DEA-C01 Data Operations and Support Practice Question
A company runs a time-series forecasting model that writes results to an S3 bucket every 5 minutes. A downstream ETL job reads this data, but sometimes fails because it encounters incomplete files (zero bytes). What is the MOST reliable way to ensure the ETL job only processes complete files?
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 S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix.
S3 Event Notifications can trigger a Lambda function upon object creation, which can check the file size (e.g., > zero bytes) and then copy the file to a 'ready' prefix, ensuring the ETL job only processes complete files. Option A is wrong because an S3 Lifecycle policy can delete small files but does not prevent the ETL from reading incomplete files. Option B is wrong because S3 Copy does not verify completeness. Option C is wrong because S3 Select still reads the file even if it is incomplete; it doesn't guarantee completeness.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Set an S3 Lifecycle policy to delete files smaller than 1 MB.
Why it's wrong here
Does not ensure completeness; some valid files may be small.
- ✗
Use S3 Copy to move files to a 'processed' folder after the ETL job reads them.
Why it's wrong here
Does not address incomplete files; the job may still read incomplete files.
- ✗
Configure S3 Select to query the files and only return rows if the file is complete.
Why it's wrong here
S3 Select cannot detect incomplete files; it will simply return partial data.
- ✓
Use S3 Event Notifications to trigger a Lambda function that checks file size and then moves the file to a 'ready' prefix.
Why this is correct
Lambda can verify completeness before moving, ensuring only complete files are processed.
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 |
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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.