Clearly in the example above, you can afford to hire two sys admins to manage the bare metal servers (you can probably afford more, but 2 is the minimum that gives some peace of mind)
We had an application that was a glorified quiz engine and our customers would mass enrol and mass take the quizzes so the scaling that was offered by Azure made it a no brainer for us, specially as given the nature of our customers, quizzes would only take place during working hours, so we'd scale right down for half the day and scale up and out at peak times.
Total costs were about 1/2 of what we estimated for bare metal
2 sysadmins for 2 servers? What are they going to do all day? Managing those two servers should probably be 5-10% of their job -- 2-4h per week for each of them seems plenty --, while doing 90-95% other stuff. Like a sibling comment said, "Servers run on electricity, not sysadmin powered hamster wheels." I'm our de facto sysadmin here (university lab) and I spend maybe an hour a week taking care of our ~dozen bare-metal servers.
Be on-call. You need the sysadmins to be available to fix issues when they happen, even if the fixing itself takes little time.
> ... university lab ...
I developed a few web sites for universities, and they were hosted by the university. You really have to hope nothing breaks on Friday afternoon, or you have to wait until Monday morning to get it fixed...
Millions of Facebook accounts are a pretty harmless size metric. DBA workload increases with the number of employees, which is proportional to support requests, accidents, changes, strange needs that need to be addressed, and so on.
Buying and provisioning disks before space runs out is a small part of a DBA's job, and a modest constant-size task compared to predicting how fast space is running out.
Have you got a citation for that claim because that figure seems a little hard to believe.
In terms of your general point: it really depends on your business. In my last job there were 4 DBAs out of 12 total IT staff and they were constantly busy. In my current job there are no DBAs in a much larger team and yet no requirement to need one either. The two businesses produce vastly different products.
That might have worked for the specific hardware BT needed those developers to manage but it's not good advice in the general sense. Systems Administration is as much a detailed speciality as being a software developer. There's so many edge cases to learn -- particularly when it comes to hardening public facing infrastructure -- that you really should be hiring an experienced sysadmin if you're company is handling any form of user data.
As an aside, this is one of the other reasons company directors like the cloud -- or serverless specifically: it absolves responsibility for hardening host infrastructure. Except it doesn't because you then need to manage AWS IAM policies, cloud watch logs and security groups instead of UNIX user groups, syslog and iptables (to name a few arbitrary examples). But that reality is often not given as part of the cloud migration sales pitch.
Clearly in the example above, you can afford to hire two sys admins to manage the bare metal servers (you can probably afford more, but 2 is the minimum that gives some peace of mind)
We had an application that was a glorified quiz engine and our customers would mass enrol and mass take the quizzes so the scaling that was offered by Azure made it a no brainer for us, specially as given the nature of our customers, quizzes would only take place during working hours, so we'd scale right down for half the day and scale up and out at peak times.
Total costs were about 1/2 of what we estimated for bare metal