Cloudflare + Dynamic DNS (ddclient) = Super Awesome

Instructions

# This guide will show you how to configure ddclient to dynamically update your DNS at Cloudflare.
# This cookbook makes use of a number of online guides - all of which I will reference at the end.

# Cloudflare requires ddclient to be version 3.8.2 or you will get a 'cloudflare protocol didn't exist'.
# Unfortunately, the package manager at this time makes use of 3.8.1
# My suggestion is to follow the semi-autonomous process, by downloading the out of date package
# and then manually update a few files. If you prefer, you can go down the fully manual route manual route. 
# Installation - Manual (Not Tested: https://www.cloudflare.com/technical-resources/#ddclient)

# Installation - Semi-Autonomous (Recommended, follow below)
sudo apt-get update
sudo apt-get install ddclient libjson-any-perl

# The version should be 3.8.1, which does not support Cloudflare. Check version number by running the command below. 
# Look for ...ddclient version 3.8.1
ddclient -h

# We manually upgrade the binary along with the configuration file. Check latest version: https://sourceforge.net/projects/ddclient/
# Download file:
wget http://downloads.sourceforge.net/project/ddclient/ddclient/ddclient-3.8.3.tar.bz2

# Extract
tar -jxvf ddclient-3.8.3.tar.bz2

# Copy the file from extracted directory and overwrite binary
sudo cp -f ddclient-3.8.3/ddclient /usr/sbin/ddclient

# From version 3.8.2 config file must be nested in a directory called ddclient, this is the final edit to our install: 
# Move ddclient.conf in a directory called ddclient: 
sudo mkdir /etc/ddclient
sudo mv /etc/ddclient.conf /etc/ddclient

# Awesome, we're almost there. Now just a little configuration. Navigate to directory and edit the config file: 
cd /etc/ddclient.conf
sudo nano ddclient.conf

# Copy the configuration like below. The config assumes you have the domain 'gudthing.co.uk'
# Replace text in login, password, zone, and domain
protocol=cloudflare
use=web
server=www.cloudflare.com
ssl=yes
[email protected]
password=YOUR-GLOBAL-API-KEY-https://www.cloudflare.com/a/account/my-account
zone=gudthing.co.uk
gudthing.co.uk

# Once done, press CTRL + O to write the changes, and hit ENTER to confirm your want to overwrite file and then exit CTRL + X
# Good news, you are technically good to go! Test your setup by: 
ddclient -daemon=0 -debug -verbose -noquiet

# Check the log and see if there are any messages. Most likely issues will be with config file, so update appropriately 
# Now our DNS details will get updated everytime we run the command above. Pretty cool, but we can do better. 
# Let's make it run every 5 minutes = 12 times an hour. We will do this via daemon, which will need another configuration file.
# Set the values to below:
sudo nano /etc/default/ddclient
run_ipup="false" 
run_daemon="true"
daemon_interval=5000

# Make sure you set run_ipup to false, of it will cause problems. 
# CTRL + O and then ENTER and lastly CTRL + X
# Configuration ready, now lets run the daemon:
sudo service ddclient start
sudo service ddclient status

# Optional - Create a cron job to force daily requirement 
# So far we have setup ddclient to run every 5 minutes. Every 5 mins it will check our WAN address and if it has changed
# it will talk to Cloudflare and update our DNS. The issue is that if our DNS doesn't change for a few days, then cloudflare
# will not hear from our server which may cause timeout issues/drops in connection or fail to update when duty calls. 
# With a cron job, we force a daily / weekly exchange: 
cd etc/cron.daily 

# create a file called ddclient with the following configuration
sudo nano /etc/cron.daily/ddclient
#!/bin/sh
/usr/sbin/ddclient -force

# Write, save and close file: CTRL + O, ENTER & CTRL + X
# The file we've just created is just a text file, lets make it executable: 
sudo chmod +x /etc/cron.daily/ddclient

# You're done! Now you can have all the benefits from Cloudflare + [free] DDNS!   
# API Key: https://www.cloudflare.com/a/account/my-account
# Binary: https://sourceforge.net/projects/ddclient/
# Resources: 
#     https://www.cloudflare.com/technical-resources/#ddclient
#     https://jenssegers.com/84/dynamic-dns-for-cloudflare-with-ddclient
#     https://samhobbs.co.uk/2015/01/dynamic-dns-ddclient-raspberry-pi-and-ubuntu

Is there a way to also update multiple subdomains?

Configure it to update only a single subdomain - say it's "ddns.domain.com". Then create CNAME records that point to "ddns".

Example:

• Cloudflare only updates ddns.domain.com
• You have CNAMEs called "foo" and "bar" that point to ddns.domain.com.
• Now if anyone goes to foo.domain.com or bar.domain.com, they'll go to the same IP associated with ddns.domain.com, which is dynamically updated via cloudflare-ddns.