HTTP 502 Bad Gateway — Meaning, Causes & How to Fix

Code

502

Name

Bad Gateway

Class

5xx Server Error

Specification

RFC 9110 §15.6.3

Cacheable by default

Only with explicit Cache-Control / Expires

What HTTP 502 means

502 Bad Gateway is returned by a proxy, load balancer or CDN when the server behind it (the upstream) sent an invalid response — or, very often, refused or dropped the connection. The proxy itself is fine; the app behind it is not.

Common causes

• The application server (PHP-FPM, Node, Gunicorn) crashed or is not running.
• The upstream closed the connection or returned malformed headers.
• Wrong upstream address or port in the proxy config.
• A CDN like Cloudflare cannot reach the origin.

How to fix it

For site owners

• Check that the upstream service is running and listening on the configured port/socket.
• Read the proxy error log (e.g. nginx “upstream prematurely closed connection”).
• Increase upstream buffer sizes if headers are large.

For visitors & developers

• Reload after a moment; 502s are often brief during restarts or deploys.

SEO impact

Like all 5xx errors, frequent 502s make Googlebot crawl less, and URLs that keep failing can be dropped. Brief 502s during a deploy are not a problem.

Example 502 response

HTTP/1.1 502 Bad Gateway
Server: nginx
Content-Type: text/html

Related status codes

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