What is Monitoring?

In secondary school, one of Brian's teachers told him that if you were ask 10 economists what economics means, you'd get 11 answers. Monitoring has a similar lack of consensus as to what exactly it means. When he tells others what he does, people think his job entails everything from keeping an eye on temperature in factories, to employee monitoring where he is the one to find out who is acceessing Facebook during working hours. and even detecting intruders on networks.

Prometheus wasn't built to do any of those things. It was built to aid software developers and administrators in the operation of production computer systems, such as the applications, tools, databases, and networks backing popular websites.

So what is monitoring in that contexts? Let's narrow this sort of operational monitoring of computer systems down to four things.

Alerting

Knowing when things are going wrong is usually the most important thing that you want monitoring for. You want the monitoring system to call in a human to take a look.

Debugging

Now that you have callled in a human, they need to investigate to determine the root cause and ultimately resolve whatever the issue is.

*Trending *

Alerting and debugging usually happen on timescales on the order of minutes to hours. While less urgent, the ability to see how your systems are being used and changing over time is also useful. Trending can feed into design decisions and processes such as capacity planning.

Plumbing

When all you have is a hammer, everything starts to look like a nail. At the end of the day, all monitoring systems are data processing pipelines. Sometimes it is more convenient to appropriate part of your monitoring system for another purpose, rather than building a bespoke solution. This is not strictly monitoring, but it is common in practice so we like to include it.

Depending on who you talk to and their background, they may consider only some of these to be monitoring. This leads to many discussions about monitoring going around in circles, leaving everyone frustrated. To help you understand where others are coming from, we're going to look at a small bit of the history of monitoring.