MLS-C01 Data Engineering Practice Question
A company uses Amazon Kinesis Data Firehose to deliver data to an Amazon S3 bucket. The data is organized by year/month/day/hour. The team needs to ensure that all data is encrypted at rest in S3 using an AWS KMS customer managed key (CMK). Which configuration should the team implement?
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
✓
In the Firehose delivery stream configuration, enable S3 destination encryption and select the customer managed KMS key.
The correct approach. Kinesis Data Firehose can be configured to encrypt data at rest in S3 using AWS KMS. In the Firehose delivery stream configuration, under S3 destination settings, you can enable encryption and select a customer managed KMS key. This ensures all data written to S3 is encrypted with that key. Option A is incorrect because S3 default encryption applies to objects uploaded directly to S3, but Firehose writes objects using its own IAM role and can override default encryption; configuring encryption in Firehose is the recommended way. Option B is incorrect because using a Lambda function to encrypt after delivery adds unnecessary complexity and latency; Firehose can encrypt natively. Option D is incorrect because a bucket policy denying PutObject without the correct KMS key would work but is not the simplest or most straightforward configuration; Firehose can handle encryption directly.
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 the S3 bucket's default encryption to use the customer managed KMS key.
Why it's wrong here
This works, but Firehose may not use it if it sets its own encryption; best to configure in Firehose.
- ✗
Use an AWS Lambda function to encrypt the data after it is delivered to S3.
Why it's wrong here
This adds unnecessary complexity and latency.
- ✓
In the Firehose delivery stream configuration, enable S3 destination encryption and select the customer managed KMS key.
Why this is correct
Firehose supports SSE-KMS for the S3 destination directly.
- ✗
Add a bucket policy that denies PutObject unless the request includes the correct KMS key.
Why it's wrong here
A bucket policy can enforce encryption, but it is more complex and may break the pipeline.
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.