Some time ago a company named codespaces had a problem. An evil person had gained access to their cloud and deleted so much data that their core-business was basically erased from existance.
So why do I call this unnecessary and naive? Because what happened to them is textbook stuff and indeed you 'll find this in any book about security. Even "The Daily Worse Than Failure" has stories like this every week.
1. Never put business critical data on servers you do not fully control.
There is a reason why firewalls use IP-based security. Only a handfull of people at codespaces needed to be able to login, the rest of the world should not even have been able to ping the server, let alone get to the login page.
Controlling your own servers also means that you have the ability to physically disconnect them from the internet. When stuff begins to disappear, you unplug, stopping the hacker dead in his tracks. Downtime is a nuissance, losing data can, well, cost you your business.
2. Never use the same credentials for multiple servers.
Credentials get compromised, that's just how it is, and that's why you want to limit the amount of access each of the sers of credentials grant. Putting everything behind the same set is just plain stupid. Sorry, there is no other word for it.
3. Always keep your backups separate from the server.
Backups are meant to help you recover from disasters like, say, a hacker stealing your admin credentials and erasing your data. In the 'good old days' people put data on tapes and physically took those tapes to a safe, and a copy to a safe in another building. Why? In case of a burglary, or a fire, or... heck, whatever happened that caused the data to get destroyed. Today apparently it is perfectly acceptable to just have a file "in the cloud" and stick it behind the same password that can erase the original data...
4. Standby-servers are not a luxury.
When the hacker started to shut down servers, backupservers should have kicked in to continue the service. Having different passwords and separate backups, the customer would probably not even have noticed that there was ever any problem.
For those of you who think "well, hind-sight is always 20/20".... no. These points are common knowledge that any syadmin should know by heart. CodeSpaces fell for the cloud hype and it cost them theyr company. It's sad but any sysadmin would have told them this was a very bad setup.