- A
Amazon EC2 Auto Scaling
Why wrong: Incorrect. Amazon EC2 with Auto Scaling still requires provisioning and managing Amazon Machine Images (AMIs), instances, and scaling policies. You pay for running instances even when no requests are being processed, which does not meet the 'pay only for compute time when requests are processed' requirement. It also involves more operational overhead than desired.
- B
AWS Lambda
Correct. AWS Lambda is a serverless compute service that runs your code only when triggered (e.g., via Amazon API Gateway). It automatically scales to handle any number of requests and you pay only for the compute time consumed during execution (per millisecond). There are no servers or containers to manage, aligning perfectly with the team's focus on writing code and minimizing operational overhead.
- C
AWS Fargate
Why wrong: Incorrect. AWS Fargate is a serverless compute engine for containers, but it still requires you to define and manage container images, task definitions, and service configurations. While it reduces server management, it is more complex than Lambda for simple API request processing. Additionally, you pay for the time your tasks are running, even if idle, which does not match the 'pay only for compute time when requests are processed' requirement as precisely as Lambda does.
- D
Amazon API Gateway
Why wrong: Incorrect. Amazon API Gateway is a fully managed service for creating, publishing, and managing REST APIs. However, it does not execute application code itself; it acts as a proxy or front door to a backend service (such as AWS Lambda or an HTTP endpoint). API Gateway must be used together with a compute service to process requests. Therefore, it alone does not meet the requirement for a compute service.
Quick Answer
AWS Lambda is the correct choice because it is the AWS serverless compute service for REST API backends with pay-per-request pricing, allowing developers to run code without provisioning or managing servers. When integrated with Amazon API Gateway, Lambda automatically scales from zero to handle unpredictable traffic spikes, executing code only when a REST API request is triggered by user actions in the mobile app, and billing solely for the compute time consumed during execution—no charges when idle. On the AWS Certified Cloud Practitioner CLF-C02 exam, this scenario tests your understanding of serverless architecture versus container-based services like Amazon ECS or EC2; a common trap is confusing Lambda with AWS Fargate, which still requires container management. Remember the key distinction: Lambda is event-driven, stateless, and abstracts all infrastructure. Memory tip: “Lambda Loves Low Loads”—it’s ideal when usage starts low, spikes unpredictably, and you want zero server management and pay-per-request pricing.
CLF-C02 Cloud Technology and Services Practice Question
This CLF-C02 practice question tests your understanding of cloud technology and services. 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 is developing a mobile application backend. The backend needs to process REST API requests that are triggered by user actions in the app. Usage is expected to start low but may spike unpredictably. The development team wants to focus solely on writing code and does not want to manage any servers or containers. The team also wants to only pay for compute time when requests are being processed. Which AWS service should the team use to meet these requirements?
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
AWS Lambda
AWS Lambda is the correct choice because it is a serverless compute service that runs code in response to REST API requests via Amazon API Gateway, automatically scaling from zero to thousands of concurrent executions. The team pays only for the compute time consumed while requests are being processed, with no charges when idle, and they never need to manage servers or containers.
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.
- ✗
Amazon EC2 Auto Scaling
Why it's wrong here
Incorrect. Amazon EC2 with Auto Scaling still requires provisioning and managing Amazon Machine Images (AMIs), instances, and scaling policies. You pay for running instances even when no requests are being processed, which does not meet the 'pay only for compute time when requests are processed' requirement. It also involves more operational overhead than desired.
- ✓
AWS Lambda
Why this is correct
Correct. AWS Lambda is a serverless compute service that runs your code only when triggered (e.g., via Amazon API Gateway). It automatically scales to handle any number of requests and you pay only for the compute time consumed during execution (per millisecond). There are no servers or containers to manage, aligning perfectly with the team's focus on writing code and minimizing operational overhead.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
AWS Fargate
Why it's wrong here
Incorrect. AWS Fargate is a serverless compute engine for containers, but it still requires you to define and manage container images, task definitions, and service configurations. While it reduces server management, it is more complex than Lambda for simple API request processing. Additionally, you pay for the time your tasks are running, even if idle, which does not match the 'pay only for compute time when requests are processed' requirement as precisely as Lambda does.
- ✗
Amazon API Gateway
Why it's wrong here
Incorrect. Amazon API Gateway is a fully managed service for creating, publishing, and managing REST APIs. However, it does not execute application code itself; it acts as a proxy or front door to a backend service (such as AWS Lambda or an HTTP endpoint). API Gateway must be used together with a compute service to process requests. Therefore, it alone does not meet the requirement for a compute service.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse AWS Fargate as a 'serverless' option, but Fargate still requires container management and incurs costs for provisioned vCPU and memory even when idle, whereas Lambda is truly serverless with no idle costs.
Detailed technical explanation
How to think about this question
AWS Lambda integrates natively with Amazon API Gateway to expose RESTful endpoints, and each Lambda function runs in a stateless, isolated environment with a maximum execution timeout of 15 minutes. Under the hood, Lambda uses a micro-VM (Firecracker) to provide strong isolation and rapid cold starts, and it scales horizontally by creating new function instances for each concurrent request. A real-world scenario is a mobile app backend that handles sporadic user actions like login or data fetch, where Lambda's pay-per-request model (priced per 1ms of execution and number of invocations) aligns perfectly with unpredictable traffic spikes.
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 Technology and Services — This question tests Cloud Technology and Services — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: AWS Lambda — AWS Lambda is the correct choice because it is a serverless compute service that runs code in response to REST API requests via Amazon API Gateway, automatically scaling from zero to thousands of concurrent executions. The team pays only for the compute time consumed while requests are being processed, with no charges when idle, and they never need to manage servers or containers.
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.
About these practice questions
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Last reviewed: Jun 11, 2026
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.
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