HTTP 502 Bad Gateway

In short: A gateway or proxy received an invalid response from the server behind it.

In more detail: Typical with nginx, Cloudflare or load balancers.

In Depth

Possible causes

• Backend process crashed or restarted.
• Wrong upstream port.
• Timeout at the backend.

Solutions

1. Check and restart the backend service.
2. Check proxy configuration and ports.
3. Compare logs of proxy and application.

See also: HTTP 500 Internal Server Error, HTTP 504 Gateway Timeout, Load Balancing