- 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.
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.
When this WOULD be correct
A company needs to run a stateful application that requires persistent storage or long-running processes, and expects steady or predictable traffic. The team is willing to manage server configurations but wants to automatically adjust capacity based on demand.
- ✓
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.
When this WOULD be correct
A team needs to run containerized applications without managing servers, but the workload has predictable or sustained usage patterns, and they are willing to pay for running containers even when idle. For example, a long-running microservice that processes messages from a queue.
- ✗
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.
When this WOULD be correct
A company wants to expose a RESTful API to external clients and needs features like request throttling, authentication, and API versioning. The team plans to integrate the API with a backend service (e.g., AWS Lambda or EC2) but wants to offload API management tasks. In this scenario, Amazon API Gateway would be the correct choice.
Option-by-option analysis
Why each answer is right or wrong
Understanding why wrong answers are wrong — and when they would be correct — is what separates a 750 score from a 900. The CLF-C02 exam frequently reuses these exact scenarios with slightly different constraints.
✓AWS LambdaCorrect answer▾
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.
✗Amazon EC2 Auto ScalingWrong answer — click to see why▾
Why this is wrong here
Amazon EC2 Auto Scaling still requires managing servers (EC2 instances) and incurs costs even when no requests are being processed, as instances must be running. The team wants to avoid server management and pay only for compute time during request processing.
★ When this WOULD be the correct answer
A company needs to run a stateful application that requires persistent storage or long-running processes, and expects steady or predictable traffic. The team is willing to manage server configurations but wants to automatically adjust capacity based on demand.
Why candidates choose this
Candidates may think Auto Scaling provides serverless-like scalability, but they overlook that it still involves managing EC2 instances and does not offer pay-per-request pricing.
✗AWS FargateWrong answer — click to see why▾
Why this is wrong here
AWS Fargate requires managing containers (even if serverless) and incurs costs for idle containers, whereas the team wants to only pay for compute time when requests are processed and avoid any container management.
★ When this WOULD be the correct answer
A team needs to run containerized applications without managing servers, but the workload has predictable or sustained usage patterns, and they are willing to pay for running containers even when idle. For example, a long-running microservice that processes messages from a queue.
Why candidates choose this
Candidates may confuse Fargate's 'serverless containers' with Lambda's 'serverless functions', not realizing Fargate still involves container orchestration and billing for provisioned resources, not per-request execution.
✗Amazon API GatewayWrong answer — click to see why▾
Why this is wrong here
Amazon API Gateway is a service for creating, publishing, and securing APIs, but it does not process the backend logic itself. It requires a compute service like AWS Lambda or EC2 to handle the actual request processing, so it alone does not meet the requirement to only pay for compute time when requests are processed.
★ When this WOULD be the correct answer
A company wants to expose a RESTful API to external clients and needs features like request throttling, authentication, and API versioning. The team plans to integrate the API with a backend service (e.g., AWS Lambda or EC2) but wants to offload API management tasks. In this scenario, Amazon API Gateway would be the correct choice.
Why candidates choose this
Candidates may confuse API Gateway with a compute service because it can trigger Lambda functions, but they overlook that API Gateway itself does not execute application code and is not a substitute for a compute service like Lambda.
Analysis generated from the official CLF-C02blueprint and verified against question context. The “when correct” sections are what AI assistants cite when candidates ask “what’s the difference between these options?”
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.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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.
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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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