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Discovery probes and sensors

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Discovery probes and sensors

Discovery probes and sensors perform data collection and update the CMDB.

Note: With each release, patterns are replacing many probes and sensors for Discovery. Consider creating new patterns or editing existing ones if you want to customize what Discovery can find. The information on probes and sensors is intended for customers who are not using patterns yet and for customers who already have customized probes that are retained upon upgrade. See Patterns and horizontal discovery for more information on patterns.
Warning: DO NOT switch from probes to patterns if you are already running Discovery with probes, and your CMDB is already populated. If you do so, it is possible that the pattern Discovery process does not synchronize on the same values that the probe Discovery process does. This could result in duplicate CIs in your CMDB.

Discovery phases

Discovery always uses probes and sensors during the first two phases of discovery: scanning and classification. For the last two phases, identification and exploration, Discovery can use probes and sensors or patterns. This topic refers to probes and sensors only. See Discovery basics for an explanation of these phases. See Patterns and horizontal discovery for more information on patterns.

Probes, sensors, and the ECC queue

The probe collects the information and the sensor processes it. Both get their instructions from the ECC queue. There is a worker job on the MID Server that monitors the queue for work. The monitor checks for any entries where the Queue is output and the State is ready.
The ECC queue
The MID Server then processes all the output ECC messages, runs the necessary probes, and returns the probes results to the ECC queue. These results are put in the ECC Queue as input entries.
Figure 1. ECC queue input
ECC queue record

After an entry is inserted in the ECC Queue table, a business rule fires (on insert) that takes that information and runs it through a sensor processor. The sensor processor's job is to take the input data, find any sensors interested in that data, and pass it along to be processed. Those sensors ultimately update the CMDB.

How probes and sensors work together

The MID Server launches probes to collect information about a device. The probe sends back information to the sensor to be processed. If the probe has a post-processing script defined, the post-processing script does some data processing on the MID Server before data is sent back to the sensor on the ServiceNow instance. Otherwise the probes sends back all the data collected and the sensor performs this data processing. In both cases, the sensor updates the CMDB.

A multi-probe is a probe that contains probes. A multi-sensor processes the data from a multi-probe. To process the data from the multi-probe, the multi-sensor contains individual scripts to process the data returned by each probe contained in the Multiprobe, as well as a main multi-sensor script. The individual scripts pass their processed data to the main multi-sensor script.

The MultiSensor form

Probe types

Device Probe Type
Windows computers and servers Remote WMI queries, shell commands
UNIX and Linux servers Shell command (via SSH protocol, version 2). Discovery supports any Bourne-compatible shell.
Storage CIM/WBEM queries
Printers SNMP queries
Network gear (switches, routers, etc.) SNMP queries
Web servers HTTP header examination
Uninterruptible Power Supplies (UPS) SNMP queries