Black Box Monitoring – Monitoring the behaviour of a system as a user would see it.

White Box Monitoring – Monitoring based on metrics exposed by the internals of the system, including logs, interfaces like the Java Virtual Machine Profiling Interface, or an HTTP handler that emits internal statistics.

We can extend these principles to Black Box and White Box diagnostic data capture.

We need to extend these definitions further.  The Black Box concept needs to include a service underpinning an application.  For example, the AppSense solution for Citrix comprises its own app server and a database.  Typically, in the first iteration of an investigation we would treat this as a black box.  White Box activity allows us to drill into the AppSense solution.

This raises the point that, although SRE principles imply a user is human, we need to extend the term user to cover other client computer processes.