I use Amazon EC2 for my mobile app. Depending on load of the application at a given time, I might spawn new instances and then take them down when load is lower to save costs.

How does one keep up with Nagios configurations for such a dynamic environment? When one deals with managed hardware, configuration files are predictable. In this case Nagios, Capistrano and a bunch of other configuration files would need to be added. Capistrano needs to know where to deploy a new build to for an app server. Nagios needs to know to remove an existing instance or add a new instance for monitoring. Nagios also needs to know if a node was intentionally taken down or if the host is down due to error.

How is this done with the wonderful world of VPS/dynamic instances?