Reliability · Flashcard
What is a Service Level Indicator (SLI)?
- AA quantitative measure of a service level — such as the proportion of requests served successfully or fast enough
- BA target value a service should meet — such as 99.9% of requests succeeding over a rolling 28-day window
- CA contract with customers that sets financial penalties — such as refunds when uptime falls below a threshold
- DA remaining allowance of unreliability — such as the number of failed requests a team may spend before freezing
Why this is the answer
An SLI is what you measure: a metric like the ratio of good events to valid events (e.g. successful or fast requests). A target value is the SLO, not the indicator itself. A customer contract with penalties is the SLA. A remaining allowance of unreliability is the error budget. The SLI is only the measurement the other three are built on.
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