Fix Nginx 502 Bad Gateway

I'm experiencing a 502 Bad Gateway error on my Nginx server. Nginx is proxying to a Node.js backend, and the issue is caused by backend server problems.

Ideal Skills and Experience:
- Expertise in Nginx configuration and troubleshooting
- Strong knowledge of Node.js and its server management
- Experience with backend server issue diagnosis and resolution
- Familiarity with log analysis to pinpoint errors