Security :: Secure And Automated Backups - Add Public Key To Authorized_hosts File On Prod Server?

I'm trying to find a secure way to backup files on my Prod Server to Backup Server. It must be automated, so I will need to run a command with cron which will login to Prod Server from Backup Server and backup data. 1. Do you think it would be secure enough to do this by creating an passwordless RSA private key on Backup Server and adding it's public key to authorized_hosts file on Prod Server? I can't think of a way to Automate this without having to enter any passwords without passwordless RSA key. Is there another. more secure way? 2. Should I create a special user for backup, which will only have read access to all files in the directory that I am backing up? If so, How can I run a check that this new backup user indeed has read access to ALL files in the folder that I intent to back up? How can I ensure the backup process will not skip files due to some permission problem? 3. I'm thinking of using rsnapshot tool, which uses rsync.