- LPU MCA Semester 1
- CAP470
- Unit 2
CAP470 · Unit 2: Cloud computing architecture
Service models: IaaS, PaaS and SaaS
10 practice questions · in the MTE and ETE syllabus
Key points
- IaaS gives infrastructure, PaaS a platform, SaaS an application
- Responsibility shifts to the provider up the stack
- EC2 is IaaS, App Engine is PaaS, Gmail is SaaS
- More convenience means less control
The three NIST service models form a stack that shifts responsibility to the provider as you move up.
| Model | Provider supplies | Customer manages | Example |
|---|---|---|---|
| IaaS | virtualized servers, storage, network | OS, runtime, applications, data | Amazon EC2 |
| PaaS | runtime and platform on top of infrastructure | application code and data | Google App Engine |
| SaaS | complete application | only user settings and data | Gmail, Salesforce |
Moving from IaaS to PaaS to SaaS, the provider manages more layers and the customer fewer, giving less operational work but less control. Choose IaaS for full OS control, PaaS to deploy code without managing servers, and SaaS for ready-made applications. Other offerings include Function as a Service (serverless) and Database as a Service.
Exam trap: the developer in PaaS supplies only code, whereas in IaaS they also manage the operating system.
Try two questions
Which statement correctly describes who manages what as you move from IaaS to PaaS to SaaS?
- The customer manages more layers at each step, and the provider fewer
- The provider manages the same layers in every model
- The provider manages more layers at each step
- The customer manages the hardware in every model
Show the answer
C. Responsibility shifts toward the provider from IaaS through PaaS to SaaS.
Why not A: It is the reverse; each step gives more to the provider.
Why not B: The split of responsibility changes with each model.
Why not D: Providers manage physical hardware in all three models.
In which service model does the provider supply a runtime environment so developers can deploy code without managing servers?
- Software as a Service for finished applications
- Infrastructure as a Service for raw servers
- Platform as a Service
- Hardware as a Service for physical devices
Show the answer
C. PaaS provides a managed platform on which customers deploy their own applications.
Why not A: SaaS delivers applications, not a development platform.
Why not B: IaaS leaves operating system and runtime to the customer.
Why not D: This is not one of the three standard service models.