Linux – How to setup a simple self-hosted dynamic DNS server

domain-name-systemdynamic-dnslinuxUbuntu

I have a small internal network of physical machines running hypervisors, which in turn run several KVM Ubuntu virtual machines. How would I setup an internal dynamic DNS server so that when I run a script to create a new virtual machine, that VM could automatically register itself in the DNS server?

Bind seems to be the standard DNS server for Linux, but it seems designed for a much more "static" DNS model. Dynamically updating this would require a complicated script that would have to SSH into the DNS server, edit configuration files, and then restart the server. This doesn't seem like a very elegant solution. Are there better options?

I saw a similar question, although they're asking for a solution for a public setting on Amazon. My servers are entirely private, and I don't want to rely on an external VM host or Dynamic DNS provider.

Best Answer

Actually Bind is capable of doing dynamic dns updates through RFC 2136 standard messages. Using the nsupdate tool and the right configuration (not terribly hard but not completely trivial either).

Your options for authenticating these update messages are 1) allowing only certain IPs to send update messages 2a) TSIG symmetrical encryption 2b) SIG(0) based public key cryptography or a combination of 1 and 2*. Among other places instructions can be found here

In implementing this personally I found the biggest problem was with giving named sufficient write privileges in /var/named. It needs to be able to create files in the directory as well as having write permissions to the files for the dynamic zones.

Sig(0) keys are generated with the dnssec-keygen utility with nametype HOST and keytype KEY. For exmaple (may not be exact)(RSAMD5 covers nearly every bind package):

dnssec-keygen -a RSAMD5 -b 1024 -n HOST -f Key host.domain.tld

The resulting .key file will be added to your zonefile, the .private will be specified on the commandline with nsupdate.

Related Solutions

GPO – Setting ‘Register This Connection’s Addresses in DNS’

There isn't a group policy setting to do what you're trying to do-- you're going to have to use a script.

First, I'd recommend reviewing the "Explain" tab for the settings you described above. You'll see that none of the settings actually turn on the registration behaviour you're looking for.

Assuming your machines get DNS settings from DHCP, and assuming that you don't mind this setting set back to the stock setting on all their network interfaces, assign the following in a Startup Script to the affected computers:

for /f "usebackq tokens=3* delims= " %%i in (`netsh interface ip show dns ^| find "Configuration for interface"`) do netsh interface ip set dns name=%%j source=dhcp primary

That will set the DNS client to get its address from DHCP, and reset the stock registration setting on all network interfaces on a Windows XP machine.

(An aside: You ought to figure out how your users changed that setting in the first place and stop them. It sounds like you have people who have 'Administrator' rights who shouldn't.)

Dynamic DNS for Shared Hosting – Does it exist

You've already mentioned DynDNS, it sounds like all you're missing is the client. They mention a couple linux-compatible clients on their website.

ddclient
inadyn

Using either of these in combination with a dynamic DNS service should accomplish what you want.

I originally assumed that your shared hosting would provide you with shell access. Without shell access, things get a bit tricky. First, you need some way to run a script periodically. Some web apps implement "fake cron" by calling a routine on every page load, but that won't help when your site isn't accessible. That means you need access to the crontab.

If you have the ability to run a task periodically, you could develop a script that sends the new IP address to another host you control, which is also the authoritative DNS. The receiving host would use the new IP address to update the zone file, then reload the DNS configuration.

TL;DR No, I don't know of any service that already provides this.

Best Answer

Related Solutions

GPO – Setting ‘Register This Connection’s Addresses in DNS’

Dynamic DNS for Shared Hosting – Does it exist

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