[mlieberman85]

If Nagios was a lightweight monitoring solution I would agree with you. Nagios however is a large monolithic system that is hard to integrate with third party metrics solutions, inventory management, etc. Though something like inventory management isn't part of monitoring it is still part of your whole system and if your monitoring solution can't easily integrate with your inventory management solution it gets frustrating.

I also tend to think service discovery or at least a flexible API that allows other systems to create new checks is a huge part of monitoring. Nagios' configuration files are a nightmare to deal with especially in a configuration managed environment.

[falcolas]

I think you're looking at it backwards. Nagios shouldn't integrate with your inventory management; inventory management should be configuring Nagios. Chef, Puppet and Ansible all have modules for idempotently configuring services in Nagios, making it simple to have your nagios configuration be part of your inventory management solution.

Ideally, this also resolves your configuration management problem as well. If it does not, there are tools which can probe a running Nagios state file, and provide you feedback on what's being monitored, and its state. The python library nagparser is one that I've used in the past to probe Nagios status for a status aggregation tool.