- A
Enable DynamoDB auto scaling to increase write capacity and reduce throttling, which causes retries and duplicates.
Why wrong: Auto scaling does not prevent duplicates; it only reduces throttling.
- B
Use DynamoDB TransactWriteItems with a condition check that the record's Kinesis sequence number does not already exist in the table.
This ensures exactly-once semantics by atomically checking and writing.
- C
Place an Amazon SQS FIFO queue between the KCL application and DynamoDB to deduplicate messages.
Why wrong: This adds latency and does not guarantee exactly-once processing if the application fails after writing to SQS.
- D
Modify the application to use DynamoDB BatchWriteItem instead of PutItem to reduce the number of write requests.
Why wrong: BatchWriteItem does not provide deduplication; it can still write duplicate records.
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 company runs a real-time analytics platform that ingests IoT sensor data from millions of devices. The data is sent to Amazon Kinesis Data Streams with 16 shards. A custom Java application using the Kinesis Client Library (KCL) processes the data and writes aggregated results to Amazon DynamoDB. The application runs on a fleet of EC2 instances in an Auto Scaling group. Recently, the team noticed that some records are being processed multiple times, resulting in duplicate entries in DynamoDB. The application uses the DynamoDB PutItem API to write records. The team needs to eliminate duplicates without significantly increasing latency. Which solution should the team implement?
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
Use DynamoDB TransactWriteItems with a condition check that the record's Kinesis sequence number does not already exist in the table.
Option B is correct because using a DynamoDB transaction with a condition check on the Kinesis sequence number ensures that each record is written only once. Option A is wrong because idempotent writes would require a unique identifier; using PutItem with a condition expression on a unique attribute (like the sequence number) is effectively the same as option B but transactions provide atomicity. Option C is wrong because idempotent writes in DynamoDB are not natively supported; you must use conditional writes. Option D is wrong because adding a FIFO queue adds latency and complexity without guaranteeing exactly-once processing in the consumer.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Enable DynamoDB auto scaling to increase write capacity and reduce throttling, which causes retries and duplicates.
Why it's wrong here
Auto scaling does not prevent duplicates; it only reduces throttling.
- ✓
Use DynamoDB TransactWriteItems with a condition check that the record's Kinesis sequence number does not already exist in the table.
Why this is correct
This ensures exactly-once semantics by atomically checking and writing.
Related concept
Static NAT maps one inside address to one outside address.
- ✗
Place an Amazon SQS FIFO queue between the KCL application and DynamoDB to deduplicate messages.
Why it's wrong here
This adds latency and does not guarantee exactly-once processing if the application fails after writing to SQS.
- ✗
Modify the application to use DynamoDB BatchWriteItem instead of PutItem to reduce the number of write requests.
Why it's wrong here
BatchWriteItem does not provide deduplication; it can still write duplicate records.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
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FAQ
Questions learners often ask
What does this MLS-C01 question test?
Data Engineering — This question tests Data Engineering — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Use DynamoDB TransactWriteItems with a condition check that the record's Kinesis sequence number does not already exist in the table. — Option B is correct because using a DynamoDB transaction with a condition check on the Kinesis sequence number ensures that each record is written only once. Option A is wrong because idempotent writes would require a unique identifier; using PutItem with a condition expression on a unique attribute (like the sequence number) is effectively the same as option B but transactions provide atomicity. Option C is wrong because idempotent writes in DynamoDB are not natively supported; you must use conditional writes. Option D is wrong because adding a FIFO queue adds latency and complexity without guaranteeing exactly-once processing in the consumer.
What should I do if I get this MLS-C01 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related MLS-C01 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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Last reviewed: Jun 20, 2026
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