DBS-C01 Monitoring and Troubleshooting Practice Question
A company runs a document management system using Amazon S3 and Amazon DynamoDB. The application writes document metadata to DynamoDB and stores the document in S3. Recently, users report that occasionally documents are saved in S3 but the corresponding metadata is missing in DynamoDB. The application writes to DynamoDB first, then to S3. If the S3 upload fails, the application retries. The database specialist suspects a transaction consistency issue. The application is running on multiple EC2 instances behind an Application Load Balancer. What should the specialist recommend to ensure that both the metadata and document are stored consistently?
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 transactions to write metadata and initiate S3 upload within the same transaction.
Using DynamoDB transactions ensures atomicity; if the S3 upload fails, the transaction can be rolled back. Option B is wrong because DynamoDB Streams with Lambda introduces eventual consistency and possible duplicates. Option C is wrong because writing to S3 first still leaves inconsistency if DynamoDB fails. Option D is wrong because idempotency tokens help with duplicates but not atomicity.
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 DynamoDB transactions to write metadata and initiate S3 upload within the same transaction.
Why this is correct
Transactions provide atomicity across multiple items.
- ✗
Use DynamoDB Streams to trigger an AWS Lambda function that performs the S3 upload.
Why it's wrong here
This separates the operations; the DynamoDB write is committed before S3 upload.
- ✗
Reverse the order: upload to S3 first, then write to DynamoDB.
Why it's wrong here
If DynamoDB write fails, the document in S3 is orphaned.
- ✗
Implement an idempotency key in the application to retry the entire operation.
Why it's wrong here
Idempotency helps with retries but does not guarantee atomicity.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DBS-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 DBS-C01 exam.