You should set up vHosts on Apache (see documentation below). Once you have done that, you will need to point your A record towards your Azure Public IP address.
Once this has been completed, you should now be able to go to your Domain (www.domain.com) and it will know how to route to your /var/www/ directory.
https://www.digitalocean.com/community/tutorials/how-to-set-up-apache-virtual-hosts-on-ubuntu-16-04