You can use Apache’s Alias directive to point a path to a specific directory outside of your web root. For example, let’s say your storage volume is mounted at /mnt/volume-nyc1-01 and that you want http://example.com/images to be served from the volume. First, you would need to create a directory on the volume that you can give ownership to the www-data user. E.g:

mkdir /mnt/volume-nyc1-01/images
sudo chown -R www-data:www-data /mnt/volume-nyc1-01/images

Then you’ll need to edit your Apache configuration. By default, that is found at /etc/apache2/sites-enabled/000-default.conf. Now add an Alias directive pointing /images to /mnt/volume-nyc1-01/images:

        Alias /images /mnt/volume-nyc1-01/images
        <Directory /mnt/volume-nyc1-01/images>
                Require all granted
        </Directory>

Finally, restart Apache for the changes to take effect:

sudo service apache2 restart

You can find out more details about how Block Storage volumes work in this tutorial: https://www.digitalocean.com/community/tutorials/how-to-use-block-storage-on-digitalocean