These questions are independently created for study purposes. They are not official AWS exam questions, actual exam questions, leaked questions, or exam dumps.
CLF-005
Which of the following best describes scalability in the cloud?
Choices
Explanation and answer
Read the explanation and correct answer (spoiler — try answering first)
Correct answer: B. The ability to add or remove resources based on load.
Explanation
Scalability is the property of being able to increase or decrease system capacity in line with changes in load or number of users.
Per-choice explanations
A. A property that requires you to store data on paper.
Incorrect. This has nothing to do with storing on paper.
B. The ability to add or remove resources based on load.
Correct. Resources can be added or removed in line with load fluctuations.
C. A property that requires you to run only one server.
Incorrect. A single-server configuration tends to become a single point of failure and is not a description of scalability.
D. A property that requires you to manually approve all communications.
Incorrect. This is not a description of communication approval.
Practical Use
Scalability refers to the property of being able to add or remove processing capacity for a system in line with changes in load. There are two broad axes of expansion: vertical scaling (scaling up and scaling down), which increases the specifications of a single instance, and horizontal scaling (scaling out and scaling in), which adjusts the number of instances. AWS offers rich mechanisms to automate horizontal scaling. EC2 Auto Scaling Groups use CloudWatch metrics (such as CPU utilization or request count) as triggers to add and remove instances automatically. Because Lambda starts an execution environment per request, you barely need to be aware of scaling settings on the user side. A concept that is often confused with scalability is elasticity. Scalability refers to the static property of the ability to expand, while elasticity refers to the dynamic behavior of dynamically expanding and contracting in line with demand without holding on to wasted resources. The two concepts are close, but the exam can distinguish between them. In particular, the context of reducing resources when demand drops is more appropriately described as elasticity. Even when an application claims scalability, if the implementation holds state locally, it cannot scale horizontally. At design time, you need to consider making the application stateless and externalizing the session store. On CLF-C02, scalability is tested with a direct definition such as the property of being able to add or remove resources based on load. Distractors that have nothing to do with the concept, such as storing data on paper, manually approving communications, or running only one server, are common, and the correct answer can usually be narrowed down to one option. On the other hand, applied questions related to the performance efficiency pillar of the Well-Architected Framework ask in more depth about the distinction between scalability and elasticity, and the proper use of Auto Scaling and serverless.