How do I troubleshoot a 502 Bad Gateway error?

Check if your backend application process is running, review Nginx/Apache error logs, and verify that the backend is listening on the expected port.

What is the difference between 502 Bad Gateway and 504 Gateway Timeout?

502 means the upstream server replied with an invalid response or reset the connection immediately. 504 means the upstream server failed to respond within the allowed timeout window.

How do I check if my website is serving 502 errors?

Test your URL in our HTTP Header Checker to inspect response status codes in real time.

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HTTP Status Code Reference

HTTP 502: Bad Gateway

Indicates that the server, while acting as a gateway or proxy, received an invalid response from the inbound server.

Status Code

502

Classification

5xx Server Error

Reason Phrase

Bad Gateway

Specification

RFC 9110, Section 15.6.3

Inspect Live HTTP Headers & Status Codes

Test any URL to verify whether it returns HTTP 502 Bad Gateway, measure TTFB latency, and trace redirect chains.

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Common Causes & Triggers

The upstream application process (Node.js/PM2, PHP-FPM) crashed or is not running.
The reverse proxy is configured with an incorrect upstream port or socket path.
A firewall or security group blocks traffic between the reverse proxy and upstream origin.

Troubleshooting & Resolution

Check if your upstream daemon is running (e.g., 'pm2 status' or 'systemctl status php-fpm').
Inspect reverse proxy logs (e.g. 'connect() failed (111: Connection refused)' in Nginx logs).
Verify the internal port and IP in your reverse proxy proxy_pass directive.

Search Engine (Googlebot) SEO Impact

Severe. Extended 502 downtime leads search engines to drop pages from indexation within days.

Inspect via Terminal (cURL)

Execute this command to inspect headers and response codes from your terminal:

curl -i https://example.com

Frequently Asked Questions

Technical answers and debugging guidelines for HTTP 502 Bad Gateway.

HTTP 502 means an edge proxy or web server (like Nginx or Cloudflare) received an invalid response or connection drop from the backend application server.