I have read documents about them, but I don't know their difference exactly.
could you let me know what's the difference?
TL;DR: CloudFront is for content delivery. S3 Transfer Acceleration is for faster transfers and higher throughput to S3 buckets (mainly uploads).
Amazon S3 Transfer Acceleration is an S3 feature that accelerates uploads to S3 buckets using AWS Edge locations - the same Edge locations as in AWS CloudFront service.
However, (a) creating a CloudFront distribution with an origin pointing to your S3 bucket and (b) enabling S3 Transfer acceleration for your bucket - are two different things serving two different purposes.
When you create a CloudFront distribution with an origin pointing to your S3 bucket, you enable caching on Edge locations. Consequent requests to the same objects will be served from the Edge cache which is faster for the end user and also reduces the load on your origin. CloudFront is primarily used as a content delivery service.
When you enable S3 Transfer Acceleration for your S3 bucket and use <bucket>.s3-accelerate.amazonaws.com instead of the default S3 endpoint, the transfers are performed via the same Edge locations, but the network path is optimized for long-distance large-object uploads. Extra resources and optimizations are used to achieve higher throughput. No caching on Edge locations.
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