Amazons CloudFront service can be utilized by following these steps:

Without custom domain:

1. Create a CloudFront distribution for your Amazon S3 Bucket.
2. In the Amazon S3 module settings, check the Enable CNAME box.
3. In the CDN Domain Name field enter your CloudFront distribution domain name (e.g. xxxxxxxx.cloudfront.net)
4. Save the configuration and then clear the Drupal cache.

To use a custom domain:

The AmazonS3 module allows the local file system to be replaced with S3. Uploads are saved into the drupal file table using D7's new file/stream wrapper system.

You can switch it on as the default file system scheme, or individually for file and image fields.

It includes support for Amazon Cloudfront as well, through the use of a CNAME.