What are SLA, SLO, and SLI?

• SLI (Service Level Indicator) — a metric that measures the quality of the service provided from the customer's perspective.
  • Examples: error rate, latency, throughput.
• SLO (Service Level Objective) — a target value or range for one or more SLIs. It defines the desired level of service performance.
  • Example: 99.9% of requests should complete without errors 99% of the time.
• SLA (Service Level Agreement) — a formal agreement between the service provider and the customer, defining the SLO and the consequences (e.g., compensation) for its breach.
  • Example: if the service availability drops below 99%, the customer is entitled to a discount.

The relationship between them: SLA includes SLOs, which are based on SLIs. SLIs are used to measure how well the SLOs are being met, and SLOs are part of a legally binding agreement within the SLA.