SOA-C02 Cost and Performance Optimization Practice Question
A company runs a web application on Amazon EC2 instances that have variable traffic patterns. The application experiences steady baseline traffic with occasional spikes. The SysOps administrator wants to optimize costs while ensuring performance during spikes. Which pricing model should be used for the baseline capacity and for the burst capacity?
⚠ Common exam trap
Watch out — candidates often assume On-Demand is the only safe choice for baseline or that Spot Instances are too risky for any production use, but the question specifically allows for burst capacity that can tolerate interruptions, making Spot the optimal cost-saving choice.
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
✓
Reserved Instances for baseline, Spot Instances for burst capacity
Reserved Instances provide a significant discount (up to 72%) over On-Demand for steady-state workloads, making them ideal for baseline capacity. Spot Instances offer the lowest cost (up to 90% discount) but can be interrupted with a 2-minute warning, which is acceptable for burst capacity that can tolerate interruptions or be designed to failover gracefully. This combination minimizes cost while ensuring the baseline always runs and burst capacity can be added during spikes.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Reserved Instances for baseline, Spot Instances for burst capacity
Why this is correct
Reserved Instances (RIs) lock in a lower hourly rate (up to 72% off On-Demand) for a 1- or 3-year term, making them ideal for the steady, predictable baseline portion of the workload. Spot Instances, priced at up to 90% off On-Demand, provide cheap burst capacity that can be interrupted and replaced, which is acceptable for transient spikes. This combination minimizes cost while ensuring the always-on core stays reliable.
- ✗
On-Demand Instances for baseline, Reserved Instances for burst capacity
Why it's wrong here
Using On-Demand for the baseline wastes money because you pay the full list price for compute that runs continuously, when a Reserved Instance commitment would slash that cost. Applying RIs to burst capacity is counterproductive: bursts are intermittent and may not last long enough to justify a 1- or 3-year commitment, and you would be paying for capacity you often don't need. This mismatched strategy raises overall spending and reduces financial efficiency.
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Spot Instances for baseline, On-Demand Instances for burst capacity
Why it's wrong here
Spot pricing comes with a crucial caveat: AWS can reclaim the instance with a two-minute notification, causing abrupt termination that is unacceptable for a core baseline service. Burst capacity usually needs to be available immediately and reliably, and On-Demand does deliver that, but at a premium higher than either RIs or Spot. Putting the interruptible resource on the always-on component risks downtime and violates best practices for fault-tolerant design.
- ✗
Dedicated Hosts for baseline, Spot Instances for burst capacity
Why it's wrong here
Dedicated Hosts are single-tenant physical servers used to satisfy licensing restrictions or compliance requirements, and they come with a premium cost that far exceeds RIs for the same compute. Since the baseline workload is just a standard web app, it almost certainly doesn't need dedicated tenancy, so this choice adds unnecessary expense without any benefit. While the Spot burst half of the strategy is reasonable, the baseline half makes the overall design cost-inefficient and is rarely justified.
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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.