[crabmusket]

I can't have my database on a separate Linux box? Seems odd to insist on either precisely one server or go straight to container orchestration.

That said, I agree with you about the other generalisations!

EDIT: actually, where do PaaSes fit into this taxomony? I'd argue that level 2 is actually the PaaS level. You might choose an edge PaaS (Workers), distributed (Fly.io), or centralised (Elastic Beanstalk) depending on your needs. But ultimately this level is: "I write code, you run it". FaaSes are a subset of PaaS providers which focus on stateless models, but there's no reason you can't combine FaaS for your code with a managed database offering.

[NikolaNovak]

I assumed that option 3 was a "Fermi estimation", I. E. "single handed number of servers"

I'm used to 3 tier legacy apps (web / app / dB) but I assumed that would fit into number 3 the best, I could be wrong...

[crabmusket]

Maybe it's "on the order of a single server", or conveys that the servers are "statically" arranged and/or manually managed rather than automatically (auto scaling, service discovery)?

[hathawsh]

Yeah, that's a better way to put it. #3 is a static arrangement of a small number of servers.