Why SageMaker Training Fails Due to S3 Bucket Policy Deny on ListBucket
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.
Refer to the exhibit. An ML engineer applies this bucket policy to an S3 bucket. The SageMaker execution role MySageMakerRole is used to train a model. The training data is located in s3://my-bucket/data/. The SageMaker training job fails with an access error. What is the most likely cause?
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 Deny statement on s3:ListBucket prevents the role from listing objects in the bucket.
Option C is correct because the Deny statement on s3:ListBucket explicitly denies the s3:ListBucket action for the MySageMakerRole. SageMaker training jobs require the ability to list objects in the bucket to discover and read training data, even if the GetObject permission is granted. The explicit Deny overrides any Allow, causing the access error.
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 policy allows GetObject only from the data/ prefix, but the training job uses a different prefix.
Why it's wrong here
The stem says data is in data/ prefix.
✗
The role is not in the same AWS account as the bucket.
Why it's wrong here
The role ARN uses account 123456789012, which is the same account.
✓
The Deny statement on s3:ListBucket prevents the role from listing objects in the bucket.
Why this is correct
SageMaker may need to list objects to iterate over files; the explicit deny blocks this.
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 bucket has default encryption enabled, causing a conflict.
Why it's wrong here
Default encryption does not cause access errors.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume GetObject alone is sufficient for reading data, but SageMaker training jobs also require ListBucket to enumerate objects in the prefix, and an explicit Deny on ListBucket overrides any Allow.
Detailed technical explanation
How to think about this question
SageMaker training jobs use the S3 API to list objects (ListObjectsV2) and then retrieve them (GetObject). Even if GetObject is allowed, the Deny on s3:ListBucket prevents the job from discovering which objects exist under the data/ prefix, causing a failure. This is a common misconfiguration where users grant read access but forget to allow listing, which is required for SageMaker's data channel setup.
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 Deny statement on s3:ListBucket prevents the role from listing objects in the bucket. — Option C is correct because the Deny statement on s3:ListBucket explicitly denies the s3:ListBucket action for the MySageMakerRole. SageMaker training jobs require the ability to list objects in the bucket to discover and read training data, even if the GetObject permission is granted. The explicit Deny overrides any Allow, causing the access error.
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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