In Hawkular Alerts we have an email plugin that adds support to explicit recipients.
We may need a new plugin for "internal" users/roles that are defined inside hawkular.
In this case, we should know only the username/groupname and we may need a service to resolve or just to send the message.
Hawkular may have some "preferences" for user/group, using different transports, i.e. if day hours use email, but in night hours use the phone.
From the alerts action perspective we will have some definition as send to "user:john or group:administrators" where "john"/"administrators" are the username/groupname.
One of the doubts on the implementation side is if we need a "resolution service" like "user:john" will be "email:email@example.com" or "sms:+12345678" depending of some preferences condition. Or if we need an additional service.
As we have plugins for email and other transports, a resolution service may have sense to reuse this plugins, on this case, this new plugin may reuse others once the resolution is done, instead to repeat code for sending email or other transports.