SOA-C02 Cost and Performance Optimization Practice Question
A company runs a web application on a fleet of Amazon EC2 instances that operate 24/7 with a steady and predictable load. The SysOps administrator wants to minimize compute costs while ensuring the required capacity is always available. Which EC2 purchasing option should the administrator use?
⚠ Common exam trap
Test-takers frequently choose Spot Instances for any cost-saving scenario, forgetting that Spot Instances can be terminated at any time, making them unsuitable for steady, predictable workloads that require constant availability.
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
Reserved Instances (RIs) are the correct choice because the workload runs 24/7 with steady, predictable load. RIs provide a significant discount (up to 72%) over On-Demand pricing in exchange for a one- or three-year commitment, ensuring cost minimization while guaranteeing capacity availability in the specified Availability Zone.
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
Why this is correct
Reserved Instances are the most cost-effective choice for a fleet of EC2 instances running a production web application that operates continuously. By committing to 1- or 3-year terms, you can save up to 72% compared to On-Demand pricing, with Flexible size benefits and the ability to change Availability Zones or instance sizes within the same family. Payment options (All Upfront, Partial Upfront, No Upfront) let you further optimize cost based on cash flow, and unused compute capacity is applied automatically. For an always-on workload, the upfront commitment is justified by the substantial savings.
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Spot Instances
Why it's wrong here
Spot Instances offer discounts of up to 90% compared to On-Demand but rely on excess EC2 capacity that AWS can reclaim at any time with a two-minute warning. The web application is always-on and stateful sessions or front-end traffic cannot tolerate interruptions; if spot capacity is reclaimed, the fleet loses instances and availability drops. Even with Spot Fleet or capacity-rebalance recommendations, the risk of instance termination makes Spot unsuitable for serving live production traffic without a fault-tolerant, stateless architecture that the scenario doesn't specify.
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On-Demand Instances
Why it's wrong here
On-Demand instances have no upfront commitment and use per-second billing, making them ideal for short-term or unpredictable workloads; however, for a 24/7 web application they carry a premium price that can be up to 70% higher than Reserved/Spot pricing. Since the workload is steady-state with no need for rapid scaling or burst capacity, paying the full on-demand rate is wasteful. The business would be leaving significant savings on the table by not committing to Reserved Instances for the baseline capacity.
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Dedicated Hosts
Why it's wrong here
Dedicated Hosts provide a physical EC2 server solely for your use, which is necessary for licensing models that require dedicated CPU or for compliance mandates like HIPAA or SAP, but they cost significantly more than standard Reserved Instances. The scenario mentions a plain web application on EC2 with no mention of software licensing tied to sockets/physical cores or multi-tenant compliance requirements. Therefore, choosing a Dedicated Host adds extra cost without delivering any functional benefit for this workload, making Reserved Instances the superior economical choice.
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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.