Fail2ban is a linux software which tracks login attempts through the client's ip. After certain failed login attempts the ip address of the client will be blocked to ensure that no brute force attack is happening.
This is a fail2ban filter for openVPN service on Linux. This filter was tested on Debian 8 and Ubuntu 16.04.
This is tutorial shows how to add a Fail2ban custom filter rule for web applications e.g. joomla admin page, moodle, wordpress.
Fail2ban is needed to block brute-force attacks. Easiest explanation: this attack is performed when page is entered through trying passwords again and again till the right password was found. This will be avoided for your web application by this fail2ban custom filter rule.