- A
Elasticity
Correct. Elasticity refers to the ability to automatically provision and de-provision resources in response to real-time demand. The described auto-scaling behavior that adds and removes EC2 instances during flash sales is the classic example of elasticity.
- B
Scalability
Why wrong: Incorrect. While scalability involves the ability to increase capacity to handle growth, it does not inherently require automatic scaling down. The scenario specifically requires automatic removal of resources when traffic decreases, which is a key aspect of elasticity rather than scalability alone.
- C
High availability
Why wrong: Incorrect. High availability focuses on ensuring that applications remain operational and accessible despite component failures (e.g., distributing across multiple Availability Zones). It does not directly address dynamic capacity adjustments based on load changes.
- D
Fault tolerance
Why wrong: Incorrect. Fault tolerance is the ability of a system to continue operating even when one or more of its components fail. The scenario does not describe failure recovery, but rather the scaling of resources to match fluctuating demand.
CLF-C02 Cloud Concepts Practice Question
This CLF-C02 practice question tests your understanding of cloud concepts. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company runs an e-commerce website on Amazon EC2 instances behind an Application Load Balancer. The marketing team plans to run flash sales several times a year, which cause unpredictable but massive traffic spikes. The operations team wants the infrastructure to automatically add new EC2 instances when traffic increases and remove them when traffic decreases, without any manual intervention. Which cloud computing concept does this requirement MOST directly represent?
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
Elasticity
The requirement to automatically add EC2 instances during traffic spikes and remove them when traffic decreases directly represents elasticity. Elasticity is the ability to dynamically scale resources up or down based on real-time demand, which is precisely what the operations team needs for unpredictable flash sales. AWS Auto Scaling groups, integrated with the Application Load Balancer, automatically launch or terminate EC2 instances based on CloudWatch alarms (e.g., CPU utilization or request count), matching capacity to load without manual intervention.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Elasticity
Why this is correct
Correct. Elasticity refers to the ability to automatically provision and de-provision resources in response to real-time demand. The described auto-scaling behavior that adds and removes EC2 instances during flash sales is the classic example of elasticity.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Scalability
Why it's wrong here
Incorrect. While scalability involves the ability to increase capacity to handle growth, it does not inherently require automatic scaling down. The scenario specifically requires automatic removal of resources when traffic decreases, which is a key aspect of elasticity rather than scalability alone.
- ✗
High availability
Why it's wrong here
Incorrect. High availability focuses on ensuring that applications remain operational and accessible despite component failures (e.g., distributing across multiple Availability Zones). It does not directly address dynamic capacity adjustments based on load changes.
- ✗
Fault tolerance
Why it's wrong here
Incorrect. Fault tolerance is the ability of a system to continue operating even when one or more of its components fail. The scenario does not describe failure recovery, but rather the scaling of resources to match fluctuating demand.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse scalability (the ability to grow) with elasticity (the ability to both grow and shrink automatically), but the question explicitly requires automatic addition and removal of instances, which is the defining characteristic of elasticity.
Trap categories for this question
Scenario analysis trap
Incorrect. While scalability involves the ability to increase capacity to handle growth, it does not inherently require automatic scaling down. The scenario specifically requires automatic removal of resources when traffic decreases, which is a key aspect of elasticity rather than scalability alone.
Detailed technical explanation
How to think about this question
Under the hood, AWS Auto Scaling uses a target tracking scaling policy that adjusts the desired capacity of an Auto Scaling group based on a predefined metric, such as ALBRequestCountPerTarget, which is an average number of requests per EC2 instance over a period. A subtle behavior is that scaling policies have cooldown periods (default 300 seconds) to prevent rapid fluctuations, and the Auto Scaling group must have a minimum and maximum size set to define the boundaries of elasticity. In a real-world flash sale, if the ALB's request count spikes from 100 to 10,000 requests per second, the Auto Scaling group can launch dozens of instances within minutes, but the initial launch delay (e.g., AMI caching, user data scripts) can cause a temporary performance hit if not pre-warmed.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this CLF-C02 question test?
Cloud Concepts — This question tests Cloud Concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Elasticity — The requirement to automatically add EC2 instances during traffic spikes and remove them when traffic decreases directly represents elasticity. Elasticity is the ability to dynamically scale resources up or down based on real-time demand, which is precisely what the operations team needs for unpredictable flash sales. AWS Auto Scaling groups, integrated with the Application Load Balancer, automatically launch or terminate EC2 instances based on CloudWatch alarms (e.g., CPU utilization or request count), matching capacity to load without manual intervention.
What should I do if I get this CLF-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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