Issue
Overview
How discovery identification engine works while identifying for existing Cis and takes a decision on whether to create new CI or updates the existing one.
Discovery identification matching process
Discovery tries to find if an existing entry in found in the CMDB by looking at identification rules. We will take an example of Hardware Rule:
https://<instance_name>.service-now.com/nav_to.do?uri=cmdb_identifier.do?sys_id=a1d19344c3b33100d8d4bea192d3aedc
The matching process occurs from top to bottom, lowest priority first.
Rule 1 is the topmost rule with serial_number and serial_number_type.
The search will be on the cmdb_serial_number table.
There are two possibilities in this scenario:
Case 1: The discovery payload contains serial_number and serial_number_type
In this case, the Identification engine searches the table cmdb_serial_number for the match and again it will have two more possible outcomes:
Match found: It will ignore the other rules with priorities 200, 300 and 400 in this example and updates the respective CI.
Identifier: Hardware Rule, Rule 1 Searched on <cmdb_serial_number> for attributes: serial_number,serial_number_type:Match.
Match not found: It will continue with next higher order rules and continues until a match is found.
Identifier: Hardware Rule, Rule 1 Searched on <cmdb_serial_number> for attributes: serial_number,serial_number_type:No Match.
Case 2: Discovery payload doesn't contain either serial_number or serial_number_type fields.
In this case, it will show up a message in discovery logs stating, "Skipped Identifier entry" and continues to next rule.
Identifier: Hardware Rule, Rule 1 Searched on <cmdb_serial_number> for attributes: serial_number,serial_number_type:Skipped Identifier Entry.
This process continues until the match is found on the tables defined in Identifier rules. If there is no match found after running all the rules, then it will create a new CI.
Additional Information
This youtube video provides complete information regarding the discovery identification process:
