When working on T282806 it surfaced the need to be able to select which Prometheus instance to install files to. Specifically around the global instance which behaves slightly different than other instances by virtue of aggregating data, therefore:
- The default is to deploy alerts only to site-local Prometheus instances (i.e. all but global)
- For use cases where global visibility is needed then users can override the default by marking alerting rule files to be installed in the global instance (exact mechanism TBD)
Sort of unrelated to the task at hand but if/when in the future we're deprecating the global instance in favor of letting Thanos evaluate global alerts we can reuse the same mechanism to install rules into Thanos instead.