traffic, because changing EBS performance settings risks latency spikes.
✓ B.Right-size both the compute and the gp3 volumes: reduce the EC2 instance size (via the ASG launch template/desired capacity configuration) and update gp3 IOPS/throughput settings to match observed utilization while keeping p95 latency targets.
C.Switch the instances to EC2 Spot immediately, because Spot always lowers costs without adding operational risk or affecting performance.
D.Move the workload to a larger instance class and keep the gp3 settings unchanged to avoid operational tuning work.

Why B: Option B is correct because the workload is over-provisioned in both compute and storage. Average CPU is only 15%, so a smaller instance size can handle the load without affecting p95 latency. The gp3 volumes have high baseline IOPS/throughput that are never used, so reducing them to match actual utilization directly lowers costs without performance risk.

Variation 2. 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?

easy

✓ A.Right-size the instances to a smaller size that matches the observed utilization
B.Increase the Auto Scaling desired capacity to add more instances
C.Switch to Spot Instances immediately even though interruptions would impact users
D.Disable detailed monitoring to reduce CPU usage from the monitoring agent

Why A: 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.

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