Reliability & Observability

Reliability is the ability of a system to function correctly even when things go wrong. Observability is the ability to understand the internal state of a system from its external outputs. Together, they ensure you can build systems that work and know when they do not.

---

SLOs, SLIs, and SLAs

┌───────────────────────────────────────────────────────────┐
│                                                            │
│  SLI (Service Level Indicator)                             │
│  "What we measure"                                         │
│  e.g. request latency, error rate, throughput              │
│                                                            │
│  SLO (Service Level Objective)                             │
│  "What we aim for"                                         │
│  e.g. 99.9% of requests complete in < 200ms               │
│                                                            │
│  SLA (Service Level Agreement)                             │
│  "What we promise (with consequences)"                     │
│  e.g. 99.9% uptime or customer gets credits               │
│                                                            │
└───────────────────────────────────────────────────────────┘

Common SLIs