SLI, SLO, SLA (service level indicator/objective/agreement)

Key Definitions & Differences

• SLI (Service Level Indicator): The actual measurement of a service's behavior, such as uptime or request success rate.
• SLO (Service Level Objective): A target value for the reliability of a service, defined by the SLI. These are usually internal goals.
• SLA (Service Level Agreement): A contract between a provider and customer that outlines expected service levels and consequences (like service credits) if targets are missed.

Practical Example

• SLI: The current success rate of user logins is 99.98%
• SLO: The goal is 99.95% success rate per month.
• SLA: If success falls below 99.90%, the company owes customers a refund. 

Key Takeaways

• SLOs should be stricter than SLAs to provide a buffer for error.
• SLIs (indicators) are used to measure SLOs (objectives).
• SLAs are typically legally binding and external, while SLOs are internal targets. 

Reference: https://www.atlassian.com/incident-management/kpis/sla-vs-slo-vs-sli