In case of passive checks as for example SNMP traps or notifications via email from external checking systems, it is not always possible to know if these controls are correctly performed.
This is the reason that made us decide to look for a solution able to ensure that the passive checks are being regularly provided by external applications. To reach our target we opted for the freshness check of Nagios, that as the word itself is suggesting is a check that verifies the freshness of the results provided.
Nagios, in fact, supports freshness checks on host and service passive check results. The freshness check aims to ensure that host and service checks are being passively provided by external applications on a regular basis. In particular, it will be guaranteed that the passive checks are registered in the expected time period. For example, if you have a daily check at 8 a.m., the freshness check will verify that the results are received exactly in that configured time frame.
How does it work?
Nagios performs periodic checks to verify the passive check results for all those hosts and services that have the freshness check enabled.
- A “freshness” threshold is calculated for each host or service
- For each host/service, the age of its last check result is compared with the freshness threshold.
- If last check result is received on a time above the freshness threshold, the check result is considered “stale”.
How is the Freshness Check enabled?
Here the procedure to follow to enable the freshness check:
- Use the check_service_freshness and check_host_freshness directives, that are already enabled by default in NetEye
- Use service_freshness_check_interval and host_freshness_check_interval options to tell Nagios how often it should check the freshness of service and host results – configuration already enabled by default in NetEye
- Enable freshness checking on a host- and service-specific basis by setting the check_freshness option and activating the checkbox near the same option in Monarch
- Configure freshness thresholds by setting the freshness_threshold option in your host and service definitions
- Configure the check_command option in your host or service definitions to reflect a valid command that should be used to actively check the host or service when it is detected as “stale”
- The check_period option in your host and service definitions is used when Nagios determines when a host or service can be checked for freshness, so make sure it is set to a valid timeperiod
Juergen Vigna
Author
