SOA-C02 Cost and Performance Optimization Practice Question
A company runs a production web application on a single Amazon EC2 instance. The application experiences a predictable and steady workload 24/7. The SysOps administrator wants to minimize compute costs for this instance while ensuring it remains available during the expected workload. Which EC2 purchasing option should the administrator use?
⚠ Common exam trap
It's easy for candidates to choose Spot Instances for cost savings, overlooking the critical requirement of 'remaining available during the expected workload' — Spot Instances can be interrupted at any time, making them unsuitable for production workloads that need consistent 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 most cost-effective option for a predictable, steady-state workload running 24/7. By committing to a 1- or 3-year term, you receive a significant discount (up to 72%) compared to On-Demand pricing, while still ensuring the instance remains available for the expected workload. This matches the requirement to minimize compute costs without sacrificing availability.
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 let you pay by the hour or second with no upfront commitment or long-term contract, which is ideal for short-term, spiky, or unpredictable workloads. For a production web application that runs continuously, you are paying the full On-Demand rate for every hour, making it the least cost-effective choice. The administrator can lower costs by purchasing a Reserved Instance that matches the instance family, region, and OS to lock in a lower hourly rate.
- ✓
Reserved Instances
Why this is correct
Reserved Instances offer a significant hourly discount in exchange for a one- or three-year commitment, and a Standard RI is best suited for steady-state, predictable production workloads like this always-on web app. By paying all or part of the cost upfront, you can reduce the effective hourly price by up to 72% compared to On-Demand. Because the workload is constant, the utilization will easily justify the commitment, making this the optimal cost-optimization strategy.
- ✗
Spot Instances
Why it's wrong here
Spot Instances provide access to spare EC2 capacity at discounts of up to 90%, but AWS can reclaim that capacity with only a two-minute warning when it needs it back. That means your production web application could suddenly lose an instance, causing downtime and violating availability requirements. Even with a mixed strategy of Spot and On-Demand, a critical production app should not rely on Spot for its baseline capacity because interruptions are inherent to the Spot model.
- ✗
Dedicated Hosts
Why it's wrong here
Dedicated Hosts give you a physical server entirely for your use, which is necessary for scenarios like Bring-Your-Own-License (BYOL) or regulatory compliance, but you pay for the entire host regardless of how many instances you run. For a single production web application, you'll likely be paying for far more capacity than you use, and the cost is typically higher than equivalent Reserved Instances. Additionally, Dedicated Hosts have a per-host billing model that does not align with cost optimization for a normal, non-license-bound workload.
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Same concept, more angles
1 more way 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 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?
easy- A.On-Demand Instances
- ✓ B.Reserved Instances (Standard, 1-year or 3-year)
- C.Spot Instances
- D.Dedicated Hosts
Why B: 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.
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.