MLS-C01 Data Engineering Practice Question
A data engineer needs to automate the transformation of CSV files to Parquet format as soon as they are uploaded to an S3 bucket. The transformed files should be stored in another S3 bucket. Which solution is the most cost-effective and requires the least maintenance?
⚠ Common exam trap
The trap here is that candidates often over-engineer the solution by choosing AWS Glue or EMR for a simple file format conversion, failing to recognize that Lambda is the most cost-effective and low-maintenance option for lightweight, event-driven transformations.
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
✓
Configure an S3 event notification to invoke a Lambda function.
AWS Lambda, triggered by S3 event notifications, provides a serverless, event-driven architecture that automatically converts CSV to Parquet upon file upload. This approach is cost-effective because you pay only for compute time during execution, and it requires minimal maintenance as AWS manages the infrastructure, scaling, and fault tolerance.
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 an S3 event notification to invoke a Lambda function.
Why this is correct
Lambda is serverless, pay-per-execution, ideal for this use case.
- ✗
Configure an S3 event notification to invoke an AWS Glue job.
Why it's wrong here
Glue has a minimum billing and is less cost-effective for small transformations.
- ✗
Run an Amazon EMR cluster continuously to watch for new files.
Why it's wrong here
EMR is expensive and high maintenance.
- ✗
Set up an EC2 instance with a cron job to poll the S3 bucket.
Why it's wrong here
EC2 requires management and is not cost-effective.
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 |
Go deeper
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This MLS-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 MLS-C01 exam.