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Infrastructure as a Service (IaaS) Fundamentals

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Cloud concepts

Infrastructure as a Service (IaaS) Fundamentals

Short Summary

Infrastructure as a Service (IaaS) is a cloud service model where you rent basic infrastructure—servers, storage, and networking—and keep significant control over how it runs. The cloud provider maintains the physical datacenter, hardware, and physical security, while you manage the operating system (OS), configuration, and what you deploy on top. This lesson helps you recognize IaaS in real situations and separate it from Platform as a Service (PaaS) and Software as a Service (SaaS).

Learning Objectives

By the end of this lesson, you will be able to:

  • Define Infrastructure as a Service (IaaS) in simple terms.
  • Describe the responsibility split in IaaS between the provider and you.
  • Identify common scenarios where IaaS is a good fit (for example, lift-and-shift and test/dev).
  • Differentiate IaaS from Platform as a Service (PaaS) and Software as a Service (SaaS) using “who manages what” clues.

Core Concepts

Infrastructure as a Service (IaaS) provides on-demand access to computing resources such as servers, storage, and networks. In practice, this often looks like creating Virtual Machines (VMs), attaching storage, and configuring networking—without buying or maintaining physical hardware.

In an IaaS model, the cloud provider is responsible for maintaining the physical side of the environment (hardware, physical security, and the underlying connectivity to the internet). You don’t rack servers, replace disks, or run the physical datacenter.

You are responsible for “everything else” above that physical layer. That typically includes operating system installation, configuration, and maintenance (including patching and updates), plus your network, database, and storage configuration choices, and the security of what you deploy and run.

A practical rule of thumb for beginners: if you manage the OS, you’re usually in IaaS. If the provider manages the OS and runtime environment and you focus on deploying code and managing data, you’re leaning toward PaaS. If you simply use a finished application that the provider manages, that’s SaaS.

IaaS often gives you the most flexibility and control, but it also comes with more operational work compared to PaaS and SaaS. It’s a strong fit when you need VM-level control, want to move existing systems with fewer changes, or need to replicate environments quickly.

Practical Understanding

Practical Situation 1: “I need to move a server with minimal changes”

A team wants to move an existing on-premises server into the cloud and keep OS-level control, installed software, and configuration similar to what they had before.

How to think about it: This is a classic IaaS scenario: you’re essentially “renting the hardware,” but what runs on that hardware is still your responsibility. You keep control of the OS and the software stack, while the provider handles the physical environment.

Common misunderstanding: “Because it’s in the cloud, the provider will patch my server OS.” In IaaS, OS patching and updates are still on you.

Practical Situation 2: “I need test/dev environments fast, and I want full control”

A team needs to spin up and tear down repeatable dev/test environments quickly while keeping control over configuration.

How to think about it: IaaS can be a good match because you can replicate environments rapidly while still controlling OS and configuration. You get speed from on-demand provisioning, but you still manage the parts of the stack above the physical layer.

Common misunderstanding: “IaaS means no management work.” IaaS removes physical hardware work, but it does not remove operating and securing your environment.

Practical Situation 3: “Is this offering IaaS, PaaS, or SaaS?”

You’re looking at a VM service, a managed app hosting platform, and a productivity suite, and you want a quick way to classify them.

How to think about it: Use the “control clue”:

  • Manage the OS → think IaaS (for example, VMs).
  • Deploy code while the provider manages OS/runtime → think PaaS (for example, managed app platforms).
  • Use a complete application → think SaaS (for example, email/office tools).

Common misunderstanding: “Anything in the cloud is IaaS.” The model depends on how much of the stack you manage versus what the provider manages.

Common Pitfalls

  • Mistake: Assuming IaaS means “no management needed.” Correction: In IaaS, you still manage and secure the OS and what runs on it; only the physical infrastructure is handled by the provider.

  • Mistake: Forgetting the provider/customer split and blaming the provider for OS patching issues. Correction: The provider maintains the physical environment; you handle OS installation, configuration, patching, and updates.

  • Mistake: Misclassifying PaaS as IaaS just because you deploy something to it. Correction: If the provider manages the OS/runtime and you focus on apps and data, that’s typically PaaS, not IaaS.

  • Mistake: Thinking “VM = on-prem in the cloud” and ignoring cloud-specific networking and security configuration. Correction: Even with VMs, you still need to configure networking and security choices appropriately; the cloud just changes how you do it.

  • Mistake: Using IaaS by default for everything. Correction: Choose IaaS when you need OS-level control; choose PaaS or SaaS when you want the provider to manage more of the platform or the application.

Check Your Understanding

  1. In your own words, describe what you “rent” in IaaS and what you still manage.
  2. List three responsibilities the provider typically handles in IaaS and three responsibilities you typically handle.
  3. Why is “who manages the OS” a useful clue for distinguishing IaaS from PaaS and SaaS?
  4. Describe a lift-and-shift scenario and explain why IaaS fits it.
  5. Name one case where IaaS is the better choice and one case where PaaS or SaaS is the better choice. Explain your reasoning.

Further Reading