From Theory to Running SLOs#

Every SRE resource explains what SLOs are. Few explain how to actually implement them from scratch – the Prometheus queries, the error budget math, the alerting rules, and the conversations with product managers when the budget runs out. This guide covers all of it.

Step 1: Choose Your SLIs#

SLIs must measure what users experience. Internal metrics like CPU usage or queue depth are useful for debugging but are not SLIs because users do not care about your CPU – they care whether the page loaded.

SLI, SLO, and SLA – What They Actually Mean#

An SLI (Service Level Indicator) is a quantitative measurement of service quality – a number computed from your metrics. Examples: the proportion of successful HTTP requests, the proportion of requests faster than 500ms, the proportion of jobs completing within their deadline.

An SLO (Service Level Objective) is a target value for an SLI. It is an internal engineering commitment: “99.9% of requests will succeed over a 30-day rolling window.”