Using different sessions per vhost - http://stackoverflow.com/questions/18262878/how-to-prevent-php-sessions-being-shared-between-different-apache-vhosts

httpd.conf

<VirtualHost *:81>
    DocumentRoot /var/www/xxx1
    <Directory "/var/www/xxx1">
        AllowOverride All
        php_value session.save_path "/var/mysessionforproject_1"
   </Directory>
</VirtualHost>

<VirtualHost *:82>
    DocumentRoot /var/www/xxx2
    <Directory "/var/www/xxx2">
        AllowOverride All
        php_value session.save_path "/var/mysessionforproject_2"
   </Directory>
</VirtualHost>