← All Status Codes
502
Bad Gateway
🔴 Server Error
Critical Risk
📖 What Is HTTP 502?
The server acting as a gateway or proxy received an invalid response from the upstream server. The backend server is down, overloaded, or returning malformed responses.
🛡️ Security Implications
Repeated 502 errors may indicate a DDoS attack overwhelming the backend. Monitor backend health and implement circuit breakers.
🔍 Common Causes
Backend server crashed, PHP-FPM process died, upstream timeout, firewall blocking backend, DNS resolution failure, or backend overloaded.
🔧 How to Fix
Check backend server status. Restart PHP-FPM/application server. Increase proxy timeout values. Check backend firewall rules. Monitor backend memory and CPU.
🖥️ How to Check
curl -I -o /dev/null -w "%{http_code}" https://example.com