Understanding IaaS, PaaS, and SaaS: Cloud Service Models Explained

In a previous article we introduced cloud computing, noting that different users need different levels of service, ranging from simple server rentals to full‑stack solutions. Cloud computing can be divided into three service models—Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS)—often called the cloud stack because they build on top of each other.

IaaS (Infrastructure as a Service) provides virtualized computing resources over the network and charges based on actual usage. It is analogous to a shared kitchen where the provider supplies the kitchen, appliances, and utilities, while the user brings their own ingredients and cooks the dishes. Users can deploy any software, including operating systems and applications, on the provider’s infrastructure, managing the OS, storage, and network components, but not the underlying hardware.

PaaS (Platform as a Service) offers a complete development and deployment platform. Extending the kitchen analogy, the provider also supplies pre‑washed, chopped vegetables, seasoned meat, and dough, so users only need to cook or assemble the final dish. PaaS lets developers use the provider’s programming languages, libraries, services, and tools to build and deploy applications without managing the underlying infrastructure such as servers, networks, or operating systems.

SaaS (Software as a Service) delivers ready‑to‑use software over the internet. In the analogy, SaaS is like an online food‑delivery service that provides fully prepared meals; users simply pay and enjoy the dishes without any cooking. SaaS applications run on the provider’s infrastructure and are accessed via web browsers or APIs. Users do not manage any underlying hardware, OS, or even the application itself, except for limited configuration settings. The article also outlines a SaaS maturity model ranging from custom‑built single‑tenant solutions to multi‑tenant, multi‑instance architectures that enable near‑infinite horizontal scaling.

Summary : The article uses the kitchen analogy to clarify the three cloud service models—IaaS provides the basic infrastructure, PaaS adds a development platform, and SaaS delivers complete applications. As the stack moves upward, the provider’s responsibilities increase while the user’s workload decreases. Common examples include Amazon EC2 for IaaS, Heroku for PaaS, and Gmail or PayPal for SaaS.

From IaaS to PaaS to SaaS, the services offered become richer while the amount of work the user must perform (highlighted in green in the diagram) continuously diminishes.

Typical products: IaaS – Amazon EC2, Alibaba Cloud; PaaS – Heroku; SaaS – Gmail, PayPal.