Only one key comes with Unity 3.1 and below. Unity 4.0 uses a different licensing mechanism, but it is still bound to exactly one server. The purpose is to enforce that you buy a Unity license for every server you run it on.
For lab purposes, Unity will run without a license in "demo" mode, where you may have only a very limited number of users, and only 15 second messages, but almost all the "bells and whistles" features are enabled for you to play around with.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.