Cloud computing is delivered across three primary service models — Infrastructure as a Service, Platform as a Service, and Software as a Service — each abstracting a different layer of the traditional IT stack and shifting responsibility between the provider and the customer.
IaaS provides virtualized computing resources over the internet, such as virtual machines, storage, and networking. PaaS adds a managed runtime environment on top of that infrastructure, giving developers tools, middleware, and deployment pipelines without managing the underlying servers. SaaS delivers fully functional software applications accessed via a browser or API, where the provider manages everything from infrastructure to the application logic itself.
Each model defines a different boundary between what the provider manages and what the customer is responsible for. With IaaS, the customer manages the OS, runtime, middleware, and applications; the provider only handles physical hardware and virtualization. With PaaS, the provider also manages the OS and runtime, leaving the customer responsible only for application code and data. With SaaS, the provider manages the entire stack and the customer simply configures and uses the application.
AWS EC2, Google Compute Engine, and Azure Virtual Machines are canonical IaaS examples, suited for teams that need fine-grained control over their environment. Heroku, Google App Engine, and AWS Elastic Beanstalk are PaaS platforms ideal for developers who want to focus on writing code without worrying about infrastructure provisioning. Salesforce, Google Workspace, Slack, and Dropbox are SaaS products used by end-users and businesses without any infrastructure management overhead.
Choose IaaS when you need maximum flexibility, custom OS configurations, or are migrating legacy workloads to the cloud. Choose PaaS when your team wants to accelerate development velocity and avoid operational overhead for standard application hosting scenarios. Choose SaaS when you need a ready-made solution for a standard business function such as email, CRM, or collaboration, and customization at the code level is not required.
A common mistake is selecting IaaS for every use case out of a desire for control, which creates unnecessary operational burden and slows delivery. PaaS platforms can introduce vendor lock-in because your deployment model becomes tightly coupled to provider-specific runtimes and APIs — evaluate portability before committing. With SaaS, data governance and compliance are critical concerns since your data resides entirely on third-party infrastructure, so always review the provider's security certifications, data residency policies, and SLAs carefully.
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