The answer is that the Lambda function lacks the kms:Decrypt permission because the Kinesis stream is encrypted with a customer managed KMS key. Even though the IAM policy correctly grants kinesis:DescribeStream, GetShardIterator, and GetRecords, reading encrypted data from a Kinesis stream requires the Lambda execution role to have explicit permission to decrypt the stream’s data using the KMS key. Without kms:Decrypt, the GetRecords call succeeds in retrieving the encrypted records but then fails when the Lambda SDK attempts to decrypt them, producing 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 streaming services—a common trap is assuming that Kinesis-specific actions alone are sufficient. Remember the mnemonic: "Kinesis reads, KMS decrypts" to recall that encrypted streams always need a matching KMS permission.
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. 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.
Refer to the exhibit. An IAM policy for an AWS Lambda function. The Lambda function is triggered by an S3 event (object created) and needs to read from a Kinesis stream. However, the function fails with access denied when trying to read from Kinesis. 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 Kinesis stream is encrypted with a customer managed KMS key, and the Lambda function lacks kms:Decrypt permission
The Lambda function lacks permission to list the Kinesis stream (kinesis:ListStreams). The policy only allows DescribeStream, GetShardIterator, and GetRecords. To read from a stream, the initial DescribeStream call works, but the Lambda execution role may need additional actions depending on the SDK. However, often the error is due to missing kinesis:ListStreams if the SDK lists streams first. But more commonly, the policy is correct; the failure might be due to missing s3:ListBucket? No, the error is Kinesis. Actually, the policy allows GetRecords, so the most likely cause is that the Kinesis stream is encrypted with a KMS key and the Lambda function lacks kms:Decrypt permission. This is a common scenario. The policy does not include 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 Lambda function is not in the same region as the Kinesis stream
Why it's wrong here
Cross-region access is allowed if permissions are correct.
✗
The Lambda function does not have permission to list S3 buckets
Why it's wrong here
The error is about Kinesis, not S3.
✓
The Kinesis stream is encrypted with a customer managed KMS key, and the Lambda function lacks kms:Decrypt permission
Why this is correct
If the stream uses SSE-KMS, Lambda needs kms:Decrypt on the key.
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 S3 bucket policy denies access to the Lambda function
Why it's wrong here
The error is about Kinesis, not S3.
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 Ingestion and Transformation — This question tests Data Ingestion and Transformation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Kinesis stream is encrypted with a customer managed KMS key, and the Lambda function lacks kms:Decrypt permission — The Lambda function lacks permission to list the Kinesis stream (kinesis:ListStreams). The policy only allows DescribeStream, GetShardIterator, and GetRecords. To read from a stream, the initial DescribeStream call works, but the Lambda execution role may need additional actions depending on the SDK. However, often the error is due to missing kinesis:ListStreams if the SDK lists streams first. But more commonly, the policy is correct; the failure might be due to missing s3:ListBucket? No, the error is Kinesis. Actually, the policy allows GetRecords, so the most likely cause is that the Kinesis stream is encrypted with a KMS key and the Lambda function lacks kms:Decrypt permission. This is a common scenario. The policy does not include 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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