Service Level Objective
Internal target for service reliability and performance
A Service Level Objective is an internal target for service reliability, availability, or performance that guides engineering priorities and operational decisions. While SLAs are external customer commitments, SLOs are internal goals typically more aggressive than SLAs, providing buffer before violating customer agreements. SLOs define specific measurable targets like ninety-nine point nine five percent availability, ninety-five percent of requests under two hundred milliseconds, or ninety-nine percent of support tickets responded within one hour. These objectives reflect what teams believe is appropriate reliability level balancing user needs with development velocity. The SLO framework includes Service Level Indicators which are metrics measuring service health, Service Level Objectives which are target values for those indicators, and Error Budgets which are allowed unreliability calculated from SLOs. For example, ninety-nine point nine percent availability SLO means forty-three minutes monthly downtime are acceptable error budget. SLOs provide multiple benefits: clear reliability targets guiding priorities, quantified tradeoffs between reliability and velocity, objective data for decisions, error budgets enabling innovation, and accountability for service health. Teams monitor SLO achievement continuously, using error budget consumption to guide decisions. When error budget remains, teams can move fast and take risks. When exhausted, reliability work takes priority. Setting effective SLOs requires understanding user expectations and impact, analyzing historical performance, defining meaningful indicators, setting achievable but aspirational targets, and gaining stakeholder alignment. Best practices include starting with few critical SLOs, making them user-centric not system-centric, measuring accurately, reviewing regularly, and taking action when violated. Common mistakes include too many SLOs creating confusion, too aggressive targets causing stress, inadequate measurement, or ignoring violations. Product managers should understand SLOs, support reliability investments when needed, balance feature pressure with reliability, and use error budgets in prioritization discussions. Strong SLO practice creates shared language for reliability discussions and enables data-driven decisions balancing innovation with stability.
Learn about Service Level Objectives in SRE. Discover how internal reliability targets guide engineering priorities and error budgets.