Please read more detailed info here.

Create configuration file: /root/dns_sync_slave2.conf

USERNAME="slave"
SERVER="121.122.123.124"
SSHPORT="22"
SOURCESYNCLOCATION="/var/named/slave"
CHECKMAINDNS="centos-webpanel.com"
LOCALSYNCLOCATION="/var/named/slave"
LOCALCONFFILE="/etc/named/slave_additional.conf"

* SERVER = IP of Slave DNS Server & Manager.
* SSHPORT = SSH-Port of Slave DNS Server & Manager.
* SOURCESYNCLOCATION = Location of DNS zone files on Slave DNS Server & Manager.
* CHECKMAINDNS = This is a domain used for testing Slave DNS Server & Manager, it can be any and it doesn't need to be on the server.
* LOCALSYNCLOCATION = Location for DNS zone files on this local server.
* LOCALCONFFILE = Configuration files which contains the list of all zone files on this local server.

Setup cron how often you want to check for changes

crontab -e

* On servers with many clients and domains 100+ we recommend 5min cron.
* For servers with 1000+ you can go even with every 1-2 minutes.
example every 1 minute

* * * * * sh /scripts/dns_sync_slave2

In file /etc/named.conf after last include add:

include "/etc/named/slave_additional.conf";

Prepare config files

touch /etc/named/slave_additional.conf
chown named.named /etc/named/slave_additional.conf

go in cwp.admin -> Server Settings -> SSH Key Generator
there you need to generate new Keys

Go to Slave DNS Server & Manager
add key to the Slave DNS Server & Manager user you are using as "slave"

mkdir /home/slave/.ssh
nano /home/slave/.ssh/authorized_keys

** paste your key here which you had generated on the Slave2 DNS Server

chown -R slave.slave /home/slave/.ssh
chmod 600 /home/slave/.ssh/authorized_keys
chmod 700 /home/slave/.ssh/

You will also need to enable bash shell for that user so rsync could work

chsh -s /bin/bash slave

You can now test ssh connection like this from Slave2 DNS Server to Slave DNS Server & Manager
ssh slave@SERVER-IP -p SSH-PORT
If your connection goes ok without asking for the password then you are fully set.