We add/remove about 150 nodes every day to/from our monitoring system automatically via APIs. That use case has always sucked for me with Nagios. How would you do that?
Are you making the Nagios host pull (via NRPE) or are you asking the individual hosts to push (via NSCA)? I am trying to solve a similar problem. Given a dynamic population of hosts, each of which has a variable life span, I think that asking individual hosts to query their own state and then push that to a "monitoring receiver" is the most scalable, sustainable approach. At least, that's the theory I'll be testing this week.
We're not actually using Nagios. We use sensu because it was designed with this sort of dynamic environment in mind. (I'm trying to stay away from the "C" word. :)
In my current job, it's done automatically with Puppet. My previous job was a lot smaller scale and hosts were manually added to a config file of hosts, but I had set up groups properly so they only needed a single hostgroup to inherit all their services, dependencies and contacts from there.
