3.2: Cloud Service Models- IaaS, PaaS, SaaS

One of the core ways to categorize cloud offerings is by service model – essentially, what layer of the computing stack is provided “as a service” by the vendor versus managed by the customer. The three primary cloud service models are Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS). All share the cloud’s key characteristics (on-demand, scalable, network-accessible, pay-as-you-go), but differ in the level of abstraction and control given to the user.

Service Model Summary: Often, these three models are depicted as a stack or continuum of control. In a fully on-premises scenario, an organization manages everything (from physical network up to applications). In IaaS, management of hardware is outsourced, but OS and above are customer-managed. In PaaS, even the OS and runtime are outsourced, leaving only the application. In SaaS, the entire stack is outsourced to the provider. It’s worth noting these models are not mutually exclusive – many enterprises use all three simultaneously for different needs . For example, a company might use IaaS (AWS EC2) for some custom systems, PaaS (Azure App Service) for a new web app project, and multiple SaaS apps (Salesforce, Workday, etc.) for standard business functions. As cloud services matured, more granular models also emerged, such as Functions as a Service (FaaS) or serverless computing (where you deploy code functions and the platform runs them on demand), and Containers as a Service (CaaS) (container runtimes/orchestration managed by provider). These can be seen as specialized extensions of PaaS and IaaS, respectively.

The key takeaway is that service models determine how much of the computing stack you manage versus how much you offload to the provider. Businesses must choose the right model for each workload based on desired control, flexibility, and responsibility.

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