Users are a great example of a resource that may need to be realized by multiple classes. Consider the following situation. To simplify the administration of a large number of machines, you defined classes for two kinds of user: developers and sysadmins. All machines need to include sysadmins, but only some machines need access to developers:
node 'server' {
include user::sysadmins
}
node 'webserver' {
include user::sysadmins
include user::developers
}
However, some users may be members of both groups. If each group simply declares its members as regular user resources, this will lead to a conflict when a node includes both developers and sysadmins, as in the webserver example.
To avoid this conflict, a common pattern is to make all users virtual resources, defined in a single user::virtual class that every machine...
