The answer is to configure the Firehose delivery stream to invoke a Lambda function for data transformation. This is the most cost-effective approach because Kinesis Data Firehose natively supports invoking a Lambda function on each incoming record batch, allowing you to add timestamps and mask email addresses in near-real-time without provisioning any servers. The Lambda function runs only when data is actively flowing through the stream, so you pay only for the compute time used during transformation, making it ideal for continuous ingestion. On the AWS Certified Data Engineer Associate DEA-C01 exam, this scenario tests your understanding of serverless, event-driven transformation patterns versus batch-oriented alternatives like AWS Glue, which would introduce unnecessary latency and cost. A common trap is to overcomplicate the solution with S3 Event Notifications or Athena, but remember that Firehose’s built-in Lambda integration is designed precisely for lightweight, record-level transformations. Memory tip: “Firehose + Lambda = transform on the fly, no extra services to buy.”
DEA-C01 Data Ingestion and Transformation Practice Question
This DEA-C01 practice question tests your understanding of data ingestion and transformation. 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 social media company ingests user activity data from multiple sources using Amazon Kinesis Data Firehose. The data is delivered to Amazon S3 in near-real-time. The company wants to transform the data by adding a timestamp and masking email addresses before storing it in S3. The transformation should be applied to all records. What is the most cost-effective way to implement this transformation?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Configure the Firehose delivery stream to invoke a Lambda function for data transformation.
Option A is correct. Kinesis Data Firehose can invoke a Lambda function to transform data on the fly. This is cost-effective because it runs only when data is flowing. Option B is wrong because Glue jobs are batch-oriented and add latency. Option C is wrong because S3 Events with Lambda adds complexity and cost. Option D is wrong because Athena is for querying, not transforming.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
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 Amazon Athena to run a CTAS query that transforms the data and writes to a new location.
Why it's wrong here
Athena is for querying, not for real-time transformation in the ingestion pipeline.
✗
Use AWS Glue to schedule a batch job every 5 minutes to transform the data.
Why it's wrong here
Batch processing adds latency and is not cost-effective for near-real-time.
✗
Use Amazon S3 Events to trigger a Lambda function whenever a new object is created.
Why it's wrong here
This would process files after they are stored, not before, and incurs additional S3 costs.
✓
Configure the Firehose delivery stream to invoke a Lambda function for data transformation.
Why this is correct
Firehose supports built-in Lambda transformation for real-time processing.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Data Ingestion and Transformation — This question tests Data Ingestion and Transformation — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Configure the Firehose delivery stream to invoke a Lambda function for data transformation. — Option A is correct. Kinesis Data Firehose can invoke a Lambda function to transform data on the fly. This is cost-effective because it runs only when data is flowing. Option B is wrong because Glue jobs are batch-oriented and add latency. Option C is wrong because S3 Events with Lambda adds complexity and cost. Option D is wrong because Athena is for querying, not transforming.
What should I do if I get this DEA-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DEA-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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