So one of the most hardest things to back up regularly is going to be here active directory.
Due to the complex and constantly changing environment this otherwise great piece of software is set in makes it very difficult have a backup of.
Without going into too much detail: in one of the more recent rent somewhere attacks one of the largest shipping companies in the world was it by that aforementioned piece of friends number to a degree where they became an operational. In fact, they were crippled in their operations so hard that orders from customers have to be taken through private cell phone/WhatsApp accounts of employees.
The reason this incident was so messy was the fact that all of their domain controllers which replicate automatically between different offices day had across the globe and therefore the rent somewhere made it to pretty much every domain controller.
Well, they got lucky because in one of their African subsidiaries the office they maintain their suffered a power outage on that day.
This led to the fact that they had one existing copy of their Domain controller available.
So while it may seem a funny, and almost stupid solution the only way to maintain a quality of data, and a certain resilient action plan against domain controllers feeling an organization by shutting down one domain controller every day for 24 hours.
In case of a cyber attack taking place this single domain controller can then be replicated to the rest of the organization once infected systems have been restored.
https://lars-hilse.de/lhx18/2019/10/what-active-directory-backup-do-you-pursue/