I will say what worked for me, the others answers above didn't help to my case at all. I hope it can help someone.
Actually, I'm using Virtual host configuration (sites-available / sites-enabled) on EC2 Linux AMI with Apache/2.4.39 (Amazon). So, I have 1 ec2 instance to serve many sites (domains).
Considering that you already have Virtual Host installed and working. In my folder /etc/httpd/sites-available, I have some files with domain names (suffix .conf), for example: domain.com.conf. Create a new file like that.
sudo nano /etc/httpd/sites-available/domain.com.conf
<VirtualHost *:80>
ServerName www.domain.com
ServerAlias domain.com
DocumentRoot /var/www/html/domain
</VirtualHost>
For each file.conf in sites-available, I create a symbolic link:
sudo ln -s /etc/httpd/sites-available/domain.com.conf /etc/httpd/sites-enabled/domain.com.conf
This is the default configuration, so, if access directly by IP of Server, you will be redirect to DocumentRoot of the first file (.conf) in sites-available folder, sorted by filename.
To have a default DocumentRoot folder when access by IP, you have to create a file named 0a.conf, then apache will serve this site because this new file will be the first in sites-available folder.
You must create a symbolic link:
sudo ln -s /etc/httpd/sites-available/0a.conf /etc/httpd/sites-enabled/0a.conf
To check serving order, use it:
sudo apachectl -S
Now, restart apache, and check out it.
Be happy =)