Error 520 occurs when the origin server returns an empty, unknown, or unexpected response to Cloudflare.
Contact your hosting provider or site administrator and request a review of your origin web server error logs for crashes and to check for these common causes:
- Origin web server application crashes
- Cloudflare IPs not allowed at your origin
- Headers exceeding 16 KB (typically due to too many cookies)
- An empty response from the origin web server that lacks an HTTP status code or response body
- Missing response headers or origin web server not returning proper HTTP error responses
520 errors are prevalent with certain PHP applications that crash the origin web server.
If 520 errors continue after contacting your hosting provider or site administrator, provide the following information to Cloudflare Support:
- Full URL(s) of the resource requested when the error occurred
- Cloudflare cf-ray from the 520 error message
- Output from http://www.example.com/cdn-cgi/trace (replace www.example.com with your hostname and domain where the 520 error occurred)
- Two HAR files:
- one with Cloudflare enabled on your website, and
- the other with Cloudflare temporarily disabled.