- A
Amazon CloudWatch Events
Why wrong: CloudWatch Events can't directly trigger Rekognition; needs Lambda.
- B
Amazon Simple Notification Service (SNS)
Why wrong: SNS can notify but does not directly invoke Rekognition.
- C
AWS Lambda
Lambda can be triggered by S3 event and call Rekognition.
- D
AWS Step Functions
Why wrong: Step Functions can orchestrate but not directly triggered by S3 upload.
Question 1,226 of 1,755
MLS-C01 Practice Question: Machine Learning Implementation and Operations
This MLS-C01 practice question tests your understanding of machine learning implementation and operations. 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 using Amazon Rekognition to detect objects in images stored in S3. They want to reduce costs by processing images only when they are uploaded. Which AWS service should be used to trigger Rekognition automatically?
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 service because it can be triggered directly by S3 events (e.g., s3:ObjectCreated:Put) to invoke Amazon Rekognition's DetectLabels API on the newly uploaded image. This serverless architecture ensures processing occurs only on upload, eliminating idle costs and manual polling.
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 CloudWatch Events
Why it's wrong here
CloudWatch Events can't directly trigger Rekognition; needs Lambda.
- ✗
Amazon Simple Notification Service (SNS)
Why it's wrong here
SNS can notify but does not directly invoke Rekognition.
- ✓
AWS Lambda
Why this is correct
Lambda can be triggered by S3 event and call Rekognition.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
AWS Step Functions
Why it's wrong here
Step Functions can orchestrate but not directly triggered by S3 upload.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse S3 event notifications with CloudWatch Events or SNS, thinking those services can directly invoke Rekognition, but only Lambda (or an HTTP endpoint) can execute custom code to call the Rekognition API.
Detailed technical explanation
How to think about this question
Under the hood, S3 event notifications send a JSON payload to the configured Lambda function, which then uses the AWS SDK (e.g., boto3 for Python) to call Rekognition's detect_labels with the S3 object key and bucket. A subtle behavior is that S3 event notifications are asynchronous and may have a slight delay (typically within seconds), but they guarantee at-least-once delivery, so idempotent handling in Lambda is recommended to avoid duplicate processing.
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
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
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 |
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this MLS-C01 question test?
Machine Learning Implementation and Operations — This question tests Machine Learning Implementation and Operations — 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 service because it can be triggered directly by S3 events (e.g., s3:ObjectCreated:Put) to invoke Amazon Rekognition's DetectLabels API on the newly uploaded image. This serverless architecture ensures processing occurs only on upload, eliminating idle costs and manual polling.
What should I do if I get this MLS-C01 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
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
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Last reviewed: Jul 4, 2026
This MLS-C01 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 MLS-C01 exam.
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