The same shared-responsibility spectrum from Lesson 1, now with names and concrete scenarios attached. This is the single most scenario-tested idea in Domain 1 — the exam loves to describe a situation and ask which model fits.
From Lesson 1: on which service type are you responsible for installing, configuring, and patching the operating system yourself? Hold that answer — this lesson names it.
All three models sit on one line, trading control for convenience. IaaS gives you the most control and the most responsibility; SaaS gives you the least of both.
| Model | You manage | Provider manages | Best for |
|---|---|---|---|
| IaaS Infrastructure as a Service | OS, patching, network config, database/storage config, apps | Physical hardware, internet connectivity, physical security | Lift-and-shift migrations; test/dev environments you spin up and tear down fast |
| PaaS Platform as a Service | Your application code and data | OS, middleware, dev tools, runtimes, patching & licensing for OS/DB | Building apps on a ready-made framework with built-in scaling/HA; analytics & BI tooling |
| SaaS Software as a Service | Your data, identity/access settings, device access posture | Almost everything — infrastructure, platform, and the application itself | Email, productivity apps, finance/expense tracking — ready to use as-is |
Answering the calibration question: that's IaaS. You're renting hardware — what you install and maintain on top of it is entirely on you.
Rather than asking "define PaaS," the exam typically describes a situation:
Notice the tell: how much of the stack does the sentence imply the customer is willing to touch? More touching → further left (IaaS). Less touching → further right (SaaS).