SLA, SLO, SLI — Explained with Examples

SLA (Service Level Agreement) is a formal contract between a provider and a customer that specifies the expected level of service, usually including penalties for breaches. SLO (Service Level Objective) is an internal target for a reliability metric. SLI (Service Level Indicator) is the actual measured metric — the raw data point.

SLIs are concrete measurements: request latency, error rate, throughput, uptime percentage. SLOs define thresholds for SLIs (e.g., “99.9% of requests complete under 200ms”). SLAs are the legal wrapper around SLOs, often with financial terms. A typical SaaS SLA might promise 99.9% uptime; if the provider falls below, customers get service credits.

Real-world analogy. SLI is your car’s speedometer reading 63 mph. SLO is your personal rule: “I will stay under 70 mph.” SLA is the speed limit law: the government mandates ≤65 mph on this highway, and if you exceed it, you pay a fine. You set your SLO (70) below the SLA (65? no — you’d set it lower to be safe).

Example calculation:

SLI (uptime) = (total minutes - downtime) / total minutes * 100
SLO = 99.9% uptime per month
SLA = 99.9% uptime, credits if below

Related terms: Observability, Chaos Engineering, Zero Downtime Deployment, CI/CD, Canary Deployment

Related tutorial: SLO Management Guide