Vercel Reliability Patterns

Overview

Production-grade reliability patterns for Vercel integrations.

Prerequisites

• Understanding of circuit breaker pattern
• opossum or similar library installed
• Queue infrastructure for DLQ
• Caching layer for fallbacks

Circuit Breaker

import CircuitBreaker from 'opossum';

const vercelBreaker = new CircuitBreaker(
  async (operation: () => Promise<any>) => operation(),
  {
    timeout: 10000,
    errorThresholdPercentage: 50,
    resetTimeout: 30000,
    volumeThreshold: 10,
  }
);

// Events
vercelBreaker.on('open', () => {
  console.warn('Vercel circuit OPEN - requests failing fast');
  alertOps('Vercel circuit breaker opened');
});

vercelBreaker.on('halfOpen', () => {
  console.info('Vercel circuit HALF-OPEN - testing recovery');
});

vercelBreaker.on('close', () => {
  console.info('Vercel circuit CLOSED - normal operation');
});

// Usage
async function safeVercelCall<T>(fn: () => Promise<T>): Promise<T> {
  return vercelBreaker.fire(fn);
}

Idempotency Keys

import { v4 as uuidv4 } from 'uuid';
import crypto from 'crypto';

// Generate deterministic idempotency key from input
function generateIdempotencyKey(
  operation: string,
  params: Record<string, any>
): string {
  const data = JSON.stringify({ operation, params });
  return crypto.createHash('sha256').update(data).digest('hex');
}

// Or use random key with storage
class IdempotencyManager {
  private store: Map<string, { key: string; expiresAt: Date }> = new Map();

  getOrCreate(operationId: string): string {
    const existing = this.store.get(operationId);
    if (existing && existing.expiresAt > new Date()) {
      return existing.key;
    }

    const key = uuidv4();
    this.store.set(operationId, {
      key,
      expiresAt: new Date(Date.now() + 24 * 60 * 60 * 1000),
    });
    return key;
  }
}

Bulkhead Pattern

import PQueue from 'p-queue';

// Separate queues for different operations
const vercelQueues = {
  critical: new PQueue({ concurrency: 10 }),
  normal: new PQueue({ concurrency: 5 }),
  bulk: new PQueue({ concurrency: 2 }),
};

async function prioritizedVercelCall<T>(
  priority: 'critical' | 'normal' | 'bulk',
  fn: () => Promise<T>
): Promise<T> {
  return vercelQueues[priority].add(fn);
}

// Usage
await prioritizedVercelCall('critical', () =>
  vercelClient.processPayment(order)
);

await prioritizedVercelCall('bulk', () =>
  vercelClient.syncCatalog(products)
);

Timeout Hierarchy

const TIMEOUT_CONFIG = {
  connect: 5000,      // Initial connection
  request: 30000,     // Standard requests
  upload: 120000,     // File uploads
  longPoll: 300000,   // Webhook long-polling
};

async function timedoutVercelCall<T>(
  operation: 'connect' | 'request' | 'upload' | 'longPoll',
  fn: () => Promise<T>
): Promise<T> {
  const timeout = TIMEOUT_CONFIG[operation];

  return Promise.race([
    fn(),
    new Promise<never>((_, reject) =>
      setTimeout(() => reject(new Error(`Vercel ${operation} timeout`)), timeout)
    ),
  ]);
}

Graceful Degradation

interface VercelFallback {
  enabled: boolean;
  data: any;
  staleness: 'fresh' | 'stale' | 'very_stale';
}

async function withVercelFallback<T>(
  fn: () => Promise<T>,
  fallbackFn: () => Promise<T>
): Promise<{ data: T; fallback: boolean }> {
  try {
    const data = await fn();
    // Update cache for future fallback
    await updateFallbackCache(data);
    return { data, fallback: false };
  } catch (error) {
    console.warn('Vercel failed, using fallback:', error.message);
    const data = await fallbackFn();
    return { data, fallback: true };
  }
}

Dead Letter Queue

interface DeadLetterEntry {
  id: string;
  operation: string;
  payload: any;
  error: string;
  attempts: number;
  lastAttempt: Date;
}

class VercelDeadLetterQueue {
  private queue: DeadLetterEntry[] = [];

  add(entry: Omit<DeadLetterEntry, 'id' | 'lastAttempt'>): void {
    this.queue.push({
      ...entry,
      id: uuidv4(),
      lastAttempt: new Date(),
    });
  }

  async processOne(): Promise<boolean> {
    const entry = this.queue.shift();
    if (!entry) return false;

    try {
      await vercelClient[entry.operation](entry.payload);
      console.log(`DLQ: Successfully reprocessed ${entry.id}`);
      return true;
    } catch (error) {
      entry.attempts++;
      entry.lastAttempt = new Date();

      if (entry.attempts < 5) {
        this.queue.push(entry);
      } else {
        console.error(`DLQ: Giving up on ${entry.id} after 5 attempts`);
        await alertOnPermanentFailure(entry);
      }
      return false;
    }
  }
}

Health Check with Degraded State

type HealthStatus = 'healthy' | 'degraded' | 'unhealthy';

async function vercelHealthCheck(): Promise<{
  status: HealthStatus;
  details: Record<string, any>;
}> {
  const checks = {
    api: await checkApiConnectivity(),
    circuitBreaker: vercelBreaker.stats(),
    dlqSize: deadLetterQueue.size(),
  };

  const status: HealthStatus =
    !checks.api.connected ? 'unhealthy' :
    checks.circuitBreaker.state === 'open' ? 'degraded' :
    checks.dlqSize > 100 ? 'degraded' :
    'healthy';

  return { status, details: checks };
}

Instructions

Step 1: Implement Circuit Breaker

Wrap Vercel calls with circuit breaker.

Step 2: Add Idempotency Keys

Generate deterministic keys for operations.

Step 3: Configure Bulkheads

Separate queues for different priorities.

Step 4: Set Up Dead Letter Queue

Handle permanent failures gracefully.

Output

• Circuit breaker protecting Vercel calls
• Idempotency preventing duplicates
• Bulkhead isolation implemented
• DLQ for failed operations

Error Handling

Issue	Cause	Solution
Circuit stays open	Threshold too low	Adjust error percentage
Duplicate operations	Missing idempotency	Add idempotency key
Queue full	Rate too high	Increase concurrency
DLQ growing	Persistent failures	Investigate root cause

Examples

Quick Circuit Check

const state = vercelBreaker.stats().state;
console.log('Vercel circuit:', state);

Resources

• Circuit Breaker Pattern
• Opossum Documentation
• Vercel Reliability Guide

Next Steps

For policy enforcement, see vercel-policy-guardrails.