Building a Circuit Breaker in Rust: From Zero to Production

Your service calls an external API. It goes down. Your threads pile up waiting for timeouts. Your whole app dies. The Circuit Breaker pattern exists to prevent exactly this. What We're Building A production-grade Circuit Breaker with three states, configurable thresholds, and zero unsafe code. ┌─────────────────────────────────┐ │ │ failures >= threshold call succeeds │ │ ┌───────────────▼──────────┐ ┌────────────┴─────────┐ │ │ │ │ │ CLOSED │ │ HALF-OPEN │ │ (requests pass through)│ │ (one probe call) │ │ │ │ │ └──────────────────────────┘ └───────────────────────┘ ▲ │ │ call fails│ │ ▼ │ ┌────────────────────────┐ │ │ │ │ timeout expires │ OPEN │ └──────────────────│ (requests rejected) │ │ │ └────────────────────────┘ Three states: Closed — normal operation, requests flow through, failures are counted Open — service is assumed down, requests are rejected immediately (fail fast) Half-Open — after a timeout, one probe request goes through to check recovery Step 1 — Model the State Mac