Collecting VPC Flow Logs from Multiple Accounts into a Single S3 Bucket
A company has a multi-account AWS environment. The security team wants to centrally manage VPC flow logs for all accounts. They already have a centralized logging account. What is the MOST scalable solution?
⚠ Common exam trap
Many exam-takers think CloudWatch Logs can natively publish to a cross-account log group, but it cannot; S3 with bucket policies is the correct scalable approach for multi-account VPC Flow Logs.
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 a CloudFormation StackSet to deploy VPC Flow Logs to an S3 bucket in the central account using bucket policies.
Using a CloudFormation StackSet allows you to deploy VPC Flow Logs consistently across multiple accounts and regions, publishing them to a centralized S3 bucket in the logging account. Bucket policies grant cross-account write access, making this approach highly scalable without per-account agent management or CloudWatch Logs cross-account limitations.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Deploy a third-party log collector agent on each EC2 instance.
Why it's wrong here
Instance agents capture host-level traffic only, missing VPC-level metadata such as ENI, subnet and action fields, and require per-instance deployment across every account. Agents suit deep packet or OS-level inspection, not centrally managed flow-log aggregation.
- ✗
Configure AWS Transit Gateway to aggregate flow logs.
Why it's wrong here
Transit Gateway aggregates network traffic routing between VPCs and on-premises networks, not flow log records; it cannot deliver logs to a central account. It is tempting because it centralises connectivity across many accounts, which would be correct if the requirement were hub-and-spoke routing rather than log aggregation.
- ✓
Use a CloudFormation StackSet to deploy VPC Flow Logs to an S3 bucket in the central account using bucket policies.
Why this is correct
StackSets deploy the flow-log configuration across every account and region from one template, while the central bucket policy authorises each account's log-delivery principal. This satisfies the scalability constraint by avoiding per-account manual setup as the organisation grows.
- ✗
Enable VPC Flow Logs in each account and publish to a CloudWatch Logs group in the central account.
Why it's wrong here
Cross-account CloudWatch Logs subscription is complex and has limits.
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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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This SAP-C02 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 SAP-C02 exam.