Causes
- Origin server returns an empty, unknown, or unexpected response to Cloudflare
Fixes
Step 1: Grey Cloud The DNS Record
The quick step is to either grey cloud the DNS record in the Cloudflare DNS app or temporarily pause Cloudflare
Step 2: Contact NET Support
Contact NET support or your 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 whitelisted at your origin web server.
- Origin web server TCP idle timeouts shorter than 300 seconds
- Headers exceeding 8 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
Step 3: Contact Cloudflare Customer Support
If the error continues after contacting NET support or site administrator, provide the following information to Cloudflare Customer Support: –
- Full URL(s) of the resource requested when the error occurred
- Cloudflare cf-request-id or 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 one with Cloudflare temporarily disabled.