Discovery probes and sensors

Discovery probes and sensors perform data collection and update the Configuration Management Database (CMDB).

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.

Note:

For information on Probe to Pattern migration see the knowledge article KB0694477.

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 Exploring Discovery 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 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

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.

Important:

Discovery now enforces code signing for probes, probe parameters, and sensors when code signing is enabled on the instance. Unsigned or tampered payloads are blocked, and signatures are validated before execution. For more information about code signing, see Discovery on Code Signing instances.

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.

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

• List of Discovery probes
  A wide variety of probes exist for the Discovery application to detect elements on your network.
• Discovery sensors
  Every probe in Discovery must have a corresponding sensor to process the data returned.
• Discovery probe management
  Several discovery probes and their associated sensors are included with Discovery. You rarely need to modify probes or sensors. But you might need to set parameters to control the behavior of a particular probe or align versions of customized probes.
• Align versions of customized probes and sensors
  If you customized a probe or sensor and upgraded to a new version of an instance, you need to realign the versions of the customized probe and sensor to the most current version.
• Discovery multiprobes and multisensors
  Multiprobes contain one or more simple probes configured to extract specific information from manageable devices by executing multiple queries with a single authentication.
• Example: Custom Discovery probe to populate a CI from a text file
  This custom Discovery probe reads a text file from a Windows computer and populates a configuration item (CI) in the CMDB with the values from the file.