For true zero-config deployment, ensure your Express app listens on the port provided by the platform's environment variable:

const port = process.env.PORT || 3000;

This single line makes your app compatible with all platforms in this comparison.

Ensure your package.json includes a proper start script:

"scripts": {
  "start": "node server.js"
}

Most platforms detect this automatically. For development, add a separate dev script with nodemon.

Keep sensitive information in environment variables, not in your code:

• API keys and secrets
• Database connection strings
• Authentication credentials

All platforms provide easy ways to set environment variables in their dashboard.

For production apps that need persistent storage:

• Use external database services (MongoDB Atlas, Supabase)
• Store files on S3 or similar services
• Avoid writing to the local filesystem (except in /tmp)

This ensures your data survives deployments and container restarts.