Amazon Cloud : AWS Linux Server Tips, Tricks & Tutorials

Symptoms When visiting the website, it fails to load with error 521. The error occurs because the origin web server refused the connection from CloudFlare CloudFlare is used Website uses Nginx as a reverse-proxy; Cause CloudFlare IP addresses were blocked by  nginx  because of outdated contents of  /etc/nginx/conf.d/cloudflare.conf . /etc/nginx/conf.d/cloudflare.conf  contains old CloudFlare IP addresses list. Solution Make sure that you're not blocking CloudFlare IPs in  .htaccess ,  iptables , or your firewall. 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 connect...