Method:
Now let me explain you, how this method works in details. Let's say you are the person who registered domain example.com and hosted it to digitalocean.com. First of all you need to point your domain to digitalocean server, for that you need to create dns zone at digitalocean DNS server. DO itself give you name server addresses, which you need to bind to your domain. (example: ns1.digitalocean.com; ns1.digitalocean.com). After that you can successfully use your domain name to access your web service. Now you want to hide your server IP using cloudflare, and you are registering cloudflare account, following steps and cloudflare returns you new name server addresses (example: bart.ns.cloudflare.com; emma.ns.cloudflare.com).
Most of the people think that they successfully hide their sever IP address, but that's not true. Don't forget digitalocean still knows your domain real IP address, because you created the zone for it!!! And someone who is smart enough can use tool like nslookup and send requests to all public dns server and ask them to resolve your domain, when that person resolves example.com throw ns1.digitalocean.com as the response he will get real IP address of your domain. Below is the bash command which automates the process.


Code
$ for dnsServer in $(cat all.txt ); do if nslookup example.com $dnsServer |grep "Non-authoritative" -A2 | grep Address | awk {'print $2'} | grep -q "104.24";then echo $f;else echo "[+] Use Following Address: "$dnsServer;fi;done