The answer is that the S3 bucket has a bucket policy that denies access to the Glue job’s IAM role, which is the most likely cause of the failure. Even when the IAM role grants full S3 access and its trust policy correctly allows the Glue service to assume it, an explicit deny in the S3 bucket policy overrides any allow—this is a fundamental principle of AWS authorization logic. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of how resource-based policies (like bucket policies) interact with identity-based policies (like IAM roles), a common trap where candidates overlook that a bucket policy can block access despite correct IAM permissions. The key memory tip is “Deny always wins”: no matter how permissive the role, a bucket policy’s explicit deny will stop the Glue job cold.
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.
An AWS Glue job is failing with an error that it cannot access an S3 bucket. The IAM role attached to the Glue job is shown in the exhibit. 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 S3 bucket has a bucket policy that denies access to this role
Option C is correct because the trust policy allows only Glue service to assume the role, but if the S3 bucket has a bucket policy that denies access to the role, the Glue job will fail. Option A is wrong because the trust policy allows Glue. Option B is wrong because the role has S3 full access. Option D is wrong because the role explicitly allows S3 access.
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 S3 bucket has a bucket policy that denies access to this role
Why this is correct
A bucket policy can override the role's permissions.
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 role lacks S3 permissions
Why it's wrong here
The role has AmazonS3FullAccess attached.
✗
The role does not have permission to call S3 APIs
Why it's wrong here
AmazonS3FullAccess grants all S3 actions.
✗
The trust policy does not allow Glue to assume the role
Why it's wrong here
The trust policy explicitly allows glue.amazonaws.com.
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.
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 S3 bucket has a bucket policy that denies access to this role — Option C is correct because the trust policy allows only Glue service to assume the role, but if the S3 bucket has a bucket policy that denies access to the role, the Glue job will fail. Option A is wrong because the trust policy allows Glue. Option B is wrong because the role has S3 full access. Option D is wrong because the role explicitly allows S3 access.
What should I do if I get this MLS-C01 question wrong?
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.
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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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.
Question Discussion
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