← SOA-C02·Amazon Web Services

Question 640 of 1,546

Cost and Performance Optimization →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is to modify the existing Reserved Instance to a smaller instance size, such as from m5.large to t3.medium, and then use Auto Scaling with a scheduled scaling action to start and stop the instance during business hours. This approach directly addresses the underutilization because a Standard RI’s attributes—like instance size and scope—can be modified once during its term, allowing you to align the reservation with the actual 4-hour daily usage pattern. On the AWS Certified SysOps Administrator SOA-C02 exam, this scenario tests your understanding of how to optimize utilization of Reserved Instances without losing the upfront investment; a common trap is thinking you can simply stop the instance to save costs, but a stopped instance still wastes the RI benefit since it cannot be applied to a non-running resource. Another pitfall is selling the RI on the Marketplace, which forfeits the upfront payment. Remember the memory tip: “Modify, don’t stop—match the size to the time.”

SOA-C02 Cost and Performance Optimization Practice Question

This SOA-C02 practice question tests your understanding of cost and performance optimization. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

A SysOps administrator is investigating a cost increase in a production AWS account. They notice that an EC2 instance with a Reservation has been running continuously for months. The instance type is m5.large in us-east-1. The administrator sees that the instance is using a Standard Reserved Instance (RI) that was purchased 6 months ago for a 1-year term. However, the current utilization shows that the instance is only used for 4 hours per day. What should the administrator do to optimize costs without affecting availability?

Question 1hardmultiple choice

Full question →

A
Stop the instance during off-hours using Instance Scheduler, but keep the RI as-is.
Why wrong: RI benefit applies to running instances; stopping the instance wastes the RI payment for those hours.
B
Sell the current RI on the Reserved Instance Marketplace and purchase a new Convertible RI for a smaller instance type.
Why wrong: Selling the RI may incur loss and does not optimize the current usage pattern.
C
Modify the existing RI to a smaller instance size (e.g., m5.large to m5.xlarge? no, smaller: e.g., t3.medium) and use Auto Scaling with a schedule to start/stop the instance during business hours.
Modifying RI to a smaller size matches usage; scheduled stop reduces running hours.
D
Convert the RI to a Convertible RI and exchange it for a larger instance family to get more compute per hour.
Why wrong: Larger instance would increase cost, not decrease.

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

✓

Modify the existing RI to a smaller instance size (e.g., m5.large to m5.xlarge? no, smaller: e.g., t3.medium) and use Auto Scaling with a schedule to start/stop the instance during business hours.

Option B is correct because modifying the RI to a smaller size can better match the usage pattern, and using Auto Scaling with a scheduled scaling puts the instance to sleep when not needed. Option A is wrong because selling on the Reserved Instance Marketplace would lose the upfront payment and not address the over-provisioning. Option C is wrong because converting to On-Demand is more expensive for the hours used. Option D is wrong because simply stopping the instance during off-hours does not change the RI benefit; the RI will still be applied to the stopped instance (though RI cannot be applied to stopped instances; it would be wasted).

Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
Stop the instance during off-hours using Instance Scheduler, but keep the RI as-is.
Why it's wrong here
RI benefit applies to running instances; stopping the instance wastes the RI payment for those hours.
✗
Sell the current RI on the Reserved Instance Marketplace and purchase a new Convertible RI for a smaller instance type.
Why it's wrong here
Selling the RI may incur loss and does not optimize the current usage pattern.
✓
Modify the existing RI to a smaller instance size (e.g., m5.large to m5.xlarge? no, smaller: e.g., t3.medium) and use Auto Scaling with a schedule to start/stop the instance during business hours.
Why this is correct
Modifying RI to a smaller size matches usage; scheduled stop reduces running hours.
Related concept
Static NAT maps one inside address to one outside address.
✗
Convert the RI to a Convertible RI and exchange it for a larger instance family to get more compute per hour.
Why it's wrong here
Larger instance would increase cost, not decrease.

Common exam traps

Common exam trap: NAT rules depend on direction and matching traffic

NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.

Detailed technical explanation

How to think about this question

NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.

KKey Concepts to Remember

Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.

TExam Day Tips

Identify inside and outside interfaces first.
Check whether the scenario needs static NAT, dynamic NAT or PAT.
Do not confuse NAT matching ACLs with normal packet-filtering intent.

Key takeaway

NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.

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.

Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.

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FAQ

Questions learners often ask

What does this SOA-C02 question test?

Cost and Performance Optimization — This question tests Cost and Performance Optimization — Static NAT maps one inside address to one outside address..

What is the correct answer to this question?

The correct answer is: Modify the existing RI to a smaller instance size (e.g., m5.large to m5.xlarge? no, smaller: e.g., t3.medium) and use Auto Scaling with a schedule to start/stop the instance during business hours. — Option B is correct because modifying the RI to a smaller size can better match the usage pattern, and using Auto Scaling with a scheduled scaling puts the instance to sleep when not needed. Option A is wrong because selling on the Reserved Instance Marketplace would lose the upfront payment and not address the over-provisioning. Option C is wrong because converting to On-Demand is more expensive for the hours used. Option D is wrong because simply stopping the instance during off-hours does not change the RI benefit; the RI will still be applied to the stopped instance (though RI cannot be applied to stopped instances; it would be wasted).

What should I do if I get this SOA-C02 question wrong?

What is the key concept behind this question?

Static NAT maps one inside address to one outside address.

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