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1.3 IaaS, PaaS, SaaS and serverless

Describes the cloud landscape as of August 2026

What this is and why it exists

Every cloud product sits somewhere on one spectrum: how much the provider manages versus how much you do. IaaS, PaaS, SaaS and serverless are four points on that spectrum, and being able to place any product on it tells you instantly who patches what — which is the question that decides real incidents.

The vocabulary

  • IaaS (Infrastructure as a Service) — you rent virtual machines, disks and networks; everything above the hardware is yours to run.
  • PaaS (Platform as a Service) — you bring code; the provider runs the operating system, runtime and scaling.
  • SaaS (Software as a Service) — you use finished software over the network; the provider runs everything.
  • Serverless (Functions as a Service) — you bring one function; it runs on demand and you are billed per invocation, not per idle hour.

The mental model

A ladder of surrendered control. On the bottom rung (IaaS) you hold the most control and the most chores: OS patching, runtime upgrades, capacity planning are yours. Each rung up hands a layer of chores — and the control that came with it — to the provider. SaaS is the top rung: nothing to run, nothing to tune, take it as it comes.

Real examples, one per rung: a rented virtual machine is IaaS; a managed app platform where you push code and get a URL is PaaS; a web email suite is SaaS. Serverless is best understood as a billing model rather than a magic trick: the servers exist, but the meter only runs while your function does — which is transformative for spiky workloads and irrelevant for steady ones.

Choosing a model is choosing chores your team can actually carry. A two-person student project has no time for OS patching: start at PaaS or serverless. A team with an operations engineer and unusual requirements may genuinely need IaaS. Moving up the ladder is giving up options you were not using anyway — until the day you need one, which is why the choice deserves a sentence of justification, not a habit.

What you should now be able to explain or do

Place any named product on the spectrum and say who patches the operating system for it. Give a real example of each of the four models. Say when serverless billing wins and when it does not.

Check yourself

IaaS — you. PaaS — the provider. SaaS — the provider, along with everything else.

Servers still run the code; what changes is the meter — you pay per invocation instead of per hour of a machine being on, which only matters when the machine would otherwise sit idle.

PaaS (or serverless): the chores they cannot carry — patching, scaling, capacity — belong to the provider, and what they give up is control they had no time to use.

Control and configurability at each layer the provider takes over — acceptable exactly until you need an option the platform does not expose.

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