Running multiple Instances of the application.

[titusz]

Currently a user can start multiple instances of the application. The behavior of this, depending on node management setting is "undefined". We should decide if we allow multiple instances at all. If we do allow them, we should describe for what cases this would be usefull and define the required conditions needed to run multiple instances without problems (no two managed nodes on the same port are possible). If we do not allow it we should find a way to prevent the launch of multiple instances or at least issue a warning if a second instance is launched.