The answer is that the Glue job’s IAM role lacks the kms:Decrypt permission for the KMS key used by the S3 bucket’s default encryption. When an S3 bucket has default SSE-KMS encryption enabled, any object written to it—including those delivered by Kinesis Data Firehose—is encrypted with that KMS key. Even though the Glue job’s role has s3:GetObject and s3:ListBucket permissions, reading the encrypted objects requires an additional kms:Decrypt action on the same key; without it, the S3 service returns an “Access Denied” error. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of how KMS encryption interacts with cross-service access, a common trap where candidates focus only on S3 permissions and forget the encryption layer. A key memory tip is “Get and List are not enough—you must Decrypt to read KMS-encrypted data.”
DEA-C01 Data Operations and Support Practice Question
This DEA-C01 practice question tests your understanding of data operations and support. 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 company uses Amazon Kinesis Data Firehose to deliver streaming data to an Amazon S3 bucket. The data is then processed by a scheduled AWS Glue ETL job that loads it into an Amazon Redshift table. Recently, the Glue job has been failing with the error: 'S3ServiceException: Access Denied'. The Firehose delivery stream is configured with a prefix and error logging to the same S3 bucket. The Glue job uses the same IAM role that has s3:GetObject and s3:ListBucket permissions on the bucket. 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 S3 bucket has default encryption enabled with AWS KMS (SSE-KMS), and the Glue job's IAM role lacks kms:Decrypt permission.
Option D is correct because Firehose uses SSE-S3 by default unless configured otherwise. If the S3 bucket has default encryption enabled with SSE-KMS, Firehose will use that encryption, but the Glue job's IAM role may lack kms:Decrypt permission for the KMS key. The error 'Access Denied' when reading from S3 often indicates encryption permission issues. Option A is wrong because the Glue job can read from S3 with the current permissions if no encryption is involved. Option B is wrong because the error is about access, not schema. Option C is wrong because the Glue job can use the same role as Firehose, but the role may not have KMS permissions.
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 Glue job expects a different data format than what Firehose writes.
Why it's wrong here
Format mismatch would cause a parsing error, not access denied.
✗
The Glue job's IAM role does not have s3:GetObjectVersion permission.
Why it's wrong here
Versioning is not mentioned; the error is not about version-specific access.
✗
The Glue job is using the wrong IAM role that does not have permissions to the S3 bucket.
Why it's wrong here
The role has s3:GetObject and s3:ListBucket, so access should be allowed if no encryption is involved.
✓
The S3 bucket has default encryption enabled with AWS KMS (SSE-KMS), and the Glue job's IAM role lacks kms:Decrypt permission.
Why this is correct
SSE-KMS requires kms:Decrypt permission; missing it causes access denied when reading.
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.
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 DEA-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 Operations and Support — This question tests Data Operations and Support — 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 default encryption enabled with AWS KMS (SSE-KMS), and the Glue job's IAM role lacks kms:Decrypt permission. — Option D is correct because Firehose uses SSE-S3 by default unless configured otherwise. If the S3 bucket has default encryption enabled with SSE-KMS, Firehose will use that encryption, but the Glue job's IAM role may lack kms:Decrypt permission for the KMS key. The error 'Access Denied' when reading from S3 often indicates encryption permission issues. Option A is wrong because the Glue job can read from S3 with the current permissions if no encryption is involved. Option B is wrong because the error is about access, not schema. Option C is wrong because the Glue job can use the same role as Firehose, but the role may not have KMS permissions.
What should I do if I get this DEA-C01 question wrong?
Identify which DEA-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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Question Discussion
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