SOA-C02 Spot Instances Practice Question
A company runs a batch processing application on Amazon EC2 instances that runs every night for 2 hours. The job can be interrupted and resumed without any issue. The SysOps administrator wants to minimize compute costs for this workload. Which EC2 purchasing option should be used?
⚠ Common exam trap
Watch out — candidates often choose Reserved Instances (Option C) thinking they always save money, but they fail to recognize that Reserved Instances are only cost-effective for steady-state, always-on workloads, not for short, interruptible batch jobs where Spot Instances provide greater savings without long-term commitment.
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 the correct choice because the workload is fault-tolerant (can be interrupted and resumed) and runs for only 2 hours nightly. Spot Instances offer significant cost savings (up to 90% off On-Demand) but can be reclaimed by AWS with a 2-minute warning, which is acceptable here since the job can resume without issue. This aligns with the goal of minimizing compute costs for a non-critical, interruptible batch process.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Spot Instances
Why this is correct
Spot Instances offer spare EC2 capacity at discounts of up to 90% compared to On-Demand, making them ideal for fault-tolerant, interruptible workloads like a nightly 2-hour batch job. If Spot capacity is reclaimed, the job can simply be restarted on another Spot Instance, and the short run duration minimizes disruption risk. The significant cost savings together with the workload's natural resilience to interruption make Spot the most cost-effective choice.
- ✗
On-Demand Instances
Why it's wrong here
On-Demand Instances provide full control, no upfront commitment, and are billed per second, but they carry the full list price without any discount. For a predictable nightly batch job running only 2 hours, you would pay for exactly those hours at standard rates every night, accumulating substantial cost over time. Since the task is short and interruptible, You would be overspending compared to Spot, which offers the same compute capability for a fraction of the price.
- ✗
Reserved Instances
Why it's wrong here
Reserved Instances require a 1-year or 3-year commitment and an upfront payment (or higher hourly rate with no upfront), designed for steady-state, always-on workloads that use capacity 24/7. A batch job that runs only 2 hours per night would leave the reserved capacity idle for 22 hours each day, wasting the majority of the capacity you paid for. Furthermore, the flexibility to change instance types is limited, making this option both financially inefficient and operationally rigid for such intermittent usage.
- ✗
Dedicated Hosts
Why it's wrong here
Dedicated Hosts provide a physical server fully dedicated to your use, which is necessary for meeting certain software licensing or compliance requirements, but they come at a premium price and carry the highest operational overhead. For a simple batch processing job, you gain no real benefit from such isolation, and you would be paying for the entire physical host even though the workload only utilizes a fraction of its capacity for a few hours nightly. This makes Dedicated Hosts the most expensive and least appropriate option for this scenario.
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Same concept, more angles
2 more ways this is tested on SOA-C02
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company runs a batch processing application on Amazon EC2 instances every night. The job takes exactly 1 hour to complete and is time-sensitive. The SysOps administrator wants to minimize compute costs while ensuring the job can be interrupted and resumed if needed. Which EC2 purchasing option is most cost-effective?
medium- A.On-Demand Instances
- B.Reserved Instances (Standard 1-year)
- ✓ C.Spot Instances
- D.Dedicated Hosts
Why C: Spot Instances are the most cost-effective option because the batch job is fault-tolerant (can be interrupted and resumed) and runs for exactly 1 hour nightly. Spot Instances offer up to 90% discount compared to On-Demand, and with the ability to handle interruptions via checkpointing, they meet the requirement for cost minimization while supporting resumption.
Variation 2. A company runs a batch processing application on Amazon EC2 that runs for 2 hours every night. The workload can tolerate interruptions. Which EC2 purchasing option provides the lowest cost for this use case?
easy- A.On-Demand Instances
- B.Reserved Instances
- ✓ C.Spot Instances
- D.Dedicated Hosts
Why C: Spot Instances are the correct choice because the workload is fault-tolerant, runs for a fixed 2-hour window nightly, and can tolerate interruptions. Spot Instances offer significant cost savings (up to 90% off On-Demand) by using spare EC2 capacity, which aligns perfectly with a batch job that can be retried if interrupted.
JA
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.