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.
A data engineer is troubleshooting an AWS Glue job that reads from an S3 bucket and writes to another S3 bucket. The job fails with an 'Access Denied' error when trying to write to the output bucket. The IAM policy attached to the Glue service role is shown. What is the MOST likely cause of the failure?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The output bucket is not listed in the Resource of the IAM policy
The IAM policy attached to the Glue service role explicitly lists the output bucket in the Resource field. If the output bucket is not listed, the Glue job will receive an 'Access Denied' error when attempting to write to it, because the policy does not grant the necessary s3:PutObject permission for that bucket. This is the most direct cause of the failure.
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.
✗
The user who runs the job does not have S3 permissions
Why it's wrong here
The job runs under the service role, not the user.
✗
The Glue job role does not have permissions to start a job run
Why it's wrong here
The policy allows glue:StartJobRun.
✓
The output bucket is not listed in the Resource of the IAM policy
Why this is correct
The policy only allows PutObject on example-bucket, not the output bucket.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The S3 bucket policy denies access to the Glue service
Why it's wrong here
There is no indication of bucket policy; the IAM policy is insufficient.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may overlook the Resource field and assume the error is due to missing actions or user permissions, rather than recognizing that the IAM policy must explicitly list the destination bucket ARN for the write operation to succeed.
Detailed technical explanation
How to think about this question
AWS Glue jobs assume the IAM role specified in the job configuration to make API calls to S3. The IAM policy must include the specific bucket ARN (arn:aws:s3:::output-bucket-name) and optionally the object ARN (arn:aws:s3:::output-bucket-name/*) in the Resource element. Without this, the s3:PutObject action is not authorized, even if the action is listed in the Effect and Action fields. In practice, this often happens when a policy is copied from a template but the bucket name is not updated.
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 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.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: The output bucket is not listed in the Resource of the IAM policy — The IAM policy attached to the Glue service role explicitly lists the output bucket in the Resource field. If the output bucket is not listed, the Glue job will receive an 'Access Denied' error when attempting to write to it, because the policy does not grant the necessary s3:PutObject permission for that bucket. This is the most direct cause of the failure.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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