← MLS-C01·Amazon Web Services

Question 631 of 1,755

Data Engineering →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is to check the Lambda function’s resource-based policy to ensure S3 has permission to invoke the function. This is the correct diagnostic step because S3 event notifications require an explicit resource-based policy on the Lambda function that grants the S3 service principal the `lambda:InvokeFunction` action; without this permission, S3 cannot trigger the function at all, even if the event notification configuration is correctly set up on the bucket. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this question tests your understanding of cross-service permissions in event-driven ML pipelines, where a common trap is to confuse the Lambda execution role (needed for writing to the output bucket) with the resource-based policy (needed for S3 to invoke the function). A useful memory tip is “S3 needs an invite, not a role”—the bucket must be explicitly invited via the Lambda policy, while the execution role handles downstream actions.

MLS-C01 Data Engineering Practice Question

This MLS-C01 practice question tests your understanding of data engineering. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.

Exhibit

Refer to the exhibit.

```
{
  "Records": [
    {
      "eventVersion": "2.0",
      "eventSource": "aws:s3",
      "awsRegion": "us-east-1",
      "eventName": "ObjectCreated:Put",
      "s3": {
        "s3SchemaVersion": "1.0",
        "bucket": {
          "name": "my-input-bucket",
          "arn": "arn:aws:s3:::my-input-bucket"
        },
        "object": {
          "key": "data/file.csv",
          "size": 1024,
          "eTag": "abc123"
        }
      }
    }
  ]
}

A data engineer configures an S3 event notification to trigger an AWS Lambda function when a new object is created in 'my-input-bucket'. The Lambda function processes the CSV file and writes results to 'my-output-bucket'. The engineer notices that the Lambda function is not triggered for some objects. Which step should the engineer take to diagnose the issue?

Question 1hardmultiple choice

Full question →

Exhibit

Refer to the exhibit.

```
{
  "Records": [
    {
      "eventVersion": "2.0",
      "eventSource": "aws:s3",
      "awsRegion": "us-east-1",
      "eventName": "ObjectCreated:Put",
      "s3": {
        "s3SchemaVersion": "1.0",
        "bucket": {
          "name": "my-input-bucket",
          "arn": "arn:aws:s3:::my-input-bucket"
        },
        "object": {
          "key": "data/file.csv",
          "size": 1024,
          "eTag": "abc123"
        }
      }
    }
  ]
}

A
Check the Lambda function's execution role for permissions to write to the output bucket.
Why wrong: This would cause processing errors, not trigger failures.
B
Review the CloudWatch Logs for the Lambda function to see if there are errors.
Why wrong: If not triggered, there would be no logs.
C
Check the Lambda function's resource-based policy to ensure S3 has permission to invoke the function.
Missing invoke permission is a common cause of trigger failure.
D
Verify that the S3 event notification is configured with the correct prefix and suffix filters.
Why wrong: Filters could cause missing objects, but the engineer should check if notification is set up.

Full breakdown with real-world context →

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

✓

Check the Lambda function's resource-based policy to ensure S3 has permission to invoke the function.

Option D is correct. The most likely issue is missing permissions. The S3 bucket must have permission to invoke the Lambda function. The engineer should check the Lambda resource-based policy to ensure it allows invocation from S3. Option A is wrong because the event notification configuration is separate. Option B is wrong because the Lambda function's execution role needs permission to write to output bucket, but that would not prevent triggering. Option C is wrong because CloudWatch Logs would show invocations but not if not triggered.

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.

✗
Check the Lambda function's execution role for permissions to write to the output bucket.
Why it's wrong here
This would cause processing errors, not trigger failures.
✗
Review the CloudWatch Logs for the Lambda function to see if there are errors.
Why it's wrong here
If not triggered, there would be no logs.
✓
Check the Lambda function's resource-based policy to ensure S3 has permission to invoke the function.
Why this is correct
Missing invoke permission is a common cause of trigger failure.
Related concept
Read the scenario before looking for a memorised answer.
✗
Verify that the S3 event notification is configured with the correct prefix and suffix filters.
Why it's wrong here
Filters could cause missing objects, but the engineer should check if notification is set up.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.

Detailed technical explanation

How to think about this question

This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.

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.
Use explanations to understand the rule behind the answer.

TExam Day Tips

Underline the problem statement mentally.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.

What to study next

Got this wrong? Here's your next step.

Identify which MLS-C01 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.

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FAQ

Questions learners often ask

What does this MLS-C01 question test?

Data Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Check the Lambda function's resource-based policy to ensure S3 has permission to invoke the function. — Option D is correct. The most likely issue is missing permissions. The S3 bucket must have permission to invoke the Lambda function. The engineer should check the Lambda resource-based policy to ensure it allows invocation from S3. Option A is wrong because the event notification configuration is separate. Option B is wrong because the Lambda function's execution role needs permission to write to output bucket, but that would not prevent triggering. Option C is wrong because CloudWatch Logs would show invocations but not if not triggered.

What should I do if I get this MLS-C01 question wrong?

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 20, 2026

Question Discussion

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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.