Learning PowerShell DSC - Second Edition

Idempotence

Idempotence is an important concept, sometimes confusing, that we will touch on many times throughout this book. Idempotence is defined as an operation that has no additional effect if it is called more than once with the same input. Put another way, it is an operation that can be executed as many times as desired, and it will only change the system state if, and only if, it is not what the desired state is. For example, a PowerShell function looks for the x state and guarantees that it will only change the state of the system if it is not x.

It may seem silly to state something as obvious as this. If you feel this way, think of an MSI installer that installs version 1.1.1.0 of an imaginary software product. When you run the MSI, ...