Decreasing Firehose Delivery Latency with Buffer Interval Tuning
A company is ingesting log files from multiple EC2 instances into Amazon S3 using the CloudWatch agent. The logs are delivered to a CloudWatch Logs group, and a subscription filter sends them to a Lambda function for transformation, then to Firehose. The Firehose stream is configured with a buffer interval of 60 seconds and buffer size of 5 MB. The logs are critical and must be available in S3 within 5 minutes. What is the most cost-effective way to reduce the delivery latency?
⚠ Common exam trap
It's easy for candidates to think increasing buffer size or interval improves throughput, but the question asks for reduced latency, so decreasing the buffer interval is the direct and cost-effective solution.
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
✓
Decrease the buffer interval to 10 seconds
Decreasing the Firehose buffer interval to 10 seconds directly reduces the maximum time data waits in the buffer before being delivered to S3, ensuring logs reach S3 within the required 5-minute window. Since the current 60-second buffer interval is the primary contributor to latency, lowering it to 10 seconds minimizes delivery delay without incurring additional costs, as Firehose charges are based on data volume, not buffer frequency.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Replace Firehose with Amazon Kinesis Data Streams
Why it's wrong here
KDS adds cost and requires additional consumers.
- ✗
Increase the buffer size to 10 MB
Why it's wrong here
Larger buffer size increases latency.
- ✗
Increase the buffer interval to 120 seconds
Why it's wrong here
Increases latency.
- ✓
Decrease the buffer interval to 10 seconds
Why this is correct
Lower buffer interval reduces delivery latency.
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 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.