It all depends on how you set up your environments, how complex they are, and what you are trying to back up.
How often do your environments change?
You can use something like Docker to keep track of the changes to your environments. It basically gives you version control for environments.
Read about rsync - https://wiki.archlinux.org/index.php/Full_system_backup_with_rsync
You could use rsync if you manually keep track of all of your config files and handle the scheduling and syncing yourself.
As for the actual site:
What's changing on your sites?
For changes to the code of a site, you should be using version control so that every single change is backed up to a repository like Github.
Most of the time though, the only thing that is changing is data in a database. Your database can easily be managed by a third party like Amazon RDS who offers automated backups. If you want to manage your own database on your own server, then you can have a cron job to automatically perform a backup of your database at scheduled times. Then you can use rsync to sync that backup to a separate machine. (You want to spread your backups across a couple of machines in different locations)