CLF-C02 Cloud Concepts Practice Question
A company discovers they have 30 EC2 instances running 24/7 that are almost never used — CPU utilisation under 1%. Terminating these idle instances would save thousands of dollars per month. Which AWS Well-Architected Framework pillar encourages this practice?
⚠ Common exam trap
A common mix-up: candidates confuse 'Performance Efficiency' (which optimizes resource usage for performance) with 'Cost Optimization' (which minimizes waste and cost), leading them to select Option C instead of D.
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
✓
Cost Optimisation
The Cost Optimization pillar of the AWS Well-Architected Framework focuses on avoiding unnecessary costs by matching capacity with demand. Terminating idle EC2 instances (CPU utilization under 1%) directly reduces wasted spend, aligning with the pillar's principle of 'right-sizing' resources and eliminating unused components.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Operational Excellence
Why it's wrong here
Operational Excellence focuses on how teams manage, monitor, and improve operational processes, such as automation, logging, incident response, and continuous improvement of procedures. While terminating idle instances might be a result of an operational decision, the actual objective here is to eliminate wasted spend, which falls under financial management and cost optimization, not process efficiency. The activity does not improve deployment, reliability, or operational runbooks, so this pillar does not align with the question's intent.
- ✗
Reliability
Why it's wrong here
Reliability concerns a workload's ability to function correctly and recover from failures, including fault tolerance, backup, and resilient architecture. Terminating idle instances has no impact on system availability because those instances are not serving traffic or required for failover. If anything, removing unnecessary resources could slightly simplify the environment, but the motivation is purely to reduce cost, not to improve uptime or disaster recovery. Therefore, Reliability is not the correct pillar for this cost-saving action.
- ✗
Performance Efficiency
Why it's wrong here
Performance Efficiency is about matching infrastructure to workload demands, such as selecting appropriate instance families, storage tiers, or auto scaling policies to meet performance targets. While underutilization might be noticed during performance tuning, the core concern is whether resources satisfy throughput, latency, or concurrency requirements—not whether they are costing money with zero output. Terminating idle instances reduces waste and directly maps to cost controls, not performance tuning, so this pillar is not the best answer.
- ✓
Cost Optimisation
Why this is correct
The Cost Optimisation pillar explicitly includes the practice of 'eliminating unused and idle resources' as a foundational best practice. In this scenario, 30 idle EC2 instances are consuming compute capacity, storage, and possibly data transfer costs while delivering no business value. Terminating these instances reduces monthly expenditure without affecting any active workload, which is a textbook example of cost optimization. This is the correct pillar because the action is driven by financial waste, not technical capability.
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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.