Page 5: Advanced Configuration, Domains & Troubleshooting

5. Advanced Configuration, Domains & Troubleshooting

Beyond basic deployment, Vercel offers advanced features and tools for managing your applications effectively.

5.1. Custom Domains and SSL

To use a custom domain (e.g., api.yourdomain.com for your API, yourdomain.com for your frontend), go to your Vercel project settings, then "Domains". Add your domain and follow the instructions to configure your DNS records.

Vercel automatically provisions and renews SSL certificates for your domains, ensuring secure communication (HTTPS) without manual configuration.

5.2. Environment Variables Best Practices

Always use Vercel's environment variables feature for sensitive data (API keys, database credentials) instead of hardcoding them. You can scope them to different environments (Production, Preview, Development).

For example, if your Express.js API needs a database URL:

• Name: DATABASE_URL
• Value: mongodb+srv://...
• Environments: Production, Preview, Development

5.3. Logging and Debugging

Vercel provides a powerful Logs tab in your project dashboard. Here, you can see real-time logs from your Next.js server-side functions and your Express.js serverless functions.

• Check logs for any errors during build or runtime.
• Use console.log() in your serverless functions; these will appear in the Vercel logs.
• For local debugging, ensure your Next.js and Express.js apps run on their respective ports and can communicate.

5.4. Common Troubleshooting Tips

• "404 Not Found" for API: Double-check your vercel.json's rewrites and functions paths. Ensure the Express.js entry point (e.g., api/index.js) is correct.
• CORS Errors: In development, ensure you have the cors middleware enabled in Express.js. In production, Vercel's routing often makes CORS less of an issue if all requests go through the same domain, but if your API is on a subdomain, configure cors properly.
• Build Failures: Check the build logs in Vercel for specific error messages. Often, it's missing dependencies or incorrect build commands (though Vercel is good at auto-detecting for Next.js). Ensure api/package.json has all required dependencies for the Express app.

By following these steps, you can confidently deploy and manage your Next.js and Express.js applications on Vercel.