sre-patternslisted

# SRE Patterns Best practices for building and operating reliable systems using Site Reliability Engineering principles. ## SLO / SLI / SLA Definitions These three concepts form the foundation of SRE. They are distinct and frequently confused. | Concept | Definition | Owner | Example | |---------|-----------|-------|---------| | **SLI** (Service Level Indicator) | A quantitative measurement of a service attribute | Engineering | 99.2% of requests completed in < 300ms | | **SLO** (Service Level Objective) | A target value or range for an SLI | Engineering + Product | 99.5% of requests must complete in < 300ms | | **SLA** (Service Level Agreement) | A contract with consequences for missing an SLO | Business + Legal | 99.9% uptime or customer receives service credits | ### Relationship ``` SLI (what you measure) --> SLO (what you target, always stricter than SLA) --> SLA (what you promise externally, with penalties) ``` **Key rule:** SLO must be stricter than SLA. If your SLA promises 99.9% uptime, your internal SLO should target 99.95%. The gap is your safety margin. ## SLI Specification SLIs must be precise, measurable, and tied to user experience. Vague indicators lead to meaningless objectives. ### SLI Types by Service Category | Service Type | SLI Category | Good Event | Valid Event | |-------------|-------------|------------|-------------| | Request-driven | Availability | Response status < 500 | All HTTP requests | | Request-driven | Latency | Response time