The documentation at https://www.cloudflare.com/technical-resources/#ddclient is incomplete as the ddclient Cloudflare protocol requires a ZONE to be defined as well, but even after looking at the source code here CloudFlare ddclient patch · GitHub and sample configuration shown below I am still non the wiser as to what I am supposed to put there.
Finally figured it out 
zone=domainname.tld and the host to update is the FQDN do that and everything works with ddclient.
However I also found another missing piece of information, you must pre-create a DNS record through the web interface before it can be updated using ddclient, else you get the error “No DNS record ID found.”