When you manage and develop infrastructure, you'll work with tests and monitoring solutions that ensure the quality of your end product (code or infrastructure). For code quality, you can have unit tests, functional tests, and integration tests etc.  Similarly, you might have system monitoring, dependancy monnitoring, application monitoring, BAM, CEP, etc. In this post I'll narrate few of them:

1. System monitoring : Watches CPU load, free memory (RAM), disk space etc. SNMP based hardware monitoring, etc.
2. Dependency monitoring : Checks web server processes, web server states , %CPU consumption, RSS, etc.
3. Integration : Tracks third party or other integration points whether they are available or not.
4. BAM : Business activity monitoring. Records KPI or key performance indicators, which will in turn define the state of your business (quantitatively). This could include sucessful transactions per day or month.
5. Process instrumentation or tracing : Includes kprobes, system tap, or other tracing like methodologies like DTrace, which lets you monitor at the individual method level. These are predominantly used for language or other interpreter optimizations.
6. Complex event processing : Though not directly related, some of these monitoring solutions can or should use some form of complex event processing to deduce meaningful information. This is only important (or even significant) if the volume of data is large.

Depending upon your problem you should employ one of more of these solutions. There are plenty of open source solutions/tooling available for all of them. BAM is kinda tricky, not BAM in itself, but defining the KPI part is bit trippy.