HTTP 502 Bad Gateway

What it means

502 Bad Gateway means a server acting as a gateway or proxy (nginx, a CDN such as Cloudflare, a load balancer) got an invalid response, or no response, from the upstream server behind it. The front end is up; the application behind it is failing.

Applies to: All browsers, nginx, Apache, Cloudflare, AWS ALB

How to fix HTTP 502 Bad Gateway

1. Reload after a minute; many 502s come from a backend restart or deployment
2. Try another network or device to rule out a broken proxy on your side
3. Clear cache and cookies for the site
4. If you own the site: check that the upstream service is running ('systemctl status php8.2-fpm', 'pm2 status', 'docker ps')
5. If you own the site: read nginx error.log for 'connect() failed', 'upstream prematurely closed' or socket permission errors and fix the upstream address or socket
6. If you own the site: check for out-of-memory kills with 'dmesg | grep -i kill' and raise worker limits or memory as needed
7. If you own the site behind Cloudflare: make sure the origin accepts Cloudflare's IP ranges and responds on the expected port and protocol

Why it happens

The proxy could not get a valid HTTP response from the upstream: the backend process is down or crashed, the socket path or port is wrong, the backend closes connections early, or a firewall blocks proxy-to-origin traffic.

FAQ

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