Dyn's free dynamic DNS service will be ending on Wednesday, May 7th, 2014.
CloudFlare, however, has a little known feature that will allow you to update your DNS records via API or a command line script called ddclient. This will give you the same result, and it's also free.
Unfortunately, ddclient does not work with CloudFlare out of the box. There is a patch available and here is how to hack[1] it up on Mac OS X.
ddclient 3.8.3 officially supports cloudflare, no more patching needed (hooray!) The following documentation is for Homebrew (The repo is currently hosting 3.8.2)
Homebrew, basic command line skills, and a domain name that you own.
Sign up to CloudFlare and add your domain name. Follow the instructions, the default values it gives should be fine.
You'll be letting CloudFlare host your domain so you need to adjust the settings at your registrar.
If you'd like to use a subdomain, add an 'A' record for it. Any IP address will do for now.
Let's get to business...
$ brew install ddclient
$ sudo cpan install JSON::Any
$ curl -O http://blog.peter-r.co.uk/uploads/ddclient-3.8.0-cloudflare-22-6-2014.patch
$ patch /usr/local/opt/ddclient/sbin/ddclient < ddclient-3.8.0-cloudflare-22-6-2014.patch
if the cpan mirror is too slow, add other mirrors from http://www.cpan.org/SITES.html
$ cp /usr/local/opt/ddclient/share/doc/ddclient/sample-etc_ddclient.conf /usr/local/etc/ddclient/ddclient.conf
$ vim /usr/local/etc/ddclient/ddclient.conf
Add:
##
### CloudFlare (cloudflare.com)
###
ssl=yes
use=web, web=dyndns
protocol=cloudflare, \
server=www.cloudflare.com, \
zone=domain.com, \
login=you@email.com, \
password=api-key \
host.domain.com
Comment out:
#daemon=300
Your api-key comes from the account page
ssl=yes might already be in that file
use=web, web=dyndns will use dyndns to check IP (useful for NAT)
$ sudo cp -fv /usr/local/opt/ddclient/*.plist /Library/LaunchDaemons
$ sudo launchctl load /Library/LaunchDaemons/homebrew.mxcl.ddclient.plist
You're done. Log in to https://www.cloudflare.com and check that the IP listed for your domain matches http://checkip.dyndns.com
[1] Don't do this in front of your boss.