Backend & systems·Observability and operations
you pick the one number that actually represents whether users are having a good time, like the fraction of requests under 300ms.
Service level indicator
Also calledSLI
A measured quantity representing service quality, usually a ratio of good events to total events. The choice is the hard part: it must correlate with user experience, not with system internals. CPU utilisation is not an SLI; successful checkout rate is.