问询：AWS Kinesis Firehose与S3间流量是否留存于亚马逊内网

1. Basic Question: Is Firehose-to-S3 traffic always within Amazon's internal network? #

Absolutely. When Kinesis Firehose and your target S3 bucket are in the same AWS Region, all data transfer between them stays entirely within AWS's private backbone network. This traffic never traverses the public internet—AWS handles this internally to ensure low latency, high reliability, and security.

2. Scenario-Specific Questions #

Let’s break down your setup and cross-region case clearly:

• Private Subnet Lambda → VPC Endpoint → Firehose → Same-Region S3:
  Your Lambda’s connection to Firehose uses a VPC endpoint (keeping that traffic within your VPC and AWS’s private network), but the Firehose-to-S3 segment is still managed entirely by AWS’s internal infrastructure. Even here, the data never leaves AWS’s private backbone—your VPC setup doesn’t change how Firehose communicates with S3 in the same region.

• Firehose to S3 in a Different Region:
  If your S3 bucket is in another AWS Region, Firehose will route the data through AWS’s global private backbone network (not the public internet). AWS’s cross-region traffic is fully contained within their own network infrastructure, so you don’t have to worry about exposure to public internet risks or variable public network latency here either.

A quick key takeaway: The way your source (Lambda) connects to Firehose (via VPC endpoint) only affects that first leg of the journey. Firehose’s communication with S3 is always handled over AWS’s private networks, regardless of your VPC configuration, as long as you’re using AWS-native services.

内容的提问来源于stack exchange，提问作者Mikhail Surovikov