SOA-C02 Cost and Performance Optimization Practice Question
A company runs a stateless web application on Amazon EC2 instances behind an Application Load Balancer. The application usage is consistent throughout the day and is expected to grow steadily over the next year. The SysOps administrator wants to minimize compute costs while ensuring capacity is available. Which purchasing option should the administrator use for the EC2 instances?
⚠ Common exam trap
Many candidates choose On-Demand Instances for simplicity, overlooking the significant cost savings of Reserved Instances for predictable, steady workloads, or they incorrectly choose Spot Instances without considering the interruption risk for a production application.
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 (Standard, 1-year or 3-year)
The application has a steady, predictable usage pattern and is expected to grow steadily, making Reserved Instances (Standard) the most cost-effective option. By committing to a 1-year or 3-year term, the administrator can receive a significant discount (up to 72% compared to On-Demand) while ensuring capacity is always available. This aligns with the requirement to minimize compute costs without sacrificing availability for a stateless, load-balanced workload.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
On-Demand Instances
Why it's wrong here
On-Demand Instances bill per second with no upfront commitment, making them flexible but at the highest hourly rate. For a workload that runs continuously around the clock, these costs rapidly exceed a Reserved Instance. On-Demand is best suited to short-term spikes or unpredictable workloads, not the steady, predictable baseline of a production web application.
- ✓
Reserved Instances (Standard, 1-year or 3-year)
Why this is correct
Standard Reserved Instances require a 1- or 3-year commitment to a specific instance family and Region, and optionally an Availability Zone. In exchange, AWS provides a significant hourly discount (up to roughly 72% compared to On-Demand) plus a capacity reservation when you specify an Availability Zone. This makes them the most cost-effective and dependable choice for a stateless web app that has a predictable, steady baseline load and must remain consistently available.
- ✗
Spot Instances
Why it's wrong here
Spot Instances run on spare EC2 capacity at discounts of up to 90%, but AWS can reclaim them with a two-minute interruption warning when capacity is needed elsewhere. While a stateless architecture can tolerate individual instance replacement, relying solely on Spot risks whole-fleet interruption and availability gaps for a customer-facing web application. Spot is designed for fault-tolerant batch jobs or transient workloads, not for a steady-state service that requires guaranteed uptime.
- ✗
Dedicated Hosts
Why it's wrong here
Dedicated Hosts provide a physical server dedicated to your use, allowing you to bring existing server-bound software licenses and satisfy compliance or regulatory requirements. Billing is per host, and hosts are typically more expensive than equivalent On-Demand or Reserved Instance usage, especially when running small instance sizes. Choosing Dedicated Hosts purely for cost optimization ignores that their primary value is licensing and isolation, not reducing spend for a standard stateless web workload.
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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.