Error 521: Web server is down

Created:

2016-11-16 13:06:01 UTC

Modified:

2017-04-29 09:16:11 UTC

18

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Error 521: Web server is down

Applicable to:

  • Plesk 12.5 for Linux
  • Plesk Onyx for Linux
  • Plesk 12.0 for Linux

Symptoms

  • When you visit a website using CloudFlare, you may receive an error 521. This error occurs because the origin web server refused the connection from CloudFlare.

  • You are using nginx in front of Apache

Error 521

Cause

CloudFlare IP addresses were blocked by nginx because of an outdated contents of /etc/nginx/conf.d/cloudflare.conf .

/etc/nginx/conf.d/cloudflare.conf contains CloudFlare servers IP addresses list.

Resolution

  • Make sure that you're not blocking CloudFlare IPs in .htaccess , iptables , or your firewall.
  • Make sure that /etc/nginx/conf.d/cloudflare.conf is up to date and contains all IP addresses found here: https://www.cloudflare.com/ips
  • Make sure your provider isn't rate limiting or blocking IP requests from the CloudFlare IPs and ask them to whitelist the IP addresses found here: https://www.cloudflare.com/ips
  • Make sure that you're operating off of the most recent versions of Bad Behavior or mod_security . You want to ensure that mod_security's core rules aren't blocking CloudFlare requests.
  • If you are running custom Apache modules, such as mod_antiloris and mod_reqtimeout , disable and unload the modules. These modules will block any time an IP that connects more than 22 times. Since all connections are now coming from a CloudFlare IP, you will definitely hit the limit causing the error page. As soon as you unload the module, the issue will disappear.
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