What is Service Level Objectives (SLOs)?
Service Level Objectives (SLOs) are specific, measurable targets for service reliability that define how reliable a service should be.
Service Level Objectives (SLOs) are specific, measurable targets for service reliability that define how reliable a service should be. They are the foundation of Site Reliability Engineering (SRE) and modern operations practices.
Hierarchy: - SLI (Service Level Indicator): The metric (e.g., request latency, availability %) - SLO (Service Level Objective): The target for the SLI (e.g., 99.9% availability) - SLA (Service Level Agreement): The contractual commitment to customers (usually looser than the SLO) - Error Budget: The acceptable amount of downtime before action is required
Key insight: 99.9% availability ≠ 99.99% availability. The difference is 8.7 hours vs 52.6 minutes of downtime per year — a 10x difference in engineering investment.
Why It Matters
SLOs create a data-driven framework for reliability investment decisions. Without SLOs, reliability decisions are political ("everything must be 100% available") or reactive ("fix it after it breaks"). SLOs enable economic analysis of reliability investments.
Frequently Asked Questions
What is an error budget?
An error budget is the acceptable amount of unreliability over a time period, derived from the SLO. If your SLO is 99.9% availability monthly, your error budget is 43.8 minutes of downtime. When the budget is exhausted, teams shift from feature work to reliability work.
Related Terms
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