When setting up alerts in Nagios some are better to be active while others can be passive. Further Active monitoring can be executed either on the Nagios server or started from Nagios but executed remotely, see diagram.
- Active Service Checks are initated by Nagios
- Ping or service check of exposed resources
- Remote Execution (nrpe) (ssh) for checking local resources like disk usage, processor load
- Passive Service Checks are initated by exteral commands