CLF-C02 Cloud Technology and Services Practice Question
A media company processes user-uploaded images. When a user uploads a high-resolution image to an Amazon S3 bucket, the company must automatically generate three resized thumbnail versions (small, medium, large) within seconds. The company wants a solution that requires no infrastructure management and scales automatically to handle thousands of concurrent uploads. Which AWS service should the company use to execute the thumbnail generation code?
⚠ Common exam trap
Many candidates choose Amazon ECS with Fargate (Option C) thinking it is the only serverless container option, but they overlook that Lambda is purpose-built for short-lived, event-driven tasks like image processing and requires no cluster or task definition management, making it the simpler and more cost-effective choice for this use case.
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 executes code in response to S3 events (e.g., object creation) without provisioning or managing servers. It scales automatically to handle thousands of concurrent uploads, and the 15-minute execution timeout is sufficient for generating three thumbnail versions within seconds. This meets the requirement for no infrastructure management and automatic scaling.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Run the thumbnailing code on Amazon EC2 instances behind an Application Load Balancer
Why it's wrong here
While EC2 instances can execute code, this approach requires manual scaling configuration, ongoing instance management, and a load balancer. It does not automatically react to S3 uploads without additional integration (e.g., S3 event notifications to an Amazon SQS queue that an EC2 instance polls). This adds operational overhead and does not provide the desired serverless, event-driven capability.
When this WOULD be correct
A company needs to run a long-running image processing job (e.g., generating thumbnails for a large batch of existing images) that exceeds the 15-minute Lambda timeout, and is willing to manage scaling and infrastructure.
- ✓
AWS Lambda
Why this is correct
AWS Lambda is a serverless function-as-a-service (FaaS) platform that runs code in response to events and automatically manages the underlying compute resources. It can be directly triggered by S3 bucket notifications (e.g., s3:ObjectCreated events). Lambda scales instantly to handle the upload volume and requires no server provisioning, making it ideal for this workload.
- ✗
Amazon ECS with AWS Fargate launch type
Why it's wrong here
Amazon ECS with Fargate is a serverless container orchestrator, but it requires building container images, defining task definitions, and managing a cluster. For a simple image resizing task that is event-driven and short-lived, using containers introduces unnecessary complexity compared to Lambda. Lambda is more suited for this granular, event-triggered workload.
When this WOULD be correct
A company needs to run a long-running image processing job (e.g., batch processing of thousands of high-resolution videos) that exceeds Lambda's 15-minute timeout, and wants to avoid managing servers. ECS with Fargate would be correct.
- ✗
AWS Elastic Beanstalk
Why it's wrong here
AWS Elastic Beanstalk is a Platform as a Service (PaaS) that automates the deployment and scaling of web applications. It still provisions underlying EC2 instances and manages the environment. It is not natively event-driven by S3 object creation; it expects a web server to handle HTTP requests. Using it for automated thumbnail generation upon S3 uploads would require additional architectural components and is not as straightforward as a Lambda trigger.
When this WOULD be correct
A company needs to deploy a web application with a custom runtime environment, requires full control over the underlying EC2 instances, and wants automated capacity provisioning, load balancing, and health monitoring, but does not need sub-second scaling or event-driven execution.
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
AWS Lambda is a serverless function-as-a-service (FaaS) platform that runs code in response to events and automatically manages the underlying compute resources. It can be directly triggered by S3 bucket notifications (e.g., s3:ObjectCreated events). Lambda scales instantly to handle the upload volume and requires no server provisioning, making it ideal for this workload.
✗Run the thumbnailing code on Amazon EC2 instances behind an Application Load BalancerWrong answer — click to see why▾
Why this is wrong here
EC2 with ALB requires manual scaling and infrastructure management, contradicting the requirement for no infrastructure management and automatic scaling to handle thousands of concurrent uploads.
★ When this WOULD be the correct answer
A company needs to run a long-running image processing job (e.g., generating thumbnails for a large batch of existing images) that exceeds the 15-minute Lambda timeout, and is willing to manage scaling and infrastructure.
Why candidates choose this
Candidates may think EC2 provides more control and is suitable for compute-intensive tasks, overlooking the serverless and auto-scaling requirements of the question.
✗Amazon ECS with AWS Fargate launch typeWrong answer — click to see why▾
Why this is wrong here
Amazon ECS with Fargate requires container image management and has higher startup latency than Lambda, making it less suitable for generating thumbnails within seconds for thousands of concurrent uploads without infrastructure management.
★ When this WOULD be the correct answer
A company needs to run a long-running image processing job (e.g., batch processing of thousands of high-resolution videos) that exceeds Lambda's 15-minute timeout, and wants to avoid managing servers. ECS with Fargate would be correct.
Why candidates choose this
Candidates know Fargate is serverless and can run containers, but overlook that Lambda is simpler and faster for short-lived, event-driven tasks like thumbnail generation triggered by S3 uploads.
✗AWS Elastic BeanstalkWrong answer — click to see why▾
Why this is wrong here
AWS Elastic Beanstalk requires managing an environment and does not provide the sub-second, event-driven, fully serverless execution needed for generating thumbnails within seconds for thousands of concurrent uploads without infrastructure management.
★ When this WOULD be the correct answer
A company needs to deploy a web application with a custom runtime environment, requires full control over the underlying EC2 instances, and wants automated capacity provisioning, load balancing, and health monitoring, but does not need sub-second scaling or event-driven execution.
Why candidates choose this
Candidates may think Elastic Beanstalk is a fully managed service that can automatically run code in response to S3 events, but it is designed for web applications, not event-driven functions, and still requires managing an environment.
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?”
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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JA
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.