- A
Use On-Demand instances only
Why wrong: On-Demand pricing offers no discount and is the most expensive option for a predictable workload. It does not take advantage of any cost-saving purchasing options.
- B
Purchase Reserved Instances for the baseline capacity and use Spot Instances for the additional capacity during peak hours
This approach minimizes costs by applying the highest discount (Reserved Instances) to the steady-state capacity and leveraging the cost savings of Spot Instances for the flexible, peak-demand capacity. Auto Scaling can be configured to launch Spot Instances as needed, providing both cost efficiency and performance.
- C
Increase the minimum number of instances in the Auto Scaling group
Why wrong: Increasing the minimum number of instances would keep more instances running during low-traffic periods, increasing costs unnecessarily without improving peak responsiveness.
- D
Use Dedicated Hosts to reduce licensing costs
Why wrong: Dedicated Hosts are primarily used for compliance or to reduce software licensing costs when using certain server-bound licenses. They are typically more expensive than shared tenancy and do not directly address compute cost optimization for a standard web application.
SOA-C02 Cost and Performance Optimization Practice Question
This SOA-C02 practice question tests your understanding of cost and performance optimization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 company runs a web application on a fleet of Amazon EC2 instances behind an Application Load Balancer. The application has predictable traffic patterns with high traffic during business hours and low traffic at night. The SysOps administrator wants to reduce compute costs while ensuring the application remains responsive during peak hours. The administrator has already implemented Auto Scaling based on CPU utilization. Which additional action should the administrator take to optimize costs?
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
Purchase Reserved Instances for the baseline capacity and use Spot Instances for the additional capacity during peak hours
Option B is correct because it combines Reserved Instances for predictable baseline capacity (lower cost per hour) with Spot Instances for elastic peak demand, leveraging Auto Scaling to handle variable traffic. This hybrid approach reduces compute costs compared to using On-Demand instances for all capacity, while maintaining responsiveness during peak hours.
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.
- ✗
Use On-Demand instances only
Why it's wrong here
On-Demand pricing offers no discount and is the most expensive option for a predictable workload. It does not take advantage of any cost-saving purchasing options.
- ✓
Purchase Reserved Instances for the baseline capacity and use Spot Instances for the additional capacity during peak hours
Why this is correct
This approach minimizes costs by applying the highest discount (Reserved Instances) to the steady-state capacity and leveraging the cost savings of Spot Instances for the flexible, peak-demand capacity. Auto Scaling can be configured to launch Spot Instances as needed, providing both cost efficiency and performance.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Increase the minimum number of instances in the Auto Scaling group
Why it's wrong here
Increasing the minimum number of instances would keep more instances running during low-traffic periods, increasing costs unnecessarily without improving peak responsiveness.
- ✗
Use Dedicated Hosts to reduce licensing costs
Why it's wrong here
Dedicated Hosts are primarily used for compliance or to reduce software licensing costs when using certain server-bound licenses. They are typically more expensive than shared tenancy and do not directly address compute cost optimization for a standard web application.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think increasing the minimum instance count (Option C) improves responsiveness, but it actually increases costs during low-traffic periods without addressing the cost optimization goal.
Detailed technical explanation
How to think about this question
Reserved Instances provide a significant discount (up to 72%) over On-Demand for a 1- or 3-year commitment, ideal for steady-state workloads. Spot Instances can be up to 90% cheaper but can be interrupted with a 2-minute warning, so they are suitable for fault-tolerant, stateless workloads like web application tiers. Auto Scaling groups can mix instance types and purchasing options via a mixed instances policy, allowing the administrator to define a percentage of On-Demand/Reserved for baseline and Spot for surplus.
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 SOA-C02 question test?
Cost and Performance Optimization — This question tests Cost and Performance Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Purchase Reserved Instances for the baseline capacity and use Spot Instances for the additional capacity during peak hours — Option B is correct because it combines Reserved Instances for predictable baseline capacity (lower cost per hour) with Spot Instances for elastic peak demand, leveraging Auto Scaling to handle variable traffic. This hybrid approach reduces compute costs compared to using On-Demand instances for all capacity, while maintaining responsiveness during peak hours.
What should I do if I get this SOA-C02 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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