ANSWER:

A role on chef server and chef-solo are very different in how they are represented. In chef-server they’re stored in a database, whereas chef-solo uses flat JSON or Ruby files.

You’d have to ask opscode why it doesn’t work for the chef-solo use case, but my guess is that its just much more involved to create and upload the roles to the database so they aimed to simplify that use case.

Either way, creating roles is pretty simple in Chef-Solo. Just create the directory and the file for the role.

http://wiki.opscode.com/display/chef/Chef+Solo#ChefSolo-Roles

by Kyle from http://serverfault.com/questions/382667