The answer is to use Spot Instances for the core and task nodes and an On-Demand instance for the primary node. This is the most cost-effective approach because Spot Instances can reduce compute costs by up to 90% compared to On-Demand, making them ideal for fault-tolerant batch processing workloads like EMR. The key technical concept here is that the primary node manages the cluster and must remain stable, so it requires an On-Demand instance to avoid disruption, while core and task nodes can handle interruptions gracefully and be replaced. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your understanding of EMR cost optimization using Spot Instances for batch processing, often appearing as a trap where candidates mistakenly choose Reserved Instances for a short nightly job or assume all nodes should be Spot. Remember the memory tip: "Primary stays steady, the rest get spotty."
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 batch processing job on Amazon EMR every night. The job runs for 6 hours and requires a cluster of 20 m5.xlarge instances. The company wants to reduce costs while ensuring the job completes on time. Which solution is MOST cost-effective?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Spot Instances for core and task nodes and an On-Demand instance for the primary node.
Using Spot Instances for the core and task nodes can significantly reduce costs, as Spot Instances are often much cheaper than On-Demand. The primary node should be On-Demand to avoid disruption. Using all On-Demand is more expensive. Reserved Instances are for steady-state workloads, not short-term jobs. Instance fleets can mix instance types but do not inherently reduce costs like Spot.
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 for all nodes.
Why it's wrong here
On-Demand is more expensive than Spot.
✗
Purchase Reserved Instances for the entire cluster.
Why it's wrong here
Reserved Instances are not cost-effective for a 6-hour nightly job.
✓
Use Spot Instances for core and task nodes and an On-Demand instance for the primary node.
Why this is correct
This significantly reduces cost while maintaining reliability.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use Spot Instances for the primary node and On-Demand for core and task nodes.
Why it's wrong here
The primary node should be On-Demand to avoid disruption.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→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 SOA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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 Spot Instances for core and task nodes and an On-Demand instance for the primary node. — Using Spot Instances for the core and task nodes can significantly reduce costs, as Spot Instances are often much cheaper than On-Demand. The primary node should be On-Demand to avoid disruption. Using all On-Demand is more expensive. Reserved Instances are for steady-state workloads, not short-term jobs. Instance fleets can mix instance types but do not inherently reduce costs like Spot.
What should I do if I get this SOA-C02 question wrong?
Identify which SOA-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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