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DevOps & Automation · Foundational

Service Level Indicator (SLI)

A quantitative measure of some aspect of a service's level of service, such as request latency, error rate, or availability.

Definition

An SLI is usually expressed as a ratio of good events to total events over a time window, for example the proportion of HTTP requests served successfully in under 300 ms. SLIs are the raw measurements that SLOs set targets against.

Example

SLI = successful requests with latency < 300 ms / total valid requests, measured over 28 days.

Exam tip

An SLI is the measurement, the SLO is the target, and the SLA is the contract with consequences; do not mix them up.

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