Although monitoring itself is a very broad term and as a job may include a lot of activities, there are basically two sides to what a web service monitoring constitutes. Graphing values from sensors is important as a tool to make strategic decisions based on visually apparent trends and also a post factum investigation and sometimes even as a forensics tool. The other side is alerting, which allows administrators to react to incidents as quickly as possible, preventing business consequences. All major monitoring solutions include alerting subsystems and even the toy monitoring script that we built earlier in this chapter is basically a simple alerter.
The http_stub_status module provides scarce information, but it can still be used to quickly react to incidents. These are some good values that can be used to detect unusual conditions requiring immediate attention:
The incoming request rate is a global indicator of the load to your website. Sudden spikes indicate a surge...