The ispconfig firewall is multiserver capable already.
I have only one question, how ispconfig creates a todo action at another server ? So: i set an action from S1 , but server S2 will execute it?
There are two kind of actions implemented. If a event contains data and is based on a mysql database table, then a table event is used. If a action does not contain any data and is just a notification to do something on a remote server like install system updates, then a action is used. For most situations, you will use a table event. Table events are defined in the module file of the module (in /usr/local/ispconfig/server/mods-enabled) and then you bind a processing function in your plugin to that table event.