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# Notes on low-level discovery

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#### Application discovery

Application prototypes support LLD macros.

One application prototype can be used by several item prototypes of the
same discovery rule.

If created application prototype is not used by any item prototype it
gets removed from 'Application prototypes' list automatically.

Like other discovered entities applications follow the lifetime defined
in discovery rule ('keep lost resources period' setting) - they are
removed after not being discovered for the specified number of days.

If an application is not discovered anymore, the application itself may
not be removed because of the 'lost resources period' setting, however:

-   items that are still discovered are automatically removed from it;
-   items that are no longer discovered are not removed from it (note
    that they would be removed before Zabbix 4.0.18).

Application prototypes defined by one discovery rule can't discover the
same application. In this situation only the first prototype discovery
will succeed, the rest will report appropriate LLD error. Only
application prototypes defined in different discovery rules can result
in discovering the same application.

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