What are SLOs and SLIs?

Short answer

A Service Level Indicator (SLI) is a quantitative measure of service quality. A Service Level Objective (SLO) is the target value for that SLI over a period.

How it works

Common SLIs include availability, latency, and error rate. The SLO defines the acceptable threshold, such as 99.9% availability. The error budget is the remaining room for failure.

Example

SLI: Request latency < 200ms
SLO: 99% of requests < 200ms over 30 days
Error budget: 1% of requests may exceed 200ms

Why it matters

SLOs align engineering and business expectations. They guide prioritization and justify investment in reliability.

Tips

• Start with a few critical SLIs.
• Involve stakeholders in SLO definition.
• Use error budgets to balance velocity and stability.

Common issues

• Overly aggressive SLOs waste engineering effort.
• Under-measured SLIs provide false confidence.
• Missing SLOs lead to reactive firefighting.