1.3. Cloud Service Models: IaaS, PaaS, SaaS
First Principle: Cloud service models define the level of management and control shared between the cloud provider and the customer. Understanding these models is fundamental to choosing the right service to balance control, development speed, and operational overhead.
What It Is: IaaS, PaaS, and SaaS are the three main categories of cloud computing services, each offering a different degree of abstraction.
- Infrastructure as a Service (IaaS):
- Description: Provides fundamental computing resources (virtual machines, networking, storage). You manage the OS, applications, and data.
- Analogy: Renting the land and building materials. You build the house yourself.
- Example: Azure Virtual Machines.
- Platform as a Service (PaaS):
- Description: Provides a managed environment for app development and deployment. Azure manages the OS, runtime, and middleware. You manage your application code and data.
- Analogy: Renting a house where the foundation, walls, and utilities are already built. You just furnish it.
- Example: Azure App Service, Azure SQL Database.
- Software as a Service (SaaS):
- Description: Ready-to-use applications delivered over the internet, managed entirely by the provider. You only use the software.
- Analogy: Renting a fully furnished and serviced apartment.
- Example: Microsoft 365, Salesforce.
Shared Responsibility Model in Service Models:
| You Manage | Microsoft Manages |
|---|---|
| On-Premises: Applications, Data, Runtime, Middleware, OS, Virtualization, Servers, Storage, Networking | (None) |
| IaaS: Applications, Data, Runtime, Middleware, OS | Virtualization, Servers, Storage, Networking |
| PaaS: Applications, Data | Runtime, Middleware, OS, Virtualization, Servers, Storage, Networking |
| SaaS: (User-specific configurations) | Applications, Data, Runtime, Middleware, OS, Infrastructure |
Scenario: A company wants to migrate a legacy application that requires a specific OS configuration. They also want to build a new web API that needs to scale automatically without them managing servers.
Reflection Question: Which cloud service model (IaaS, PaaS, or SaaS) would be most appropriate for each of these two scenarios, and why? How does the shared responsibility change between them?
š” Tip: Remember the pizza-as-a-service analogy.
IaaS is like buying the ingredients and using someone else's kitchen. PaaS is like ordering a pizza for delivery. SaaS is like going out to a restaurant to eat pizza.