DEA-C01 Data Operations and Support Practice Question
A company runs a data pipeline that uses AWS Lambda to process files uploaded to an S3 bucket. Recently, some files have been processed multiple times. The Lambda function is triggered by S3 event notifications. What is the MOST likely cause of duplicate processing?
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
✓
S3 event notifications are delivered at least once.
S3 event notifications are delivered at least once, meaning they can be sent multiple times, causing the Lambda function to be invoked repeatedly for the same file. This is the most likely cause of duplicate processing. Option A is incorrect: while Lambda retries on error for asynchronous invocations, it retries the same failed invocation, not creating multiple invocations for a successful event. Option B is incorrect: lack of idempotency does not cause duplicates; it simply means the function might not handle duplicates properly, but the root cause is the duplicate trigger. Option C is incorrect: reserved concurrency limits the number of concurrent executions but does not generate duplicate invocations.
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 has a high error rate and retries.
Why it's wrong here
Retries for failures do not cause duplicates on successful processing.
- ✗
The Lambda function is not idempotent.
Why it's wrong here
That is a result, not the cause.
- ✗
The Lambda function has a reserved concurrency setting.
Why it's wrong here
Concurrency does not cause duplicate events.
- ✓
S3 event notifications are delivered at least once.
Why this is correct
S3 can send duplicate events.
Visual reference
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 |
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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.