SLA / SLO / SLI

What Are SLA, SLO, and SLI?

These three terms form the foundation of modern service reliability. They define, measure, and communicate how reliable an IT service is – internally for engineering teams and externally for customers and partners.

SLI – Service Level Indicator

An SLI is a concrete, measurable metric that quantifies an aspect of service quality. Examples: availability percentage, response time in milliseconds, error rate per request. SLIs are the raw data from which SLOs are derived.

SLO – Service Level Objective

An SLO defines the target value for an SLI. Example: "99.9% of requests are answered within 200 ms." SLOs are internal targets that the engineering team strives for. They are deliberately stricter than SLAs to create a buffer.

SLA – Service Level Agreement

An SLA is a contractual agreement between provider and customer that defines minimum service levels and consequences for non-compliance. SLAs are based on SLOs but are legally binding and include compensation provisions.

Error Budgets

The error budget concept complements SLOs: if your SLO is 99.9% availability, you have a budget of 0.1% downtime. Per month, that is approximately 43 minutes. As long as the budget is not exhausted, teams can deploy new features. When the budget is spent, the focus shifts to stability.

Defining SLIs Correctly

• Choose SLIs that are relevant from the user perspective
• Limit to 3–5 per service
• Use percentiles (P95, P99) instead of averages for latencies
• Capture SLIs automatically via monitoring systems like Prometheus

SLOs in Practice

SLOs are not rigid values but are iteratively adjusted. Google recommends starting with an SLO that reflects current performance and then gradually tightening it. SLO dashboards in Grafana make the status transparent for all teams.

SLA Management for Mid-Market Companies

For mid-market companies, thoughtful SLA management is critical: it builds customer trust, gives engineering teams clear priorities, and enables data-driven decisions about feature development vs. stability work.

Why devRocks?

We help you define SLIs, SLOs, and SLAs that fit your services and business requirements. From metric implementation to error budget policies to SLA dashboards, we build a reliability culture in your team.