Azure AZ-900 IaaS, PaaS, and SaaS Guide

Service-type questions on AZ-900 are usually classification tests. The best answer is usually the one that correctly matches how much infrastructure the customer still manages.

IaaS: Infrastructure as a Service, where the provider supplies foundational infrastructure and the customer still manages more of the operating system and application stack.

PaaS: Platform as a Service, where the provider manages more of the platform so the customer can focus more on the application.

SaaS: Software as a Service, where the customer mainly consumes the finished application.

Service-type chooser

Management-boundary table

The management boundary is the point

AZ-900 is not asking which model is “best” in general. It is asking which model fits the requirement:

• if the customer wants more control, IaaS gets stronger
• if the customer wants to focus on the app and not the underlying platform, PaaS gets stronger
• if the customer wants the finished software, SaaS gets stronger

Azure-flavored examples that help

Common traps

• choosing IaaS because it sounds more powerful even when the stem wants less platform management
• choosing SaaS when the team is still building its own application
• answering with a service family before you identify the required management boundary

Decision order that usually wins

1. Ask how much of the stack the customer still manages.
2. Separate infrastructure control from platform hosting and finished application delivery.
3. Use the most managed service model that still fits the requirement.
4. Read use-case clues before choosing the service model.
5. Avoid collapsing IaaS, PaaS, and SaaS into a simple “all cloud is the same” answer.

Quiz