CLF-C02 Cloud Technology and Services Practice Question
A company runs an application with variable workloads. During business hours, they need 10 EC2 instances; overnight they only need 2. Which combination minimizes cost while meeting this requirement?
⚠ Common exam trap
Many exam-takers choose Spot Instances (Option D) for cost savings without recognizing their lack of reliability for a workload requiring consistent availability during business hours, or they may over-purchase Reserved Instances (Option B) assuming all capacity must be reserved, ignoring the variable nature of the workload.
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
✓
2 Reserved Instances + Auto Scaling with On-Demand for variable demand
It uses 2 Reserved Instances to cover the baseline workload (overnight) at a lower cost, and Auto Scaling with On-Demand Instances to dynamically add capacity during business hours. Reserved Instances provide a significant discount over On-Demand for steady-state usage, while On-Demand instances handle variable demand without upfront commitment, minimizing total cost.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
10 On-Demand Instances running 24/7
Why it's wrong here
Running 10 On-Demand Instances 24/7 means you're billed per second for every instance-hour, with no upfront commitment or volume discount. Even when the application only needs 2 instances overnight, all 10 remain active and fully billed, so you pay for 8 idle instances every night. This strategy ignores workload patterns entirely and results in the maximum possible compute spend, with no mechanism to scale down unused capacity.
- ✗
10 Reserved Instances
Why it's wrong here
Purchasing 10 Reserved Instances gives you a meaningful discount over On-Demand pricing, but it also locks you into paying for 10 instances for the entire 1- or 3-year commitment term. Because the workload only requires a 2-instance baseline overnight, 8 of those Reserved Instances would be unused and still billed for the full term, wasting money on idle capacity. Overcommitting to RIs is a common cost-optimization mistake when demand is highly variable.
- ✓
2 Reserved Instances + Auto Scaling with On-Demand for variable demand
Why this is correct
Reserved Instances cover the predictable 2-instance baseline at the lowest possible price, while an Auto Scaling group uses On-Demand instances to handle the daytime spike. The scaling policy increases capacity during business hours and terminates those extra instances overnight, so you never pay for resources you aren't using. The design keeps the critical baseline always available via RIs, and uses On-Demand flexibility to match variable load.
- ✗
10 Spot Instances with Auto Scaling
Why it's wrong here
Spot Instances offer large discounts but come with the risk of interruption: AWS can reclaim the capacity with only a 2-minute warning when EC2 needs the resources back. Relying on 10 Spot Instances as the entire platform means the business-critical application could lose all capacity without warning, causing downtime. Spot is suitable for fault-tolerant or interruptible workloads, not for guaranteed availability, so this option fails to meet the reliability requirement.
Go deeper
Related to this question
About these practice questions
One of 993 original CLF-C02 practice questions on Courseiva, each with a full explanation and wrong-answer analysis — not exam dumps or protected exam content. Learn why practice questions differ from exam dumps →
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CLF-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 CLF-C02 exam.