Synology NAS devices offer a built-in service to backup all configuration, applications and shared folders to a remote rsync server. Below is a short howto describing the steps required to setup the remote rsync services on a CentOS 6 server.

Install rsync and xinetd.

yum install rsync xinetd

Create configuration file.

# /etc/rsyncd.conf
gid = nobody
uid = nobody
read only = no
use chroot = yes 
transfer logging = true
log format = %h %o %f %l %b
log file = /var/log/rsyncd.log
secrets file = /etc/rsyncd.secrets
hosts allow = 192.168.1.0/24

[synology]
comment = Backup of Synology
path = /data/synology
auth users = synology

Create password file.

# /etc/rsyncd.secrets 
synology:plaintextpassword

Restrict its file permissions.

chmod 600 /etc/rsyncd.secrets

Enable rsync service in xinetd by setting disabled = no in /etc/xinetd.d/rsync and restart xinetd.

Open rsync port in iptables and make the change permanent.

iptables -I INPUT -p tcp -m state --state NEW -m tcp --dport 873 -j ACCEPT
service iptables save

Finally, fix selinux config and context of the destination directory.

setsebool -P allow_rsync_anon_write=1
chcon -t public_content_rw_t /data/synology

The Synology NAS should be able to establish a connection to the remote rsync server and do backups.