Explain the difference between IaaS, PaaS and SaaS with an example of each.

What the interviewer wants to hear

• IaaS gives raw compute, storage and network; customer manages OS and up
• PaaS manages the runtime and OS; customer deploys code and data
• SaaS is a complete application used by end users
• Responsibility shifts to the provider as you move from IaaS to SaaS
• Gives a correct real example of each

Model answer

These are service models that differ in how much the provider manages. IaaS, Infrastructure as a Service, gives you virtual machines, disks and networks, like Amazon EC2 or Azure Virtual Machines. You manage the operating system, patches, runtime and application. PaaS, Platform as a Service, also manages the OS and runtime, so you just deploy code, for example AWS Elastic Beanstalk, Google App Engine or Azure App Service. SaaS, Software as a Service, is a finished application you simply use, such as Gmail, Microsoft 365 or Salesforce. As you move from IaaS to SaaS you get less control but also less operational work, and the shared responsibility line moves toward the provider. In practice, many teams mix them, for example running containers on a managed Kubernetes service, which sits between IaaS and PaaS.

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