Cloud Infrastructure & Web ServersCritical Severity
502 Bad Gateway Error: Nginx, Cloudflare & Node.js Crash Resolution
Applies to: Nginx, Cloudflare, AWS, Node.js
Safety & Usage Advisory
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Estimated Repair Cost
$0
$0 (DevOps / Server Fix)
Diagnostic Category
Cloud Infrastructure & Web Servers
Nginx, Cloudflare, AWS, Node.js
Fix Difficulty
Beginner
~30-60 Mins Required
Common Symptoms
- Browser displays '502 Bad Gateway'
- Cloudflare Error 502 Host Error screen
- Nginx gateway timeout / connection refused
Root Causes
- Node.js / Python upstream server process crashed (OOM / unhandled error)
- Nginx proxy_pass port mismatch (e.g. listening on 3000 vs 8080)
- PHP-FPM pool crashed under heavy traffic load
- Firewall blocking internal reverse proxy connections
Step-by-Step Instructions to Fix HTTP 502
1
Check Backend App Process Status
Run `pm2 status` or `systemctl status your-app` to verify your backend process is running.
2
Inspect Nginx Error Logs
Run `tail -n 100 /var/log/nginx/error.log` to view exact connection refused details.
3
Restart Upstream Service and Reload Nginx
Restart your app daemon and run `sudo systemctl reload nginx`.
How to Prevent HTTP 502 in the Future
- Set up automated process managers like PM2 or Kubernetes self-healing pods with health check endpoints
HTTP 502 Troubleshooting FAQs
A 502 occurs when an edge proxy (like Nginx or Cloudflare) attempts to connect to an origin application server, but the origin server is either down or sends an invalid response.