CompositeController shouldn't allow empty parent selector. about metacontroller

[groner]

In my initial evaluation of metacontroller, I created a composite controller with a v1/configmaps child resource and no selector. This resulted in the compositecontroller deleting all the configmaps in that namespace.

This wasn't a big problem in my development environment, but it could be an unpleasant surprise for someone if they decided to test this in a less isolated environment.

[enisoc]

Hm that's a good point. I've also had a similar concern with PVCs. It's unfortunate that StatefulSet does not claim the PVCs it creates in any way, so they appear as orphans. If the label selector matches, another controller like CatSet might adopt and delete the PVCs (because they aren't part of the desired state).

Maybe in addition to bailing out if the selector is empty, we should consider limiting the adoption logic to more confined scenarios. It seems rare that people writing custom controllers really want to take ownership of existing objects.

For now, I'll prioritize adding the check for an empty selector since the case you pointed out is a potentially nasty one. Thanks for reporting!