If your website is experiencing a DDoS attack, then Cloudflare could help to mitigate it.
Cloudflare service has feature that you can use while under a DDoS attack. You can enable it from your cPanel -> Cloudflare icon, then click Manage next to the entry for your domain name. Select the Settings tab and change the Cloudflare Security Settings option to I’m Under Attack.
When this option is enabled, every visitor for your website will see a processing page for a longer time. During that period Cloudflare will verify if the access is legitimate visitor and not from a bot.