504 Gateway Timeout

Server error: the request may be fine, but the server failed to carry it out.

When a server should send it. By a gateway or proxy when the server behind it did not answer in time. nginx's proxy_read_timeout and fastcgi_read_timeout default to 60 seconds.

Common causes. Slow database queries, long running scripts or an overloaded backend.

What to do. Retry. Site owners should find the slow request; raising the proxy timeout only hides it.

Browsers and HTTP clients. Browsers show the proxy's error page. The request may still be running on the backend, so a retried POST can run twice.

Google Search. Googlebot treats 5xx responses as a sign of trouble and temporarily slows its crawl rate. Already indexed URLs are kept at first, but are dropped if the errors continue. Source: Google Search Central, How HTTP status codes, and network and DNS errors affect Google Search.

Caching. Not cacheable by default (RFC 9110 section 15.1 does not list it). A cache stores it only when the response says so with Cache-Control or Expires.

HTTP/1.1 504 Gateway Timeout
Content-Type: text/plain; charset=utf-8

Gateway Timeout

location /example {
    return 504;
}

RewriteEngine On
RewriteRule ^example$ - [R=504,L]

http_response_code(504);
echo 'Gateway Timeout';
exit;

res.writeHead(504, { 'Content-Type': 'text/plain' });
res.end('Gateway Timeout');

# in a view function
return 'Gateway Timeout', 504