The correct answer is to enable exactly-once delivery on Kinesis Data Firehose and use the Kinesis Producer Library (KPL) with exactly-once semantics. This combination ensures that records are written to S3 without duplicates because KPL assigns unique sequence numbers to each record, and Firehose’s exactly-once delivery mode commits those records only once during the S3 write operation, preventing retry-induced duplicates. On the AWS Certified Machine Learning Specialty MLS-C01 exam, this question tests your understanding of streaming data durability within a Kinesis-to-S3 pipeline, often appearing as a trap where candidates mistakenly choose Lambda or SQS—neither of which natively guarantees exactly-once processing without custom idempotency logic. A key memory tip: think of KPL as the “producer guard” that stamps uniqueness, and Firehose as the “sink guard” that commits only once; together they form a two-layer exactly-once chain for Kinesis to S3.
MLS-C01 Data Engineering Practice Question
This MLS-C01 practice question tests your understanding of data engineering. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 designing a data pipeline that uses Amazon Kinesis Data Streams to ingest real-time transaction data. The data must be processed in near real-time and stored in Amazon S3 for long-term analytics. The engineer wants to ensure data durability and exactly-once processing semantics. Which TWO actions should the engineer take? (Choose two.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use the Kinesis Producer Library (KPL) with exactly-once delivery.
Correct options: C and D. Using the Kinesis Producer Library (KPL) with exactly-once delivery ensures no duplicates. Enabling Kinesis Data Firehose's exactly-once delivery to S3 ensures data is written exactly once. Option A (SQS) is not part of Kinesis. Option B (Glue) does not provide exactly-once for streaming. Option E (Lambda) can process records but does not guarantee exactly-once semantics without additional logic.
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.
✓
Use the Kinesis Producer Library (KPL) with exactly-once delivery.
Why this is correct
KPL provides exactly-once semantics when configured to do so.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use AWS Glue streaming ETL with checkpointing.
Why it's wrong here
Glue streaming ETL does not guarantee exactly-once semantics.
✓
Enable exactly-once delivery on Kinesis Data Firehose.
Why this is correct
Kinesis Data Firehose supports exactly-once delivery to destinations like S3.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use AWS Lambda with the Kinesis trigger and enable event source mapping with RetryAttempts set to 0.
Why it's wrong here
Lambda processes records at-least-once by default; setting RetryAttempts to 0 can cause data loss.
✗
Use Amazon SQS as the event source for downstream processing.
Why it's wrong here
SQS does not integrate directly with Kinesis Data Streams; it's a separate service.
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 MLS-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 Engineering — This question tests Data Engineering — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use the Kinesis Producer Library (KPL) with exactly-once delivery. — Correct options: C and D. Using the Kinesis Producer Library (KPL) with exactly-once delivery ensures no duplicates. Enabling Kinesis Data Firehose's exactly-once delivery to S3 ensures data is written exactly once. Option A (SQS) is not part of Kinesis. Option B (Glue) does not provide exactly-once for streaming. Option E (Lambda) can process records but does not guarantee exactly-once semantics without additional logic.
What should I do if I get this MLS-C01 question wrong?
Identify which MLS-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.
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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