I have an app with setup.xml where a hostname is entered. I've also made a custom conf file and setup the REST endpoint for it. A python script uses this info. This all works great.
However, I need workflow_actions.conf to also know about that hostname in the URL of an action (link.uri).
What's the best way to go about this in splunk?
There is no way to get a configuration file to reference another configuration file, at least not in the way you describe.
However, Splunk has a way to store "state information" like a hostname. There are two variations.
First, you could write the information to a csv file stored in the lookups subdirectory, and set up the csv file as a lookup.
Or, you could write the information (as a collection) to the KV store and set up a lookup based on the collection.
Here is some documentation that may help:
Tutorial: Use KV Store with a simple app