The answer is that the bucket policy on my-bucket explicitly denies access to the IAM role. This is correct because in AWS, an explicit deny in a resource-based policy, such as an S3 bucket policy, always overrides any allow granted by an identity-based policy like the IAM role policy attached to the SageMaker training job. Even when the IAM role policy correctly grants s3:GetObject access to the specific object, the bucket policy’s explicit deny takes precedence, causing the access denied error. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this scenario tests your understanding of policy evaluation logic, specifically the distinction between identity-based and resource-based policies and the precedence of explicit denies. A common trap is assuming that a correct IAM role policy alone guarantees access, but you must always check for conflicting bucket policies. Remember the memory tip: “An explicit deny is the final say.”
MLS-C01 Modeling Practice Question
This MLS-C01 practice question tests your understanding of modeling. 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 scientist is setting up an IAM role for an Amazon SageMaker training job. The policy shown is attached to the role. The training job fails with an access denied error when trying to read the training data from s3://my-bucket/training/data.csv. What is the most likely reason?
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.
The bucket policy on my-bucket denies access to the IAM role
The IAM policy allows GetObject, but the bucket policy may have a deny rule that overrides the allow.
B
The training job is using a different IAM role
Why wrong: The training job would use the specified role; if it used a different role, the error would still be access denied but the exhibit shows the role's policy.
C
The IAM policy is missing the s3:ListBucket permission
Why wrong: S3 GetObject does not require ListBucket; the error is about reading the object, not listing.
D
The IAM role does not have permission to access the bucket location
Why wrong: The policy explicitly allows GetObject on the training prefix, which includes data.csv.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The bucket policy on my-bucket denies access to the IAM role
Option A is correct because the IAM policy shown grants s3:GetObject access to the bucket and object, but the training job still fails with an access denied error. The most likely cause is that the bucket policy on my-bucket explicitly denies access to the IAM role, overriding the IAM policy's allow. In AWS, an explicit deny in a resource-based policy (bucket policy) takes precedence over any allow in an identity-based policy (IAM role policy), causing the access denied error despite the IAM policy appearing sufficient.
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 bucket policy on my-bucket denies access to the IAM role
Why this is correct
The IAM policy allows GetObject, but the bucket policy may have a deny rule that overrides the allow.
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 training job is using a different IAM role
Why it's wrong here
The training job would use the specified role; if it used a different role, the error would still be access denied but the exhibit shows the role's policy.
✗
The IAM policy is missing the s3:ListBucket permission
Why it's wrong here
S3 GetObject does not require ListBucket; the error is about reading the object, not listing.
✗
The IAM role does not have permission to access the bucket location
Why it's wrong here
The policy explicitly allows GetObject on the training prefix, which includes data.csv.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume the IAM policy alone determines access, overlooking that resource-based policies (like S3 bucket policies) can override IAM permissions with explicit denies, especially when the bucket policy is not shown in the question.
Trap categories for this question
Command / output trap
The training job would use the specified role; if it used a different role, the error would still be access denied but the exhibit shows the role's policy.
Detailed technical explanation
How to think about this question
In AWS IAM, when both an identity-based policy (attached to the IAM role) and a resource-based policy (bucket policy) exist, the effective permission is the intersection of allows minus any explicit denies. An explicit deny in the bucket policy overrides any allow in the IAM policy, even if the IAM policy is broad. This is a common scenario when bucket policies are used to enforce cross-account restrictions or data perimeter controls, and the training job's role is not explicitly allowed in the bucket policy's Principal element.
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.
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.
Modeling — This question tests Modeling — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The bucket policy on my-bucket denies access to the IAM role — Option A is correct because the IAM policy shown grants s3:GetObject access to the bucket and object, but the training job still fails with an access denied error. The most likely cause is that the bucket policy on my-bucket explicitly denies access to the IAM role, overriding the IAM policy's allow. In AWS, an explicit deny in a resource-based policy (bucket policy) takes precedence over any allow in an identity-based policy (IAM role policy), causing the access denied error despite the IAM policy appearing sufficient.
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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