How to Solve Error 521 Cloudflare?

I keep getting a error 521 on a site I have running the one-click WordPress install on a Ubuntu droplet. I saw on Cloudflare’s website that you need to make sure their IPs are whitelisted which I did through the firewall in networking. The SSL I have activated currently is Full (non strict). I found another thread that suggested running this command: iptables -A INPUT -p tcp -m tcp --dport 443 -j ACCEPT

This did not solve the issue for me. What is odd is that I can refresh the page sometimes and it lets me go to the site, but when I navigate to another page it happens almost every time, but again allows me to go through if I refresh.

Any help would be greatly appreciated!


Not enough info really. You can disable Cloudflare to see if your server resolves or not then narrow down the issue. If you didn’t install SSL on your server yet, might also be the problem.

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Whitelisting all Cloudflare IP v4 and v6 ranges with this script helped to solve the problem in my case:

Spent 3 hours debugging this and finally realized that mod ssl was not enabled on a fresh LAMP Stack. Experienced this on 4 new LAMP servers on Ubuntu 20.04. It seems like it does not come with mod ssl enabled by default. :facepalm

For anyone experiencing this, run the code below in the terminal

a2enmod ssl
service apache2 restart

I wanna move domain from Godaddy to Digital Ocean With database Without any plugin. Is it Possible via FTP or putty?

What are the steps that needed for me. Any one give me a suggestion with complete information.


In order to use the Full SSL option provided by Cloudflare you need to make sure that you have an SSL certificate installed on your Droplet as well.

If this is not the case, what I could suggest is changing the SSL mode from Full to Flexible and then it should fix the problem for you.

Hope that this helps! Regards, Bobby