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

Top 10 Migration Errors

fs is not defined

Buffer is not defined

node:buffer

process.env undefined

env

setTimeout not returning

ctx.waitUntil()

require() not found

Exceeded CPU time

body already consumed

Headers not iterable

crypto.randomBytes

crypto.getRandomValues

Cannot find module

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

references/lambda-migration.md

references/vercel-migration.md

references/express-migration.md

references/node-compatibility.md

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