Error 521: web server is down
Error 521 occurs when the origin web server refuses connections from Cloudflare. Security solutions at your origin may block legitimate connections from certain Cloudflare IP addressesOpen external link.
The two most common causes of 521 errors are:
- Offlined origin web server application
- Blocked Cloudflare requests
Resolution
Contact your site administrator or hosting provider to eliminate these common causes:
- Ensure your origin web server is responsive
- Review origin web server error logs to identify web server application crashes or outages.
- Confirm Cloudflare IP addressesOpen external link are not blocked or rate limited
- Allow all Cloudflare IP rangesOpen external link in your origin web server’s firewall or other security software
- Confirm that — if you have your SSL/TLS mode set to Full or Full (Strict) — you have installed a Cloudflare Origin Certificate
- Find additional troubleshooting information on the Cloudflare CommunityOpen external link.
You can read more at Troubleshooting Cloudflare 5XX errors · Cloudflare Support docs.