I can't agree with this. In the case that was debugged, the configuration change was probably legitimately changed for a valid business reason and was codified.

I can't agree with this. In the case that was debugged, the configuration change was probably legitimately changed for a valid business reason and was codified. If you have traditional VM infrastructure your provisioning may consist of 100s of small configuration changes. Are you really going to step through every single one of them manually? Configuration management tools don't exactly have a `git bisect` equivalent, and even if you did, you'd have to re-image the VM every time because VMs are stateful. And even if you could somehow bisect every single configuration change in your configuration management, there's the added complexity of how many configuration changes are actually needed to test if the problem is still present. In this case it would probably be fairly easy because DNS is such a core "feature", but if this is something more application-level, you're really going to be lost.