502 Bad Gateway

A gateway or proxy got an invalid response from the server behind it.

What to do

A proxy or gateway got a bad response, or none, from the server behind it. Check the upstream is running and listening where the proxy expects. The proxy's error log names the reason.

Class
5xx Server Error. The server failed to fulfill a request that looked valid.
Registered
Yes, in the IANA HTTP status code registry.
Cacheable by default
No. A cache stores it only when Cache-Control or Expires says to.
References
RFC 9110 ยง15.6.3 · MDN

Every 5xx code

All HTTP status codes, in one table