An SLO, or Service Level Objective, is an internal reliability target that a team sets for their service. SLOs are typically stricter than SLAs — if your SLA promises 99.9% uptime, your SLO might target 99.95% to provide a safety buffer.
SLOs are the cornerstone of Site Reliability Engineering (SRE) practice. They provide a framework for making trade-off decisions: when the service is well within its SLO, teams can ship features faster; when the error budget is nearly exhausted, teams should prioritize reliability work.
A well-defined SLO includes the SLI (what you measure), the target (the threshold), and the measurement window (typically 30 days rolling). For example: "99.95% of HTTP requests return a successful response within 500ms over a 30-day rolling window." Monitoring tools like Hyperping provide the SLI data needed to track SLO compliance.
