SLO
Service Level Objective: a target value for an SLI, like '99.9% of requests under 300ms.' The internal engineering goal that drives reliability investment.
What is SLO?
Service Level Objective: a target value for an SLI, like '99.9% of requests under 300ms.' The internal engineering goal that drives reliability investment.
SLO is a advanced concept that sits in the Reliability & Resilience area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "SLO" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
Learn SLO in depth
Full interactive lesson with diagrams, code examples, real-world references, and a quiz.
Open the SLO lessonRelated lessons
Lessons that touch on SLO as part of a larger topic.
SLO (Service Level Objectives)
The reliability targets you set for your SLIs, the line between 'acceptable' and 'we need to fix this'
intermediate · observability monitoring
SLA/SLO/SLI Overview
Putting it all together, how SLIs, SLOs, and SLAs work as a unified reliability framework
intermediate · observability monitoring
Error Budget
The quantified amount of unreliability you're allowed, the most powerful tool in SRE
intermediate · observability monitoring
Sloppy Quorum
Relaxed quorum rules that prioritize availability over strict replica placement
advanced · distributed systems core
SLO Engineering
Define and measure Service Level Objectives, the practice that aligns reliability with business needs
advanced · reliability resilience
See also
Related glossary terms you might want to look up next.
SLI
Service Level Indicator: a quantitative measure of service behavior, like the proportion of requests faster than 300ms. The raw metric that feeds SLOs.
SLA
Service Level Agreement: a contractual commitment between provider and customer specifying uptime, response time, and penalties for breaches. The business version of an SLO.
Error Budget
The allowed amount of unreliability derived from SLOs. If your SLO is 99.9% uptime, your error budget is 0.1% (about 43 minutes/month). Once exhausted, freeze deployments.