From my current understanding of Hawkular, different user IDs do not matter as alerts generate on the base of tenants to which the trigger is associated and tenants are shared between the users.

So we will need only one unique ID per server. There can be 2 ways for it :-
  1. If we don't care for privacy then we can use the location (host+port) as server ID as it will be unique for each server anyway. Plus no need to pass that data to the client as it already knows this.
  2. We can generate one ID per server instance. But then we will need the client to know this value from somewhere.
So only thing client need is to subscribe to server ID and all the tenants from which we wish to receive alerts from.

Aerogear action plugin will send FCM with "AND" topic condition of tenant ID and server ID