Rsync is a tool in Linux to allow backups, you can backup a local folder to the local machine, or remote folders to remote machines (in any combination)
For my requirements, I want to backup a folder on my WebServer Pi, to a folder on my Backup Pi. Because the WebServer Pi faces the internet, I decided to use the Backup Pi to pull the files from the WebServer Pi, as the Backup Pi is not visible from the internet (so hopefully the whole process is a little more secure).
So lets say the WebServer Pi is 10.0.0.1 and the Backup Pi is 10.0.0.10. Lets also assume both Pi's have the default username and password of pi/raspberry.
Firstly, on the Backup Pi (10.0.0.10) I need to create a folder on my backup location, for this example we will use /backup/webserver
On the WebServer Pi, the files are held in /home/Pi
So from the Backup Pi, open a console and enter: rsync -avzh firstname.lastname@example.org:/home/pi /backup/webserver
If this is the first time the two computers have connected, then you may see a similar error to this one:
ECDSA key fingerprint is xx:xx:xx:xx:xx:xx:xx:xx:xx:xx:x:xx:xx:xx:xx:xx. Are you sure you want to continue connecting (yes/no)? Enter Yes to continue You will then be asked for your password (of the computer you are currently on)
That's it, you should be syncing.