The answer is that the IAM policy likely lacks the `s3:PutObject` permission on the bucket resource itself, not just on the object ARN. When configuring IAM policies for SSE-S3 in S3, AWS requires that write operations involving encryption headers—such as those used by a Glue ETL job with SSE-S3 (AES256)—be authorized at both the bucket and object levels. The `s3:PutObject` action on the bucket ARN (`arn:aws:s3:::bucket`) is necessary for bucket-level checks that occur before the object-level write, and omitting it causes an 'Access Denied' error even if the object-level permission is present. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this tests your understanding of S3 permission granularity and how encryption settings interact with IAM policies, a common trap where candidates assume object-level permissions suffice. Remember the mnemonic: "Bucket before object" — always grant `s3:PutObject` on the bucket ARN when encryption headers are involved.
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.
A data engineer created an IAM policy to allow a Glue ETL job to read and write objects to an S3 bucket. The ETL job fails when writing data with the error 'Access Denied'. The job is configured to use SSE-S3 (AES256) encryption. What is the likely issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The policy does not grant s3:PutObject on the bucket itself, which is needed for some write operations.
The error 'Access Denied' when writing to S3 with SSE-S3 encryption typically occurs because the IAM policy lacks the `s3:PutObject` permission on the bucket resource itself. While the policy may grant `s3:PutObject` on the object ARN (`arn:aws:s3:::bucket/*`), some S3 write operations—especially those involving encryption headers or bucket-level checks—also require the permission on the bucket ARN (`arn:aws:s3:::bucket`). Without this, the request is denied even if the object-level permission exists.
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 grants s3:PutObject on all buckets, not just the specific one.
Why it's wrong here
The resource is specific to the bucket.
✗
The condition requires objects to be encrypted with SSE-KMS, but the job uses SSE-S3.
Why it's wrong here
The condition specifies AES256, which is SSE-S3.
✓
The policy does not grant s3:PutObject on the bucket itself, which is needed for some write operations.
Why this is correct
Bucket-level permissions may be required for certain write operations.
Related concept
Read the scenario before looking for a memorised answer.
✗
The condition requires objects to use SSE-S3, but the job uses SSE-KMS.
Why it's wrong here
The job uses SSE-S3, not SSE-KMS.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume `s3:PutObject` on the object ARN is sufficient for all write operations, overlooking that S3 requires the same permission on the bucket ARN for certain encryption-related or bucket-policy-evaluation scenarios.
Detailed technical explanation
How to think about this question
S3 bucket policies and IAM policies differentiate between bucket-level and object-level actions. The `s3:PutObject` action on the bucket ARN (`arn:aws:s3:::bucket`) is required for operations that S3 treats as bucket-level, such as writing objects with specific encryption headers or when the bucket has a default encryption setting that must be evaluated. This is a common oversight because many developers assume object-level permissions alone suffice, but S3's authorization model checks both the bucket and object ARN depending on the request context.
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.
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 policy does not grant s3:PutObject on the bucket itself, which is needed for some write operations. — The error 'Access Denied' when writing to S3 with SSE-S3 encryption typically occurs because the IAM policy lacks the `s3:PutObject` permission on the bucket resource itself. While the policy may grant `s3:PutObject` on the object ARN (`arn:aws:s3:::bucket/*`), some S3 write operations—especially those involving encryption headers or bucket-level checks—also require the permission on the bucket ARN (`arn:aws:s3:::bucket`). Without this, the request is denied even if the object-level permission exists.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A data engineer is configuring an IAM policy to allow users to upload objects to an S3 bucket only if the objects are encrypted using SSE-S3. However, users are getting AccessDenied errors when uploading objects without specifying encryption. What is the most likely cause?
hard
A.The condition should check for aws:SourceIp instead of encryption
✓ B.The condition requires encryption to be specified, but the upload does not specify it
C.The policy is attached to the wrong IAM user
D.The bucket policy denies all PutObject without encryption
Why B: Option B is correct because the policy allows PutObject only when encryption is AES256, but denies when no encryption is specified because the condition is not met. Option A is wrong because it's not a service control policy; Option C is wrong because the bucket policy is not shown; Option D is wrong because the condition checks for AES256, not KMS.
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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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