/cloudflare-workers-migration

name: cloudflare-workers-migration
description: Migrate to Cloudflare Workers from AWS Lambda, Vercel, Express, and Node.js. Use when porting existing applications to the edge, adapting serverless functions, or resolving Node.js API compatibility issues.
metadata:
  version: "1.0.0"
license: MIT

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 crypto | Use `crypto.getRandomValues` | | `Cannot find module` | All | Missing polyfill | Check Workers compatibility |

Quick Migration Patterns

AWS Lambda Handler

// Before: AWS Lambda
export const handler = async (event, context) => {
  const body = JSON.parse(event.body);
  return {
    statusCode: 200,
    body: JSON.stringify({ message: 'Hello' }),
  };
};

// After: Cloudflare Workers
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const body = await request.json();
    return Response.json({ message: 'Hello' });
  },
};

Express Middleware

// Before: Express
app.use((req, res, next) => {
  if (!req.headers.authorization) {
    return res.status(401).json({ error: 'Unauthorized' });
  }
  next();
});

// After: Hono Middleware
app.use('*', async (c, next) => {
  if (!c.req.header('Authorization')) {
    return c.json({ error: 'Unauthorized' }, 401);
  }
  await next();
});

Environment Variables

// Before: Node.js
const apiKey = process.env.API_KEY;

// After: Workers
export default {
  async fetch(request: Request, env: Env): Promise<Response> {
    const apiKey = env.API_KEY;
    // ...
  },
};

Node.js Compatibility

Workers support many Node.js APIs via compatibility flags:

// wrangler.jsonc
{
  "compatibility_flags": ["nodejs_compat_v2"],
  "compatibility_date": "2024-12-01"
}

**Supported with nodejs_compat_v2:**

• `crypto` (most methods)
• `buffer` (Buffer class)
• `util` (promisify, types)
• `stream` (Readable, Writable)
• `events` (EventEmitter)
• `path` (all methods)
• `string_decoder`
• `assert`

**Not Supported (need alternatives):**

• `fs` → Use R2/KV
• `child_process` → Not possible
• `cluster` → Not applicable
• `dgram` → Not supported
• `net` → Use fetch/WebSocket
• `tls` → Handled by platform

When to Load References

| Reference | Load When | |-----------|-----------| | `references/lambda-migration.md` | Migrating AWS Lambda functions | | `references/vercel-migration.md` | Migrating from Vercel/Next.js | | `references/express-migration.md` | Migrating Express/Node.js apps | | `references/node-compatibility.md` | Node.js API compatibility issues |

Migration Checklist

1. **Analyze Dependencies**: Check for unsupported Node.js APIs 2. **Convert to ESM**: Replace require() with import 3. **Update Env Access**: Use env parameter instead of process.env 4. **Replace File System**: Use R2/KV for storage 5. **Handle Async**: Use ctx.waitUntil() for background tasks 6. **Test Locally**: Verify with wrangler dev 7. **Performance Test**: Ensure CPU limits aren't exceeded

See Also

• `workers-runtime-apis` - Available APIs in Workers
• `workers-performance` - Optimization techniques
• `cloudflare-worker-base` - Basic Workers setup