The difference between active and passive monitoring and why you actually need both.

This article looks at the difference between active and passive monitoring and explains how the two together take IT service management to the next level.

We are often asked by our clients about the different methods that exist for monitoring. Basically, you have to distinguish between passive and active monitoring. You can find good descriptions of these two methods on Wikipedia:

https://de.wikipedia.org/wiki/End_to_End_Monitoring
https://en.wikipedia.org/wiki/Real_user_monitoring

First read the pros and cons of both methods. A summary follows at the end.

Active monitoring

Active monitoring, also known as active testing, involves software robots simulating the behaviour of the end user. Solutions for active monitoring are easier to implement than those for passive monitoring - but you won't find many companies offering this service. Only a few systems (probes or measuring robots) are needed as infrastructure. These operate an application exactly as a real end user would. The user processes are implemented in the form of scripts, i.e. at regular intervals certain user actions are executed controlled by scripts, for example for visiting a web page in online banking. The scripts must be developed and maintained. In addition, a central collection and evaluation system is needed. However, changes to existing systems and applications are not necessary.

Active monitoring has some real advantages, especially the controlled environment that provides consistent results. Here, the same user activities are carried out in the same way on a regular basis. Active monitoring provides (reference) values and a wealth of timing information that you would not get with passive monitoring.

What has always "bothered" me personally about active monitoring is the fact that it only monitors and displays the performance of specific applications/sites at specific locations. To get better coverage, tests have to be done at multiple sites, which in turn increase the amount of additional ("artificial") traffic and system load. Even if you greatly expand the monitoring geographically and functionally, you still do not achieve a fully realistic coverage of what end users see. The alternative or a useful addition can therefore be passive monitoring.

Passive monitoring

With passive monitoring, the measurement takes place directly at the end user's system. For this, additional software must be installed and configured - and this on many systems in the backend (server) and also in the frontend (PC/client) area. Only then can monitoring data be collected and analysed. In contrast to active monitoring, neither additional (artificial) data traffic nor system load is generated. One receives complete information about what the real users see in the applications or on websites and what the real response times are.


One disadvantage of passive monitoring is that you can only measure when the end users are actually working. On weekends, holidays and at night, the availability and performance of the applications are therefore not monitored. Only the first end user who uses the application after such a "rest period" notices if something is wrong.

Can we do better?

Several clients have asked for a single monitoring tool to perform recurring, automated tests for application performance as well as availability. I am not convinced that this is the right way to go. Instead, I prefer a healthy mix of passive and active monitoring. This way you get a 360° view and at the same time reduce the system load. You achieve this by adjusting and optimising active tests based on information from passive monitoring (such as the top pages of a day or pages that are working slower or faster than normal).

The big benefit for a company

In fact, the greatest benefit is achieved by combining the two methods, namely a 360° view of all components involved: Passive monitoring provides the users' view, active monitoring provides the (reference) values around the clock, 365 days a year, even when the end users are not using the applications. Changes in the performance of the applications become immediately visible.

Discussion - How do you handle it?

We would like to hear from you how you monitor your applications/websites and what experiences you have gained.