Discovery Probes and Sensors

Discovery Probes and Sensors

Introduction

Discovery is a module that servicenow provides in order to maintain CI's data that are present in the network of an organization. It is an automated process which means you just need to configure this and it will work on it's own i.e mannual intervention is not required ( given nothing is going wrong and you have configured it as expected) .

The basic functionality of discovery is to knock the door of each and every device that are present in your network. Then classify which kind of device it is ex. computer, server etc. Then gathers the detailed information of the device like Serial number, Version and so on and populates all these data into the cmdb_ci table.

 Now the one who is responsible for knocking the doors and gathering data is what is called Probe and the one who is responsible for analyzing these data and populating cmdb_ci table is what is called Sensor. The one who does the coordination between the servicenow and client network is called the MidServer (we are not discusign midserver in this post).

Now, since we have some basic understanding of what is probe and sensor, let's go in depth of it. We will start with Probe first.

Probes

The best way to understand probe and sensor is with an example of Survey. In a survey what happens, we choose few people and provide some set of questions to them that is to be asked from common people. Then the agent goes into the market knocks all the relevant doors, asks all the questions given to them and notes down all the responses that comes in. Then they brings those results back to you. You hand over all those data to the analysis team who analyses the data and decides what to do and finally changes are made in the the product based on that. Similar thing happens when discovery runs.

Lets look at it now from discovery point of view. 

Your survey here is Discovery.

People who where chosen to do survey is Probe.

People who analyses the data and make changes is Sensor.

Now let's understand what is probe and what are it;s role from servicenow point of view.

Probe is a module in servicenow under Discovery definition application. Probe contains the question that needs to be asked from the devices that are present in the network. Following are the information carried by a probe :-

1. The type of probe it is i.e. window/linux/snmp etc.

2. Where will it execute like cmd / powershell / ssh etc.

3. Content that it will execute ex. command like uname / ipconfig / powershell script etc.

Once probe gets launched it goes directly to the midserver. Midserver takes the script/command that needs to be executed and executes on the devices ( identified by IP addresses ). Once this execution gets completed midserver hands over the result to the probe. Probe comes back to the servicenow tool and hands over the result to the sensor for further processing.


NOTE - For each and every probe there must be a sensor defined else it will raise an error "no sensor defined" .


Below is the diagramatic representation of working of probe.

Sensor

When probe returns to the servicenow tool with the desired result the job of sensor comes into play. Corresponding to every probe there exists a sensor. The job of the sensor is to process the data that is returned by their corresponding probe and then populating the processed data to the CI table.

I hope you find this article informative. Please give your feedback into the comments.

Thank you