Role dependencies

Hello,

I have a playbook with one role to install an application split on 2 servers, so the inventory file contains 2 entries like this:

[DV70_DEV]
ansible_host=server1 ansible_user=usertest PARAM=WEB
ansible_host=server2 ansible_user=usertest PARAM=DATABASE

I want once the both installation are done, a dependencie to run a rôle Karaf that needs to know the variables:

dependencies:
    - { role: apache, webserver: server1 , dbserver: server2, user: usertest}
How can I manage the dependency to be done once the 2 installations are done , how to manage a boolean ?
How can I manage to know variables from the 2 lines of the inventory file ?

Regards