Bash Script to disturb services for testing | Which would you say are crucial and/or won't be noticed at first?

I am wondering about a pentesting or better crashtesting script, that randomly kills or disrupts services through deleting a file, blocking access or other example actions that simulate every day outtages in a server/computer pool environment.

I will gladly share the end result, but I am more asking my fellow companions here about ideas what you encountered and had to fix or counteract in your experience.

What services would you consider crucial? Like dhcpd, DNS or the mailserver or one of its configs.

P.S.: I thought about which Reddit this would most belong to, but didn't know if /selfhosted or any other was better suited for this. Thank you.

EDIT: The idea is to build a system that notices such disturbances as corrupted files or failing services and acts on it.