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 A is correct because even if the IAM role has S3 permissions, an S3 bucket policy that explicitly denies access to that role will override any allow. AWS evaluates all policies (identity-based and resource-based) and a deny in any policy results in a final deny decision. The error indicates the Glue job cannot access the bucket, which is consistent with a bucket-level deny.
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
The trap here is that candidates assume the IAM role's permissions are the only factor, ignoring that S3 bucket policies can independently deny access, which overrides any allow in the role's policy.
Detailed technical explanation
How to think about this question
AWS IAM policy evaluation logic uses an explicit deny as an override: if any policy (identity-based, resource-based, or service control policy) includes a Deny statement, the request is denied regardless of Allow statements. Bucket policies are resource-based policies attached directly to S3 buckets, and they can specify principals (like IAM roles) to deny access. In practice, a common misconfiguration is adding a bucket policy that denies all principals except a specific service, inadvertently blocking the Glue role.
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 S3 bucket has a bucket policy that denies access to this role — Option A is correct because even if the IAM role has S3 permissions, an S3 bucket policy that explicitly denies access to that role will override any allow. AWS evaluates all policies (identity-based and resource-based) and a deny in any policy results in a final deny decision. The error indicates the Glue job cannot access the bucket, which is consistent with a bucket-level deny.
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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