Introduction to real-time eventlog monitoring

NSClient++ has a very powerful component that enables you to achieve real-time eventlog monitoring on Windows systems. This feature requires passive monitoring of Windows eventlogs via NSCA or NRDP.

The biggest benefits of real-time eventlog monitoring are:

  • It can help you find problems faster (real-time), as NSClient++ will send the events with NSCA the moment it occurs.
  • It is much more resource efficient then using active checks for monitoring eventlogs. It actually requires fewer resources on both the Nagios server, as on the client where NSClient is running!
  • There is no need to search through every application’s documentation, as you can just catch all the errors and filter them out if not needed.

The biggest drawbacks of real-time eventlog monitoring are:

  • As it are passive services, new events will overwrite the previous event, which could cause you to miss a problem on your Nagios dashboards. 
  • You need  a dedicated database table to store the real-time eventlog exclusions. 
  • You will need some basic scripting skills to automate building the real-time eventlog exclusion string in the NSClient configuration file.

General requirements for using real-time eventlog monitoring

NSCA Configuration of your NSClient++

As NSClient++’s real-time eventlog monitoring component will send the events passively to you Nagios server, you will need to setup NSCA. Please read through this documentation for configuring NSCA in NSClient++.

NSCA Configuration of your Nagios server

NSCA also requires some configuration on your Nagios server. Please read through this documentation for configuring NSCA in Nagios Core or this documentation for configuring NSCA in Nagios XI.

Passive services for each Windows host on your Nagios server

Each Windows host needs at least one passive service, which is able to accept the filtered Windows eventlogs. You can make as much of them as you require. I choose to use one for all application eventlog errors and one for all system eventlog errors:

Real-Time Eventlog Monitoring Passive Services

A database to store your real-time eventlog exclusions

If you want to generate a real-time eventlog exclusion filter, you need to somehow store a combination of hostnames, event id’s and event sources. We are using MSSQL at the moment and generate the exclusions with Powershell. This database needs at least a servername, eventlog, eventid, eventsource and comment column. The combination of those allow you to make an exclusion for almost any type of Windows event.

Real-time Eventlog Monitoring Exclusion Database

Some sort of automation software which can be called with a Nagios XI quick action

Thanks to Nagios XI quick actions, you can quickly exclude noisy events by updating the NSClient++ configuration file with the correct filter. With the correct customization and scripts, this allows you to create a self-learning system. For this to work, you basically need one script which will store a new real-time eventlog exclusion in a database and another which generates the NSClient++ configuration file with the latest combination of real-time eventlog exclusions. We are using Rundeck, a free and open source automation tool to execute the above jobs.

Detailed NSClient ++ configuration

Minimal nsclient.ini ‘modules’ settings:

Minimal nsclient.ini ‘NSCA’ settings:

The above configuration doesn’t use any encryption. Once your tests work out, I advise you to configure some sort of encryption to prevent hackers from sniffing your NSCA packets. Please note that at this moment (31/05/17) the official Nagios NSCA project does not support aes, only Rijndael. This GitHub issue has been created to fix this problem. You’ll have to use one of the other less strong encryption methods at the moment.

Example nsclient.ini ‘eventlog’ settings:

This is an example configuration for getting real-time eventlog monitoring to work. Please note that this has been tested on NSClient++ I’m not 100 % sure it works on earlier versions.

The above configuration template is just an example. As you can see it contains a DUMMYAPPLICATIONFILTER and a DUMMYSYSTEMFILTER. You can easily replace these with the generated exclusion filter. A few examples of how such a filter might look:

(id NOT IN (1,3,10,12,13,23,26,33,37,38,58,67,101,103,104,107,108,110,112,274,502,511,1000,1002,1004,1005,1009,1010,1026,1027,1053,1054,1085,1101,1107,1116,1301,1325,1334,1373,1500,1502,1504,1508,1511,1515,1521,1533)) AND (id NOT IN (1509) OR source NOT IN ('Userenv')) AND (id NOT IN (1055) OR source NOT IN ('Userenv')) AND (id NOT IN (1030) OR source NOT IN ('Userenv')) AND (id NOT IN (1006) OR source NOT IN ('Userenv')) 


(id NOT IN (1,3,4,5,8,9,10,11,12,15,19,27,37,39,50,54,56,137,1030,1041,1060,1066,1069,1071,1111,1196,3621,4192,4224,4243,4307,5722,5723)) AND (id NOT IN (36888) OR source NOT IN ('Schannel')) AND (id NOT IN (36887) OR source NOT IN ('Schannel')) AND (id NOT IN (36874) OR source NOT IN ('Schannel')) AND (id NOT IN (36870) OR source NOT IN ('Schannel')) AND (id NOT IN (12292) OR source NOT IN ('VSS')) AND (id NOT IN (7030) OR source NOT IN ('ServiceControlManager')) 

Only errors which are not filtered by the real-time eventlog filters such as the examples above will be sent to your Nagios passive services.

Multiple NSCA Targets

This is an nsclient.ini config file where two NSCA targets are defined. This can be useful in scenarios where a backup Nagios server needs to be identical as the primary Nagios server:

How to generate errors in your Windows eventlogs?

In order to test, you will need a way to debug and hence a way to generate errors with specific sources or id’s. You can do this very easily with Powershell:

If you get an error saying that the source passed with the above command does not exist, you can create it like this:

Or another way:

(Almost) Final Words

As I can hear some people think “why don’t you post the code to generate the real-time eventlog exclusion filter?”. Well, the answer is simple, I don’t have the time to clean up all the code, so it doesn’t contain any sensitive information. But as a special gift for all my blog readers who got to the end of this post, I’ll post a snippet of the exclusion generating Powershell code here. The rest you will have to make your self for now.

I will open the comments section for now, but please only use it for constructive information. 



Willem D'Haese
Expert Monitoring at Digipolis
Expert Monitoring with a demonstrated history of working in the information technology and services industry. Strong ICT skills such as monitoring, virtualization, automation.

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code class="" title="" data-url=""> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong> <pre class="" title="" data-url=""> <span class="" title="" data-url="">