SOA-C02 Cost and Performance Optimization Practice Question
A company runs a batch processing job on Amazon EC2 instances that runs for 3 hours each night. The job can be interrupted and can resume from the last checkpoint without data loss. The SysOps administrator wants to minimize compute costs for this workload. Which Amazon EC2 purchasing option should be used?
⚠ Common exam trap
A common mix-up: candidates choose On-Demand or Reserved Instances because they assume a nightly 3-hour job requires guaranteed availability, overlooking that Spot Instances are ideal for fault-tolerant, interruptible workloads and offer the lowest cost.
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
✓
Spot Instances
Spot Instances are correct because the batch job is fault-tolerant (can be interrupted and resume from checkpoints) and runs for a fixed 3-hour window nightly. Spot Instances offer significant cost savings (up to 90% off On-Demand) by using spare EC2 capacity, which can be reclaimed by AWS with a 2-minute interruption notice. Since the workload can handle interruptions gracefully, Spot Instances minimize compute costs while meeting the job's requirements.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
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On-Demand Instances
Why it's wrong here
On-Demand Instances carry the highest per-hour cost because there is no commitment or capacity discount, and that premium is especially wasteful for a job that runs only 3 hours nightly. Since the batch workflow already supports interruption handling via checkpointing, using On-Demand forces the company to pay full price while giving up the 60-90% savings that a Spot-based design could provide.
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Reserved Instances
Why it's wrong here
Reserved Instances are a 1- or 3-year contract that requires paying for capacity regardless of actual usage, making them economically justified only for workloads that run continuously or near-continuously. A nightly 3-hour batch job uses EC2 for slightly more than 12% of the day; a Standard RI would still be billed hourly for every day of the term, and even Convertible RIs offer only modest discounts for this sporadic usage pattern. This makes Reserved Instances a poor fit for such a short-duration, scheduled workload.
- ✓
Spot Instances
Why this is correct
Spot Instances give the company the largest possible EC2 discount, up to 90% off On-Demand, and are ideal for fault-tolerant, interruptible workloads like the described batch job. Because the job uses checkpointing, it can safely stop after a two-minute Spot interruption notice and later resume from the last saved state, so cost savings are maximized without sacrificing data integrity or job completion.
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Dedicated Hosts
Why it's wrong here
Dedicated Hosts are physical servers reserved for one customer, billed per host per hour, and are typically chosen to meet licensing or compliance requirements, not to reduce cost. A nightly EC2 batch job has no such need for a dedicated physical server, so this option is both significantly more expensive and administratively heavier than simply using a Spot capacity pool.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.