What is Service Level Objective? — UK Software Development Guide
Direct Answer
A Service Level Objective (SLO) is an internal reliability target for a software service — typically more ambitious than the external Service Level Agreement (SLA). SLOs are measured using Service Level Indicators (SLIs): specific, measurable metrics such as request success rate, response latency, or availability percentage. The gap between SLO and 100% reliability is the "error budget" — the allowable amount of unreliability per period.
Slo in the UK
SLOs have UK FCA and NHS relevance. FCA operational resilience (PS21/3) requires firms to define and test impact tolerances — SLOs are the technical expression of these tolerances. NHS DSP Toolkit expects documented availability requirements for clinical software — SLOs provide this documentation. ClickMasters implements SLOs using: Datadog (enterprise) or Prometheus/Grafana (open source) for SLI measurement, automated alerting when error budget burn rate exceeds threshold, and monthly SLO review as part of maintenance retainer services.
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