As a cloud server customer you get access to rackspace’s free DNS service.
When I fist saw this product I had an instance light-bulb moment, I could stop paying for a dynamic DNS service and build my own private one. As a broadband (DHCP) user I have a very basic requirement of needing to regularly update an A record so that I can find my pc 
To bring my idea into fruition I began researching; I need a cli tool which I could run from cron on my linux box (to send the DNS update requests to rackspace). In my research I found rscurl, a cli tool to control cloud servers, as rackspace have a standard API for all their products I have been able to use rscurl to develop rsdns.
rsdns is a series of cli tools to adding/deleting/changing rackspace DNS records, as part of the tool development I have created a script called rsdns-dc.sh to run on my machine, below is a short how to:
How to get free dynamic dns from rackspace.
Pre-requisit: This is for linux/mac, if you want to do this on windows you’ll need bash, curl, awk, sed & dig installed – google is your friend.
The instructions below assume that you (a) have a domain and (b) have already changed your NS records to point to dns1.stabletransit.com & dns2.stabletransit.com.
Download the latest rsdns from gitgub and unpack somewhere, I like ~/bin/rsdns.
Go to your rackspace management portal and grap your username & API key (It’s under “Your Account” -> “API Access”)
Create a config file for rsdns (~/.rsdns_config) with your settings.
RSUSER=linickx RSAPIKEY=123456 RSPATH=~/bin/rsdns/
You need your domain created on rackspace, you can either use rackspaces GUI to do this (It’s under “Hosting” -> “Cloud Servers” -> “serverabc” -> “DNS” ) or you can use rsdns, like so.
[LINICKX@SERVER rsdns]$./rsdns-domain.sh -d www.linickx.com -e spam@linickx.com
Once you have a domain setup you need an A record, this step was a deliberate design to avoid any rouge cron jobs from creating a million records, the dynamic client will only update an existing record – not create a new one.
To create the a record you going to need an IP address, it can be something random like the below, or you can use http://icanhazip.com to get your actual current IP. Again to create a record, you can use the rackspace GUI (It’s under “Hosting” -> “Cloud Servers” -> “serverabc” -> “DNS” -> “yourdomain” > “Add”) or you can use rsdns….
[LINICKX@SERVER rsdns]$./rsdns-a.sh -n dynamichost.linickx.com -i 123.123.123.123 -t 3600
In the above the TTL is set to 1hr, this is so that DNS caches do not keep the record too long. That’s all the pre-work done, now lets get your dynamic host setup!
The script to update your a record is rsdns-dc.sh, and you run it like this…
[LINICKX@SERVER rsdns]$./rsdns-dc.sh -n dynamichost.linickx.com
Easy huh? The script uses icanhazip to get your current IP, it then update the A record with it.
I never switch off my router so I have create a created a cronjob to run that script every 2 hours, plus the 1hr TTL should mean that the record is roughly in sync with my IP without making unnecessary requests – You can run the script more often if you like, just stay under the limits –> according to the API guidelines you can make upto 25 changes per min / 2 per second.
I use redhat based linux systems, so I can simply drop the following file called rsdns-dc into /etc/cron.d/ with this…
* */2 * * * linickx /home/linickx/bin/rsdns/rsdns-dc.sh -n dynamichost.linickx.com &>/dev/null
Now we are actually done! Free private Dynamic DNS on your own zone, what more could you want?
Nice work Nick!
I was thinking about doing this same thing, except a little more legit-like. Daemonize the script, maybe redoing it in python (not that bash isn’t capable.. nice work!), maybe starting a project around it, etc.
Thoughts?
Tweeks
p.s. FYI.. I am a Rackspace employee.. but am coming at this from the same angle you are. Please contact me and let me know your thoughts.
Hi,
I will respond to you email.
For those with similar questions, I’m happy for people to take this work further to create more/better/cooler open-source projects, the code is hosted on github to make forking as easy as possible
Great script.
Just to point out a mistake on the line where you say the script to update your ip. You wrote rsdns-a.sh but it should have been rsdns-dc.sh.
An addition to this script that would be nice is that it sends out the update command only if the ip is actually new. So there’s no update on the dns server if the ip has not change since the last call of the cron job.
What do you think, is it hard to implement ?
Nick
Typo fixed, thanks
The script should only update if the DNS response is differed to icanhazip; recently I pushed an “Internet availability commit” which should mean that many DNS errors are ignored.
I have development cron job which is on noisy mode, i.e. it emails me the output when it makes a change… which currently doesn’t happen very often at all.
I hope that helps,
Kind Regards,
Nick
Thank you sharing your nicely written code. I appreciate it. Jerry
Hi!
Am using your script. And it works fine.
A quick question. The script cannot update top-level domain A record?
When I tried to do so. It says the domain is not found.
Hi, yeah you are probably right. rsdns-a needed an extra -d (domain) switch to work with top level records. File an issue on GitHub and I’ll take a look in the new yr.
Rgds,
Nick