DEA-C01 Data Ingestion and Transformation Practice Question
A company is using Amazon Kinesis Data Streams with a Lambda consumer to process real-time events. The Lambda function is triggered by a DynamoDB stream to update a counter. Recently, the counter has been inaccurate due to duplicate processing. What is the most likely cause?
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
✓
The Lambda function is not idempotent and is being retried on failures
The Lambda function is invoked at least once per record in the DynamoDB stream. If the function fails or times out, it may be retried, processing the same record again. If the function is not idempotent, this retry leads to duplicate updates to the counter. Option A is incorrect because TRIM_HORIZON is a Kinesis iterator type, not relevant to DynamoDB streams. Option B is incorrect because low reserved concurrency would cause throttling, not duplicate processing. Option D is incorrect because shard rebalancing occurs in Kinesis, not DynamoDB streams, and does not cause duplicates.
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 DynamoDB stream is configured with 'TRIM_HORIZON' iterator type
Why it's wrong here
Iterator type affects where to start reading, not duplication.
- ✗
The Lambda function's reserved concurrency is too low
Why it's wrong here
Low concurrency causes throttling, not duplicate processing.
- ✓
The Lambda function is not idempotent and is being retried on failures
Why this is correct
Retries cause duplicate updates if the function is not idempotent.
- ✗
The Kinesis stream has undergone a shard rebalance
Why it's wrong here
Rebalancing may cause reprocessing but not systematic duplicates.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
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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.