SLI / SLO / SLA
In depthConcept
Also known as: Service Level Indicator, Service Level Objective, Service Level Agreement
Measurable indicators (SLI), objectives (SLO) and agreements (SLA) about how reliable a service is.
SLI / SLO / SLA, explained
Written by EduVerseWhat it is
Three related terms for talking about reliability. An SLI is a measurement, such as the share of requests that succeed or how fast they’re answered. An SLO is the internal target for that number, and an SLA is the promise in a contract with customers, usually with consequences if it’s broken.
Why teams use it
“The site should be fast and up” isn’t something you can check. These terms turn reliability into numbers that a team can measure, alert on and discuss calmly. The SLO is normally stricter than the SLA, so the team notices trouble before a contractual promise is at risk.
An example from work
Your team agrees that 99.9 percent of login requests in a 30-day window should succeed within one second. After Tuesday’s release a dashboard shows that number sliding, and the team rolls back before the SLO is missed, long before the customer SLA comes into play.
Our own explanation, not a quote from the book.
In the book
Sentences from The Software Realm, Decoded that mention SLI / SLO / SLA, exactly as printed.
3 more passages about SLI / SLO / SLA in the full book
Read every conversation where SLI / SLO / SLA comes up, with the interactive slides and demos.
Where it fits
Reliability management, commitments to customers
Coverage in the book
Covered in depth: multiple pages with explanations, examples and simulations.
