How to secure an Ubuntu 16.04 LTS server

https://www.thefanclub.co.za/how-to/how-secure-ubuntu-1604-lts-server-part-1-basics

The Perfect Server – Ubuntu 16.04 (Xenial Xerus) with Apache, PHP, MySQL, PureFTPD, BIND, Postfix, Dovecot and ISPConfig 3.1

https://www.howtoforge.com/tutorial/perfect-server-ubuntu-16.04-with-apache-php-myqsl-pureftpd-bind-postfix-doveot-and-ispconfig/

How To Protect WordPress with Fail2Ban on Ubuntu 14.04

https://www.digitalocean.com/community/tutorials/how-to-protect-wordpress-with-fail2ban-on-ubuntu-14-04

UFW Essentials: Common Firewall Rules and Commands

https://www.digitalocean.com/community/tutorials/ufw-essentials-common-firewall-rules-and-commands

Other readings…

Potential ufw and fail2ban conflicts

http://askubuntu.com/questions/54771/potential-ufw-and-fail2ban-conflicts