vercel-reliability-patterns

# Vercel Reliability Patterns ## Overview Build fault-tolerant Vercel deployments with circuit breakers, retry logic, graceful degradation, and instant rollback integration. Addresses reliability at two levels: function-level resilience (protecting against dependency failures) and deployment-level resilience (protecting against bad deploys). ## Prerequisites - Vercel project deployed to production - Understanding of failure modes in serverless - External dependencies (databases, APIs) identified ## Instructions ### Step 1: Circuit Breaker for External Dependencies ```typescript // lib/circuit-breaker.ts type CircuitState = 'CLOSED' | 'OPEN' | 'HALF_OPEN'; class CircuitBreaker { private state: CircuitState = 'CLOSED'; private failures = 0; private lastFailure = 0; private readonly threshold: number; private readonly resetTimeMs: number; constructor(threshold = 5, resetTimeMs = 30000) { this.threshold = threshold; this.resetTimeMs = resetTimeMs; } async call<T>(fn: () => Promise<T>, fallback: () => T): Promise<T> { if (this.state === 'OPEN') { if (Date.now() - this.lastFailure > this.resetTimeMs) { this.state = 'HALF_OPEN'; } else { console.warn('Circuit OPEN — returning fallback'); return fallback(); } } try { const result = await fn(); this.onSuccess(); return result; } catch (error) { this.onFailure(); console.error('Circuit breaker caught error:', error); ...