Summary 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.
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 definedLambda/Express File system access Use KV/R2 for storage Buffer is not definedNode.js Node.js globals Import from node:buffer process.env undefinedAll Env access pattern Use env parameter setTimeout not returningLambda Async patterns Use ctx.waitUntil() require() not foundExpress CommonJS Convert to ESM imports Exceeded CPU timeAll Long computation Chunk or use DO body already consumedExpress Request body Clone before read Headers not iterableLambda Headers API Use Headers constructor crypto.randomBytesNode.js Node crypto Use crypto.getRandomValues Cannot find moduleAll 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_decoderassert Not Supported (need alternatives):
fs → Use R2/KVchild_process → Not possiblecluster → Not applicabledgram → Not supportednet → Use fetch/WebSockettls → Handled by platform
When to Load References Reference Load When references/lambda-migration.mdMigrating AWS Lambda functions references/vercel-migration.mdMigrating from Vercel/Next.js references/express-migration.mdMigrating Express/Node.js apps references/node-compatibility.mdNode.js API compatibility issues
Migration Checklist
Analyze Dependencies : Check for unsupported Node.js APIsConvert to ESM : Replace require() with importUpdate Env Access : Use env parameter instead of process.envReplace File System : Use R2/KV for storageHandle Async : Use ctx.waitUntil() for background tasksTest Locally : Verify with wrangler devPerformance Test : Ensure CPU limits aren't exceeded
See Also
workers-runtime-apis - Available APIs in Workersworkers-performance - Optimization techniquescloudflare-worker-base - Basic Workers setup 