Apache Web Server is a software package that turns a computer into an HTTP server.
That is, it sends web pages – stored as HTML files – to people on the internet who request them. It is open-source software, which means it can be used and modified freely.

Installation

Refresh your local software package database to make sure you are accessing the latest versions

sudo apt-get update

Install Apache 2

sudo apt-get install apache2

Configure Your Firewall

sudo ufw app list

Output:

Available applications:
  Apache
  Apache Full
  Apache Secure
  OpenSSH

Allow normal web traffic on port 80

sudo ufw allow 'Apache'

Verify the changes by checking UFW status

sudo ufw status

Apache Service Controls

This operation uses the systemctl command, with a series of switches:

Stop Apache:

sudo systemctl stop apache2.service

Start Apache:

sudo systemctl start apache2.service

Restart Apache:

sudo systemctl restart apache2.service

Reload Apache:

sudo systemctl reload apache2.service

Apache Configuration Files and Directories

Directories
After installing, Apache by default creates a document root directory at /var/www/html.

Configuration Files
Apache creates log files for any errors it generates in the file /var/log/apache2/error.log.
It also creates access logs for its interactions with clients in the file /var/log/apache2/access.log.

Like many Linux-based applications, Apache functions through the use of configuration files.
They are all located in the /etc/apache2/ directory.

/etc/apache2/apache2.conf – This is the main Apache configuration file and controls everything Apache does on your system.
Changes here affect all the websites hosted on this machine.

/etc/apache2/ports.conf – The port configuration file.
You can customize the ports Apache monitors using this file.
By default, Port 80 is configured for http traffic.

/etc/apache2/sites-available – Storage for Apache virtual host files.
A virtual host is a record of one of the websites hosted on the server.

/etc/apache2/sites-enabled – This directory holds websites that are ready to serve clients.
The a2ensite command is used on a virtual host file in the sites-available directory to add sites to this location.