Service Level Objectives

# Service Level Objectives

You can't improve reliability without measuring it. SLOs provide the framework.

## The Stack

**SLI (Service Level Indicator)**

What you measure. Latency, error rate, throughput.

**SLO (Service Level Objective)**

Your target. "99.9% of requests succeed."

**SLA (Service Level Agreement)**

Contract with users. Usually has financial penalties.

## Choosing Good SLIs

**User-Focused**

Measure what users care about, not what's easy to measure.

**Request Success Rate**

Most fundamental metric. Did it work?

**Request Latency**

How fast? P50, P95, P99.

**Availability**

Is the service up?

## Error Budgets

**100% Uptime is Wrong**

Perfect reliability prevents innovation.

**Error Budget = 1 - SLO**

99.9% SLO = 0.1% error budget = 43 minutes/month.

**Use Your Budget**

Spend it on features. When exhausted, focus on reliability.

## Implementing SLOs

- Start with loose SLOs

- Measure continuously

- Review and adjust

- Automate alerting

SLOs align engineering with user needs.