502 Bad Gateway
5xx Server Error

The 502 (Bad Gateway) status code indicates that the server, while acting as a gateway or proxy, received an invalid response from an inbound server it accessed while attempting to fulfill the request.

RFC 7231 6.6.3


This status code is often encountered when a reverse proxy can’t find a downstream server to serve the request (often because it exploded, or there’s not enough of them to serve the traffic).