Cloudflare Error 521
Critical
Web server is down
Cloudflare can resolve your origin IP, but the origin server refused the connection (e.g., service stopped or port closed).
Impact: Website completely inaccessible
Responsibility
Origin Server
This error originates from your origin server. Check origin load and logs.
Common Causes
- Origin web service process (e.g., Nginx) is stopped
- Origin server is entirely offline
- Origin firewall blocks the port (80/443)
Troubleshooting Guide
1
Verify Service Status
Log into the origin and run `systemctl status nginx` or `netstat -tlnp` to ensure port 80/443 is listening.
2
Check Security Groups & Firewalls
Ensure the origin cloud provider (e.g., AWS Security Group) allows ingress to 80/443 from all IPs, or at least Cloudflare IPs.