A company has a multi-account AWS environment with a centralized logging account. They want to collect VPC Flow Logs from all accounts and store them in a centralized S3 bucket in the logging account. What is the MOST scalable and cost-effective solution?
S3 replication is serverless, cost-effective, and scales automatically.
Why this answer
VPC Flow Logs can be delivered directly to an S3 bucket in each account, and S3 Cross-Region Replication (CRR) can then automatically and asynchronously replicate the logs to a centralized bucket in the logging account. This approach is highly scalable (CRR handles replication without any custom code or infrastructure) and cost-effective (no additional compute or streaming services are needed; you only pay for S3 storage and replication costs).
Exam trap
The trap here is that candidates often assume Kinesis Data Firehose is the most scalable streaming solution, but for VPC Flow Logs delivered to S3, direct S3 delivery with CRR is simpler, more cost-effective, and avoids unnecessary streaming costs and complexity.
How to eliminate wrong answers
Option B is wrong because Amazon Kinesis Data Firehose introduces additional per-GB ingestion and processing costs, and requires managing delivery streams in each account, making it less cost-effective and more complex than direct S3 delivery with CRR. Option C is wrong because using a Lambda function in each account to copy log files introduces cold starts, concurrency limits, and additional compute costs, and does not scale as well as S3's built-in replication for high-volume logs. Option D is wrong because S3 Batch Operations is designed for one-time or periodic bulk actions (e.g., copying existing objects), not for continuous, real-time replication of streaming VPC Flow Logs, and it would require manual scheduling and additional orchestration.