[chef] Actions taken when adding new nodes

[< >]

I see that Chef has a feature where a node recipe can take actions based on
searching, for example, for all existing nodes that have a particular role, 
say
XX. If a node with role XX is then added or removed, the value of the search
will then be different. Is there some mechanism that will cause the code that
did the search to be run again? If so, what is the mechanism and are there any
potential pitfalls when using it?