DEA-C01 Data Operations and Support Practice Question
A data engineer maintains an Amazon Kinesis Data Streams pipeline that feeds an AWS Lambda consumer. During traffic spikes, the Lambda function is throttled and records are reprocessed, causing duplicate entries in the downstream Amazon S3 sink. The engineer needs to reduce duplicates with the LEAST code change. What should the engineer do?
⚠ Common exam trap
The trap here is treating throughput tuning such as concurrency or enhanced fan-out as a fix for duplicates, when duplicates are an at-least-once delivery property that only idempotency resolves.
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
✓
Make the Lambda function idempotent by using the Kinesis sequence number as a deduplication key before writing to S3.
Duplicate delivery in Kinesis-to-Lambda pipelines is expected because Lambda retries batches after throttling or errors, and Kinesis guarantees at-least-once delivery. Making the consumer idempotent by keying on the Kinesis sequence number ensures that reprocessed records are detected and not written twice, which requires only a small change inside the function.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Configure the event source mapping's StartingPosition to LATEST and enable enhanced fan-out on the stream.
Why it's wrong here
StartingPosition LATEST controls where a new consumer begins reading and enhanced fan-out gives dedicated throughput per consumer, but neither prevents duplicates caused by Lambda retries after throttling. These settings affect read position and throughput, not idempotency, so duplicate records would still be written to the S3 sink during reprocessing.
- ✗
Increase the Lambda function's reserved concurrency and set the event source mapping's MaximumRetryAttempts to a low value.
Why it's wrong here
Raising concurrency helps with throughput but does not prevent duplicate processing, because Kinesis event source mappings retry failed batches and reprocess records after errors. Lowering MaximumRetryAttempts reduces retries but does not deduplicate records that were already processed before a failure, so duplicates can still reach the S3 sink.
- ✗
Enable the 'ReportBatchItemFailures' feature on the event source mapping and return the failed sequence numbers so only failed records are retried.
Why it's wrong here
ReportBatchItemFailures lets a Lambda consumer signal which records in a batch failed, so only those are retried. This reduces duplicate processing for partial batch failures, but the scenario describes throttling that causes whole-batch reprocessing, and it does not provide idempotent deduplication at the sink, so it is not the least-change fix for duplicates.
- ✓
Make the Lambda function idempotent by using the Kinesis sequence number as a deduplication key before writing to S3.
Why this is correct
Kinesis records carry a unique sequence number per shard, so using it as an idempotency key lets the Lambda function skip records it has already processed. This directly addresses duplicate writes at the sink with minimal code change, and it remains effective regardless of retries or throttling because reprocessed records are recognized and discarded.
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 and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
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.