Requirements

Perl 5.004 or later (you need the IO::Socket::SSL perl library for ssl-support)
Installation

cp ddclient /usr/sbin/
mkdir /etc/ddclient
mkdir /var/cache/ddclient
cp sample-etc_ddclient.conf /etc/ddclient/ddclient.conf
vi /etc/ddclient/ddclient.conf

—and change hostnames, logins, and passwords appropriately

For CloudFlare, this should be:

##
## CloudFlare (cloudflare.com)
##
ssl=yes
protocol=cloudflare,
server=www.cloudflare.com,
[email protected]
password=my-cloudflare-api-key
my-awesome-site.com,

To run in debug mode:

ddclient -daemon=0 -debug -verbose -noquiet

https://www.cloudflare.com/resources-downloads