WP-CLI is a set of command-line tools for managing WordPress installations. You can update plugins, set up multisite installs and much more, without using a web browser.
The SPDY protocol has been created by Google to load HTTPS pages faster and improving web security.
It will work only when you have running site with SSL.
The objective of this tutorial is to enable outgoing IP rotation. One of the common use cases of IP rotation is setting up mass mailing server. I am assuming we have already setup the SMTP (MTA) server here listening on all interfaces.
To prevent the server from bruteforce attacks. Fail2ban will monitor the service and block the persons try to harm our server.
SYN Flooding is the most common DDOS attack. I have tried to explain some tweaks through which you can avoid these attacks.