Proxy from another domain to a virtualhost

The first two vhosts works as expected. The second one proxy a Odoo server. I would like to make another proxy from my secondary domain to my Odoo server. However, Odoo must receive the subdomain matching the database, else it won't serve it.

Here's my code for now:

# static homepage

<VirtualHost *:80>
    ServerName mydomain.fr
    ServerAlias www.mydomain.fr
    DocumentRoot /var/www/odoo
</VirtualHost>


# wildcard proxy for odoo:
# one subdomain -> one database

<VirtualHost *:80>
    ServerName mydomain.fr
    ServerAlias *.mydomain.fr

    ErrorLog /var/log/odoo/odoo-error.log
    CustomLog /var/log/odoo/odoo-access.log combined
    LogLevel warn

    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    ProxyRequests Off
    ProxyPass / http://mydomain.fr:8089/
    ProxyPassReverse / http://mydomain.fr:8089/

    ProxyVia On
</VirtualHost>


# a secondary domain
# should point to a specific database

<VirtualHost *:80>
    ServerName www.secondary-domain.com
    ServerAlias secondary-domain.com

    ProxyRequests Off
    ProxyPreserveHost On
    ProxyPass / http://some_database.mydomain.fr
    ProxyPassReverse / http://some_database.mydomain.fr

    ProxyVia On
</VirtualHost>


################
# restrictions #
################

<Location /web/database>
    Order deny,allow
    Deny from all
    Allow from x.x.x.x
</Location>

I'm not really into server management, so I don't know much (even after reading the docs).

Forgot to mention what I get in response:

• secondary-domain.com gives me a 502 Proxy Error
• some_database.mydomain.fr works as expected

If I put the third bloc in second position, the whole site mydomain.fr lags and that does not solve the 502 Proxy Error for my secondary domain.

If I quote the ProxyPreserveHost directive, going to secondary-domain.com leads to secondary-domain.com, some_database.mydomain.fr... What is happening here ?

I need confirmation that this can be done and that my setup is doing that:

1. User asks for secondary-domain.com
2. Third vhost entry proxies the request to some_database.mydomain.fr
3. Second vhost entry proxies the request to mydomain.fr:8069