DEA-C01 Kinesis Data Firehose Lambda Integration Practice Question
A company uses Amazon Kinesis Data Firehose to deliver log data to Amazon S3. The data is transformed by a Lambda function that adds a timestamp field. Recently, the Firehose delivery stream has been failing with 'Lambda invocation failed' errors. The Lambda function's CloudWatch Logs show that the function is timing out. What is the MOST likely cause?
⚠ Common exam trap
Candidates often confuse timeout issues with permission or memory problems. Here, the CloudWatch Logs explicitly show timeouts, pointing to batch size or timeout configuration as the root cause.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Firehose buffer size is too large, causing the Lambda function to receive too many records.
Kinesis Data Firehose sends batches of records to the Lambda function for transformation. If the buffer size (or batch size) is too large, the Lambda function receives too many records and exceeds its configured timeout, causing 'Lambda invocation failed' errors. The timeout errors in CloudWatch Logs confirm this. Option A is incorrect because the function is being invoked, so Lambda permissions are working. Option C is incorrect because a 1-minute timeout may be insufficient for large batches. Option D is incorrect because the logs indicate a timeout, not an out-of-memory error.
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 lacks permission to write to CloudWatch Logs.
Why it's wrong here
Incorrect. The Lambda function is being invoked (it times out), so CloudWatch Logs permissions are not causing the failure.
- ✓
The Firehose buffer size is too large, causing the Lambda function to receive too many records.
Why this is correct
Correct. A large Firehose buffer size causes Lambda to receive a large batch, leading to timeout if the function cannot process it within its configured timeout.
- ✗
The Lambda function timeout is set to 1 minute, which is adequate.
Why it's wrong here
Incorrect. A 1-minute timeout is typical but may be too short for large batches, so it could be the cause of timeout.
- ✗
The Lambda function is running out of memory.
Why it's wrong here
Incorrect. The error is a timeout, not an out-of-memory error. Memory exhaustion would produce different errors.
Quick reference
AWS S3 Storage Class Comparison
| Storage Class | Min Duration | Retrieval | Use Case |
|---|---|---|---|
| S3 Standard | None | Immediate | Frequently accessed data |
| S3 Standard-IA | 30 days | Immediate | Infrequent access, rapid retrieval |
| S3 One Zone-IA | 30 days | Immediate | Non-critical infrequent data |
| S3 Intelligent-Tiering | None | Immediate–hours | Unknown or changing access patterns |
| S3 Glacier Instant | 90 days | Milliseconds | Archive with instant retrieval |
| S3 Glacier Flexible | 90 days | Minutes–hours | Archive, flexible retrieval |
| S3 Glacier Deep Archive | 180 days | Hours | Long-term compliance archive |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DEA-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 DEA-C01 exam.