workers-migration

# Workers Migration Guide

Migrate existing applications to Cloudflare Workers from various platforms.

## Migration Decision Tree

```
What are you migrating from?
├── AWS Lambda
│   └── Node.js handler? → Lambda adapter pattern
│   └── Python? → Consider Python Workers
│   └── Container/custom runtime? → May need rewrite
├── Vercel/Next.js
│   └── API routes? → Minimal changes with adapter
│   └── Full Next.js app? → Use OpenNext adapter
│   └── Middleware? → Direct Workers equivalent
├── Express/Node.js
│   └── Simple API? → Hono (similar API)
│   └── Complex middleware? → Gradual migration
│   └── Heavy node: usage? → Compatibility layer
└── Other Edge (Deno Deploy, Fastly)
    └── Standard Web APIs? → Minimal changes
    └── Platform-specific? → Targeted rewrites
```

## Platform Comparison

| Feature | Workers | Lambda | Vercel | Express |
|---------|---------|--------|--------|---------|
| **Cold Start** | ~0ms | 100-500ms | 10-100ms | N/A |
| **CPU Limit** | 50ms/10ms | 15 min | 10s | None |
| **Memory** | 128MB | 10GB | 1GB | System |
| **Max Response** | 6MB (stream unlimited) | 6MB | 4.5MB | None |
| **Global Edge** | 300+ PoPs | Regional | ~20 PoPs | Manual |
| **Node.js APIs** | Partial | Full | Full | Full |

## Top 10 Migration Errors

| Error | From | Cause | Solution |
|-------|------|-------|----------|
| `fs is not defined` | Lambda/Express | File system access | Use KV/R2 for storage |
| `Buffer is not defined` | Node.js | Node.js globals | Import from `node:buffer` |
| `process.env undefined` | All | Env access pattern | Use `env` parameter |
| `setTimeout not returning` | Lambda | Async patterns | Use `ctx.waitUntil()` |
| `require() not found` | Express | CommonJS | Convert to ESM imports |
| `Exceeded CPU time` | All | Long computation | Chunk or use DO |
| `body already consumed` | Express | Request body | Clone before read |
| `Headers not iterable` | Lambda | Headers API | Use Headers constructor |
| `crypto.randomBytes` | Node.js | Node c