Custom Object Variables

Introduction

Users often request that new variables be added to host, service, and contact definitions. These include variables for SNMP community, MAC address, AIM username, Skype number, and street address. The list is endless. The problem that I see with doing this is that it makes Centreon Engine less generic and more infrastructure-specific. Centreon Engine was intended to be flexible, which meant things needed to be designed in a generic manner. Host definitions in Centreon Engine, for example, have a generic “address” variable that can contain anything from an IP address to human-readable driving directions - whatever is appropriate for the user’s setup.

Still, there needs to be a method for admins to store information about their infrastructure components in their Centreon Engine configuration without imposing a set of specific variables on others. Centreon Engine attempts to solve this problem by allowing users to define custom variables in their object definitions. Custom variables allow users to define additional properties in their host, service, and contact definitions, and use their values in notifications, event handlers, and host and service checks.

Custom Variable Basics

There are a few important things that you should note about custom variables:

  • Custom variable names must begin with an underscore (_) to prevent name collision with standard variables
  • Custom variable names are converted to all uppercase before use
  • Custom variables are inherited from object templates like normal variables
  • Scripts can reference custom variable values with macros and environment variables

Examples

Here’s an example of how custom variables can be defined in different types of object definitions:

define host{
  host_name      linuxserver
  _mac_address 00:06:5B:A6:AD:AA ; <-- Custom MAC_ADDRESS variable
  _rack_number R32               ; <-- Custom RACK_NUMBER variable
  ...
}

define service{
  host_name       linuxserver
  description     Memory Usage
  _SNMP_community public   ; <-- Custom SNMP_COMMUNITY variable
  _TechContact    Jane Doe ; <-- Custom TECHCONTACT variable
  ....
}

define contact{
  contact_name  john
  _AIM_username john16 ; <-- Custom AIM_USERNAME variable
  _YahooID      john32 ; <-- Custom YAHOOID variable
  ...
}

Custom Variables As Macros

Custom variable values can be referenced in scripts and executables that Centreon Engine runs for checks, notifications, etc. by using macros or environment variables. Custom variable macros are trusted (because you define them) and therefore not cleaned/sanitized before they are made available to scripts.

In order to prevent name collision among custom variables from different object types, Centreon Engine prepends “_HOST”, “_SERVICE”, or “_CONTACT” to the beginning of custom host, service, or contact variables, respectively, in macro and environment variable names. The table below shows the corresponding macro and environment variable names for the custom variables that were defined in the example above.

Object Type Variable Name Macro Name Environment Variable
Host MAC_ADDRESS $_HOSTMAC_ADDRESS$ NAGIOS__HOSTMAC_ADDRESS
Host RACK_NUMBER $_HOSTRACK_NUMBER$ NAGIOS__HOSTRACK_NUMBER
Service SNMP_COMMUNITY $_SERVICESNMP_COMMUNITY$ NAGIOS__SERVICESNMP_COMMUNITY
Service TECHCONTACT $_SERVICETECHCONTACT$ NAGIOS__SERVICETECHCONTACT
Contact AIM_USERNAME $_CONTACTAIM_USERNAME$ NAGIOS__CONTACTAIM_USERNAME
Contact YAHOOID $_CONTACTYAHOOID$ NAGIOS__CONTACTYAHOOID

Custom Variables And Inheritance

Custom object variables are inherited just like standard host, service, or contact variables.

Custom Variables and Centreon Broker

The configuration we talk about here is for advanced configurations. It can lead to malfunctions.

We know sending all custom variables to Centreon Broker can be long during a poller restart. Therefore, it is possible to filter them. This feature must be used by advanced users because it can break Centreon functionalities.

To acquieve this, there is two configuration variables that are:

  • enable_macros_filter: Its values are 1 or 0 to enable or disable the filter. By default its value is 0, all the values are sent.
  • macros_filter: This variable is a string. It is taken in account only when enable_macros_filter is enabled. Its value is custom variables to send to broker separated by commas.

Examples

Here’s an example of those two configurations variables:

enable_macros_filter=1
macros_filter=my_customvariable,service1_severity

Here, when the poller is restarted, only my_customvariable and service1_severity will be sent to Centreon Broker to store them in the Centreon storage database.