virtualhost – Apache add new site as subdomain on server

I have two sites which runs independently on my VPS, let’s call them site1 and site2.

They are respectively located at /var/www/html/site1 and /var/www/html/site2

I don’t have a domain name yet but I can acces my site using server IP, let’s say its adress is 8.8.8.8

I currently have two separate apache configuration file for each site.

Both sites are configured as follow, only DocumentRoot and the second Directory block differs.

<VirtualHost *:80>
    ServerName 8.8.8.8
    DocumentRoot /var/www/html/site
    <Directory />
        Options FollowSymLinks
        AllowOverride All
    </Directory>
    <Directory /var/www/html/site>
        AllowOverride All
    </Directory>

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

I can acces both my site by enabling one and disabling the other one.

What I would like to do is to have site1 on http://8.8.8.8 and test site on http://site2.8.8.8.8

I tried the following configuration without success

<VirtualHost *:80>
    ServerName 8.8.8.8
    DocumentRoot /var/www/html/site1
    <Directory />
        Options FollowSymLinks
        AllowOverride All
    </Directory>
    <Directory /var/www/html/site1>
        AllowOverride All
    </Directory>

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

<VirtualHost *:80>
    ServerName site2.8.8.8.8
    DocumentRoot /var/www/html/site2
    <Directory />
        Options FollowSymLinks
        AllowOverride All
    </Directory>
    <Directory /var/www/html/site2>
        AllowOverride All
    </Directory>

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

Do I need DNS records to be able to achieve my goal ?

I not, how should I configure apache and my VPS to be correctly redirected with either sit1 or site2 depending on the IP prefix ?