What is the difference between IaaS, PaaS, and SaaS? Give an example of each.
What they are really testing: A pure screen-out: do you understand the shared-responsibility spectrum, who manages what as you move up the stack. They want crisp definitions and the trade-off (control vs operational burden), not memorized acronyms.
A real interview question
What is the difference between IaaS, PaaS, and SaaS? Give an example of each.
What most people say
drag me
“IaaS is infrastructure, PaaS is platform, SaaS is software.”
It just expands the acronyms without the idea behind them, the shared-responsibility spectrum, and gives no examples or trade-off. It tells the interviewer you memorized a slide, not that you understand it.
The follow-ups they ask next
Where do containers and Kubernetes fit on that spectrum?
Containers themselves are infra-ish; managed Kubernetes (EKS/AKS) is often called CaaS, sitting between IaaS and PaaS, you manage workloads and some cluster config, the provider manages the control plane.
Why would a team deliberately choose IaaS over PaaS?
Need for control: specific OS/kernel tuning, licensing, compliance, lift-and-shift of legacy apps, or avoiding a PaaS limitation/lock-in. The cost is they now own patching and scaling.
What the interviewer is listening for
- Leads with the responsibility spectrum
- Gives a concrete example per layer
- Names the control-vs-ops trade-off
What sinks the answer
- Only re-expands the acronyms
- No examples
- Can't say who manages the OS in each
If you genuinely do not know
Say this instead of freezing. Reasoning out loud from what you do know beats silence every single time, and a good interviewer is listening for exactly that.
“They sit on a spectrum of how much you manage. IaaS ([raw VMs, you own the OS up, e.g. EC2]), PaaS ([you ship code, platform runs the rest, e.g. App Service]), SaaS ([finished product you just use, e.g. Gmail]). The trade-off is [control versus operational burden].”
Keep going with cloud fundamentals
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