[nylug-talk] [ot] managed DNS w/ monitoring?

[Chris Knadle]

On Tuesday 24 July 2007, jh wrote:
> I'm looking for a service that is a cross between SLA monitoring and
> Dynamic DNS - in other words, if a service is down, make change the DNS
> records to reflect.

   Although this does explain what you want, a specific example of what you're 
looking to do would be helful to illustrate.  For instance, you might have a 
set of round-robin-DNS entries in which you want to update or remove one of 
them if the service is down.

> Strangely, DynDNS has a monitoring service, and they obviously have the
> Dynamic DNS stuff, but they are not integrated at all (from what I could
> see).
>
> Anyone know of such a solution?

   Sadly I don't know of a Free OSS Dynamic DNS software package that would 
fit your needs yet.  The two Dynamic DNS software packages that I can find 
within the Debian tree are GnuDIP and DHIS-server.  GnuDIP is meant to be 
administered through a web page and stores data in a database, making that 
awkward to try to run scripts with.  DHIS-server uses UDP packets on an 
unprivilaged port which routers seem to block, and also requires opening a 
port for the DHIS-server because while the initial connection is from 
client->server, all periodic updates after initiation are server->client.  In 
short, neither one of these seems to fit this need.

   Assuming you're running Bind9 the best I can suggest is to roll your own 
solution, perhaps using Nagios or 'mon' for the service monitoring portion, 
and using 'nsupdate' directly to do Dynamic DNS updates.  [nsupdate on Debian 
is in the dnsutils package rather than in the bind9 package.]




   Beyond implementation, you should also consider the implications related to 
TTL of dynamic entries.  The typical TTL for dynamic DNS entries I've seen is 
around 60 seconds.  That type of TTL is required in order to have cached DNS 
entries flushed and clients recheck often, but it also increases DNS request 
load from queries and backup DNS server sync.

   Assuming you're not the only admin on-site, you'll also want to document 
the use of dynamic DNS carefully.  You don't want one of your associates 
implementing dynamic DNS entries for every MX record in your domain, 
otherwise your story might|will|should eventually show up on the Daily WTF.

   -- Chris

-- 

Chris Knadle
Chris.Knadle at coredump.us