How does Amazon S3 Transfer Acceleration accelerate S3 file transfers?

Question

I'm not clear how Amazon S3 Transfer Acceleration accelerates S3 file transfers.

I've been using https://docs.aws.amazon.com/AmazonS3/latest/dev/transfer-acceleration.html to refer to.

Supposing there is fileA in us-east-1, a user A in the UK, and there's a link to that fileA S3 endpoint.

Here's my understanding of how it works:

Before enabling Amazon S3 Transfer Acceleration user A would click on that link to fileA and it might take 10 seconds.

After enabling Amazon S3 Transfer Acceleration user A would click on that link to fileA and it might take 7 seconds.

I'm not clear how Amazon would achieve that reduction in time. It still has to get from the bucket to the user and goes over the public internet.

Or does Amazon intercept the link, move the file to a local CDN server in the meantime, then return a 302 to the new file location?

Answer 1

Under Amazon S3 Transfer Acceleration, the user is directed to the closest AWS endpoint and the request travels across the AWS network, which would have less hops and less traffic than the normal Internet.

Content is not cached.

From Amazon S3 Transfer Acceleration - Amazon Simple Storage Service:

Amazon S3 Transfer Acceleration enables fast, easy, and secure transfers of files over long distances between your client and an S3 bucket. Transfer Acceleration takes advantage of Amazon CloudFront’s globally distributed edge locations. As the data arrives at an edge location, data is routed to Amazon S3 over an optimized network path.

Answer 2

According the the Amazon S3 FAQ, Amazon S3 Transfer Acceleration leverages Amazon CloudFront’s globally distributed AWS Edge Locations. As data arrives at an AWS Edge Location, data is routed to your Amazon S3 bucket over an optimized network path.

However, this will not always lead to an increase in transfer speed. Each time you use S3 Transfer Acceleration to upload an object, AWS will check whether S3 Transfer Acceleration is likely to be faster than a regular Amazon S3 transfer. If AWS determines that S3 Transfer Acceleration is not likely to be faster than a regular Amazon S3 transfer of the same object to the same destination AWS Region, they will not charge for the use of S3 Transfer Acceleration for that transfer, and may bypass the S3 Transfer Acceleration system for that upload.