Cloudflare Error 520
Critical
Web server is returning an unknown error
The origin server returned an empty, unknown, or unexpected response to Cloudflare.
Impact: Website completely inaccessible
Responsibility
Origin Server
This error originates from your origin server. Check origin load and logs.
Common Causes
- Origin server crashed or restarted
- Origin firewall forcibly closed the TCP connection
- Response headers exceeded 8KB
- Origin returned an invalid HTTP status code
Troubleshooting Guide
1
Check Origin Logs
Search Nginx/Apache or application logs on your origin for crashes matching the timestamp of the 520 error.
2
Check Response Header Size
Cloudflare limits response headers to 8KB. Excessive Set-Cookie headers often trigger 520 errors.