SOA-C02 Cost and Performance Optimization Practice Question
A company runs a batch processing job every night on Amazon EC2 instances. The job takes exactly 2 hours to complete and can be interrupted and resumed later. The SysOps administrator wants to minimize compute costs. Which purchasing option should be used?
⚠ Common exam trap
Many candidates choose On-Demand Instances due to a mistaken belief that any interruptible workload requires guaranteed availability, ignoring that Spot Instances are explicitly designed for fault-tolerant, stateless, or checkpointable workloads like batch processing.
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 batch job is fault-tolerant (can be interrupted and resumed) and runs for a fixed 2-hour window nightly. Spot Instances offer up to 90% cost savings compared to On-Demand, and with the ability to handle interruptions via checkpointing, they minimize compute costs without requiring a long-term commitment.
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 deliver up to a 90% discount compared to On-Demand pricing because AWS sells spare EC2 capacity through a bidding market. Nightly batch jobs that can be interrupted and restarted or resumed are textbook use cases for Spot, especially with the EC2 Fleet or Spot Fleet using a capacity-optimized allocation strategy. To tolerate eviction, you can implement checkpointing in the job and set short max-price per instance-hour, letting AWS reclaim the instance mid-run without corrupting output. The ability to tolerate interruption is precisely why Spot minimizes costs over all other options for this flexible, interruptible workload.
- ✗
Reserved Instances
Why it's wrong here
Reserved Instances are meant for steady-state, predictable, always-on workloads and require a 1- or 3-year commitment to earn their discount. A nightly batch job that runs for a few hours uses that reserved capacity for only a small fraction of the day, yet you still pay for the instance around the clock, so the effective per-usage-hour cost is far higher than Spot. While they beat On-Demand pricing for continuous usage, they are not the most economical option here because you would pay for idle capacity. The long-term lock-in also reduces the flexibility to change instance types or family as the batch job evolves.
- ✗
On-Demand Instances
Why it's wrong here
On-Demand Instances charge the full per-second or per-hour list price with no upfront commitment or volume discount, making them the highest-cost option for a workload that runs predictably every night. The value of On-Demand is that you can launch and stop instances at any time with zero long-term obligation, but this flexibility provides no financial benefit for a batch job whose schedule is fixed and whose interruptions are acceptable. Since you can precisely predict the nightly run window, paying On-Demand rates means leaving significant savings on the table. Cost-minimization best practices explicitly recommend reserved or Spot pricing for predictable, interruptible workloads, not full-price On-Demand.
- ✗
Dedicated Instances
Why it's wrong here
Dedicated Instances run on physical servers exclusively for your account, billing you an additional per-hour fee ($10 per region per hour for dedicated tenancy) on top of the regular instance rate. They are only justified when your compliance, regulatory, or licensing requirements demand single-tenant isolation or physical server control. A standard nightly batch job does not need dedicated hardware, so using Dedicated Instances would actually increase costs—often beyond even On-Demand pricing—and provide no processing benefit. Thus, despite their billing being predictable, they are the least cost-efficient choice for this workload.
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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.