Is it possible to define nodegroups outside of the master config file (/etc/salt/master). It seems that something as dynamic node groups shouldn't be in the master config, or am I thinking about nodegroups the wrong way.
Here's my scenario, our servers are classified by role in their naming convention. Which means we have multiple servers named location-nginxXX.mydomain.com, where the XX denotes the node. The applications on the node can/will change over time. As we move an application from one node to another we want to target the new node with additional states and pillar items. Ideally, we'd update some config (pillar, maybe?) with the list of servers assigned to a given application. Then we update the servers with the states for the new application, and remove the states no longer needed.
Is our approach sound, and if so, how do you target a changing set of minions with states and pillars?
If you're using nodegroups 'dynamically' then this is usually done using one of the compound matchers. you define a nodegroup (in master) that matches something that can be changed elsewhere in the config (grains being the most common, but pillars also works). When you want to change a server's group, just modify it's config to be matched by a different nodegroup.