The answer is the Lambda function is missing the `firehose:DescribeDeliveryStream` permission on the Firehose delivery stream. This is because before a Lambda function can write records to a Kinesis Data Firehose, it must first call `DescribeDeliveryStream` to retrieve the stream’s endpoint and configuration details; without this permission, the SDK call fails with an access denied error even if other permissions like `s3:PutObject` are present. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of the specific IAM actions required for cross-service interactions—a common trap is assuming that write permissions alone (like `PutRecord` or `PutObject`) are sufficient, when in fact the Lambda needs a read-level describe action to resolve the target resource. A helpful memory tip: “Describe before Deliver”—the Lambda must first describe the Firehose stream to know where to send the data.
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.
A data engineer is troubleshooting a Lambda function that reads from a Kinesis Data Stream, processes records, and writes to a Kinesis Data Firehose delivery stream. The Firehose delivery stream is configured to deliver data to an S3 bucket. The Lambda function is failing with an access denied error. The IAM policy attached to the Lambda execution role is shown in the exhibit. Which permission is missing?
Why wrong: The function is reading from Kinesis, not writing to it; PutRecord is not needed.
B
firehose:DescribeDeliveryStream on the Firehose delivery stream
The Lambda function needs to describe the Firehose delivery stream to obtain the endpoint before putting records; the policy only allows PutRecord and PutRecordBatch but not DescribeDeliveryStream.
C
logs:CreateLogGroup and logs:CreateLogStream on the CloudWatch log group
Why wrong: While Lambda typically needs these permissions for logging, the error is access denied for Firehose, not for CloudWatch.
D
s3:PutObjectAcl on the S3 bucket
Why wrong: The function does not set ACLs; it writes via Firehose which handles S3 writes.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
firehose:DescribeDeliveryStream on the Firehose delivery stream
Option B is correct because the Lambda function needs permission to describe the Firehose delivery stream to get the endpoint, and kinesis:DescribeStream is already allowed for the Kinesis stream, but firehose:DescribeDeliveryStream is missing for the Firehose resource. Option A is wrong because Kinesis actions are allowed. Option C is wrong because s3:PutObject is allowed. Option D is wrong because the function is not writing to CloudWatch Logs; the error is about access to Firehose.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
kinesis:PutRecord on the Kinesis stream
Why it's wrong here
The function is reading from Kinesis, not writing to it; PutRecord is not needed.
✓
firehose:DescribeDeliveryStream on the Firehose delivery stream
Why this is correct
The Lambda function needs to describe the Firehose delivery stream to obtain the endpoint before putting records; the policy only allows PutRecord and PutRecordBatch but not DescribeDeliveryStream.
Related concept
Standard ACLs match source addresses.
✗
logs:CreateLogGroup and logs:CreateLogStream on the CloudWatch log group
Why it's wrong here
While Lambda typically needs these permissions for logging, the error is access denied for Firehose, not for CloudWatch.
✗
s3:PutObjectAcl on the S3 bucket
Why it's wrong here
The function does not set ACLs; it writes via Firehose which handles S3 writes.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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.
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: firehose:DescribeDeliveryStream on the Firehose delivery stream — Option B is correct because the Lambda function needs permission to describe the Firehose delivery stream to get the endpoint, and kinesis:DescribeStream is already allowed for the Kinesis stream, but firehose:DescribeDeliveryStream is missing for the Firehose resource. Option A is wrong because Kinesis actions are allowed. Option C is wrong because s3:PutObject is allowed. Option D is wrong because the function is not writing to CloudWatch Logs; the error is about access to Firehose.
What should I do if I get this DEA-C01 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related DEA-C01 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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