(IaaS)Infrastructure as a service (IaaS) is the most flexible category of cloud services, as it provides you with the maximum amount of control for your cloud resources. In an IaaS model, the cloud provider is responsible for maintaining the hardware, network connectivity (to the internet), and physical security. You’re responsible for everything else: operating system installation, configuration, and maintenance; network configuration; database and storage configuration; and so on. With IaaS, you’re essentially renting the hardware in a cloud data centre, but what you do with that hardware is up to you.
(PaaS)Platform as a service (PaaS) is a middle ground between renting space in a data centre (infrastructure as a service) and paying for a complete and deployed solution (software as a service). In a PaaS environment, the cloud provider maintains the physical infrastructure, physical security, and connection to the internet. They also maintain the operating systems, middleware, development tools, and business intelligence services that make up a cloud solution. In a PaaS scenario, you don't have to worry about the licensing or patching for operating systems and databases.
PaaS is well suited to provide a complete development environment without the headache of maintaining all the development infrastructure.
(SaaS)Software as a service (SaaS) is the most complete cloud service model from a product perspective. With SaaS, you’re essentially renting or using a fully developed application. Email, financial software, messaging applications, and connectivity software are all common examples of a SaaS implementation.
While the SaaS model may be the least flexible, it’s also the easiest to get up and running. It requires the least amount of technical knowledge or expertise to fully employ.
Use cases:(IaaS)
Lift-and-shift migration: You’re standing up cloud resources similar to your on-prem datacenter, and then simply moving the things running on-prem to running on the IaaS infrastructure.Testing and development: You have established configurations for development and test environments that you need to rapidly replicate. You can stand up or shut down the diο¬erent environments rapidly with an IaaS structure while maintaining complete control.(PaaS)Development framework: PaaS provides a framework that developers can build upon to develop or customize cloud-based applications. Similar to the way you create an Excel macro, PaaS lets developers create applications using built-in software components.Analytics or business intelligence: Tools provided as a service with PaaS allow organizations to analyze and mine their data, finding insights and patterns and predicting outcomes to improve forecasting, product design decisions, investment returns, and other business decisions.(SaaS)Email and messaging.Business productivity applications.Finance and expense tracking.