- A
Use a mixed instances policy and set the 'On-Demand Base' capacity to the minimum number of instances required during business hours, and 'On-Demand percentage above base' to 0% so that any additional capacity is Spot.
This ensures at least the baseline number of On-Demand instances always run, meeting the availability requirement. Any extra capacity uses Spot Instances for cost savings.
- B
Use a launch template that specifies a Spot Instance type and set the total capacity to the desired level, relying on capacity rebalance to replace interrupted Spot Instances.
Why wrong: If all instances are Spot, the baseline capacity is not guaranteed because Spot Instances can be reclaimed at any time. Capacity rebalance helps but does not ensure capacity.
- C
Purchase Compute Savings Plans to cover the entire Auto Scaling group, and use only Spot Instances for all capacity.
Why wrong: Savings Plans provide a discount but do not guarantee capacity. Spot Instances still risk interruption, so baseline capacity is not assured.
- D
Configure the Auto Scaling group with a launch template that sets the instance market to 'spot' and use a scaling policy that always maintains the minimum capacity.
Why wrong: Even with a scaling policy, Spot Instances can be terminated by EC2, causing the group to fall below the minimum if replacements are delayed or unavailable.
Quick Answer
The correct answer is to use a mixed instances policy with the On-Demand Base capacity set to the minimum number of instances required during business hours and the On-Demand percentage above base set to 0%. This works because the On-Demand Base acts as a hard floor for capacity that is immune to Spot interruptions, guaranteeing your baseline workload always runs on reliable On-Demand instances. Setting the percentage above base to 0% then directs all additional, non-baseline capacity to Spot Instances, maximizing cost savings while maintaining the required capacity floor. On the SOA-C02 exam, this scenario tests your understanding of how mixed instances policies decouple baseline reliability from elastic scaling—a common trap is confusing the On-Demand Base with a percentage or forgetting that Spot Instances can be reclaimed, which would break the baseline if used there. Memory tip: think of the On-Demand Base as your “non-negotiable floor” and the percentage above base as your “cost-saving ceiling.”
SOA-C02 Cost and Performance Optimization Practice Question
This SOA-C02 practice question tests your understanding of cost and performance optimization. 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.
A company runs a web application on Amazon EC2 instances in an Auto Scaling group. The application experiences steady traffic during business hours and very low traffic overnight. The SysOps administrator wants to optimize costs by using a mix of On-Demand and Spot Instances. The administrator also requires that the total capacity never falls below the baseline level needed during business hours, even if Spot Instances are reclaimed. Which combination of Auto Scaling features should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"never"Why it matters: Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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
Use a mixed instances policy and set the 'On-Demand Base' capacity to the minimum number of instances required during business hours, and 'On-Demand percentage above base' to 0% so that any additional capacity is Spot.
Option A is correct because a mixed instances policy allows the Auto Scaling group to use both On-Demand and Spot Instances. By setting the 'On-Demand Base' capacity to the minimum number of instances required during business hours, you guarantee that baseline capacity is always fulfilled by On-Demand Instances, which are not subject to interruption. Setting 'On-Demand percentage above base' to 0% ensures that any additional capacity beyond the base is fulfilled by Spot Instances, optimizing cost while maintaining the required capacity floor.
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 a mixed instances policy and set the 'On-Demand Base' capacity to the minimum number of instances required during business hours, and 'On-Demand percentage above base' to 0% so that any additional capacity is Spot.
Why this is correct
This ensures at least the baseline number of On-Demand instances always run, meeting the availability requirement. Any extra capacity uses Spot Instances for cost savings.
Clue confirmation
The clue word "never" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a launch template that specifies a Spot Instance type and set the total capacity to the desired level, relying on capacity rebalance to replace interrupted Spot Instances.
Why it's wrong here
If all instances are Spot, the baseline capacity is not guaranteed because Spot Instances can be reclaimed at any time. Capacity rebalance helps but does not ensure capacity.
- ✗
Purchase Compute Savings Plans to cover the entire Auto Scaling group, and use only Spot Instances for all capacity.
Why it's wrong here
Savings Plans provide a discount but do not guarantee capacity. Spot Instances still risk interruption, so baseline capacity is not assured.
- ✗
Configure the Auto Scaling group with a launch template that sets the instance market to 'spot' and use a scaling policy that always maintains the minimum capacity.
Why it's wrong here
Even with a scaling policy, Spot Instances can be terminated by EC2, causing the group to fall below the minimum if replacements are delayed or unavailable.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume that using Spot Instances with a scaling policy or capacity rebalance alone can guarantee capacity, but they fail to recognize that only On-Demand Instances provide a hard guarantee against interruption, which is why the mixed instances policy with an explicit On-Demand base is required.
Detailed technical explanation
How to think about this question
The mixed instances policy in Auto Scaling groups uses the 'On-Demand Base' parameter to specify a fixed number of On-Demand Instances that are launched first, ensuring a stable capacity floor. The 'On-Demand percentage above base' parameter then determines the proportion of additional capacity that is On-Demand versus Spot, with 0% meaning all extra capacity is Spot. This approach leverages the Spot Instance interruption notice (which provides a 2-minute warning) to gracefully handle reclaims, but the baseline On-Demand capacity remains unaffected, providing a cost-optimized yet resilient architecture.
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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Cost and Performance Optimization — study guide chapter
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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: Use a mixed instances policy and set the 'On-Demand Base' capacity to the minimum number of instances required during business hours, and 'On-Demand percentage above base' to 0% so that any additional capacity is Spot. — Option A is correct because a mixed instances policy allows the Auto Scaling group to use both On-Demand and Spot Instances. By setting the 'On-Demand Base' capacity to the minimum number of instances required during business hours, you guarantee that baseline capacity is always fulfilled by On-Demand Instances, which are not subject to interruption. Setting 'On-Demand percentage above base' to 0% ensures that any additional capacity beyond the base is fulfilled by Spot Instances, optimizing cost while maintaining the required capacity floor.
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.
Are there clue words in this question I should notice?
Yes — watch for: "never". Absolute qualifier. True only if the statement has zero exceptions — be cautious of options that seem obvious but break down in edge cases.
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
This SOA-C02 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 SOA-C02 exam.
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