The Amazon S3 file transfer daemon is a daemon process that runs in the background and monitors folders. When it finds a file in one of the folders that matches a specific pattern it transfers that file to S3 storage and then removes the local copy. The folders monitored and the patterns searched for are controlled by a configuration file.
Included with the daemon is an apache module that handles requests for files in the folders monitored by the daemon. If a request comes in for a file and the file cannot be found locally the caller is sent a redirect to get the file directly from the S3 server. The redirect contains a signature created by the module using a public/private key combination that tells the S3 server that the caller is authorized to get the requested file. Included in the authorization is a time stamp that limits how long the URL/signature combination is good for.