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workers-migration

tessl install https://github.com/secondsky/claude-skills --skill workers-migration

github.com/secondsky/claude-skills

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.

Review Score

92%

Validation Score

13/16

Implementation Score

88%

Activation Score

100%

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

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