IaaS vs PaaS vs SaaS

Three categories of cloud computing

📝 IaaS, PaaS, SaaS.
Allows using a combination of these types of infrastructure.
- E.g. Microsoft 365 Apps on company computers (SaaS), VMs (IaaS) on Azure and Azure SQL Database (PaaS) to store your data.

Instant computing infrastructure, provisioned and managed over the internet.
Aims to give you the most control over the provided hardware that runs your application
📝 E.g. virtual machines (VMs), storage, and operating systems.
You rent hardware instead of buying
Ensuring that a service is up and running is a shared responsibility (see shared responsibility model)
- cloud provider ensures the cloud infrastructure is functioning correctly
- cloud customer ensures the service they are using is
  - configured correctly
  - up to date
  - available to their customers.

Migrating workloads: Managed similar to on-prem infrastructure & provides easy migration path.
Test and development: Teams can quickly set-up & dispose test/dev environments with fast & economical scaling.
Storage, backup and recovery: Organizations avoid the capital outlay and complexity of storage management.
- Useful for managing unpredictable demand and steadily growing storage needs.
- can also simplify the planning and management of backup and recovery systems.

Provides an environment for building, testing, and deploying software applications
- Can add features such authentication.
Aims to help creating an application quickly without managing the underlying infrastructure.
- 📝 E.g. for a web app / Azure SQL databases you don’t need to install an operating system, web server, or even system updates.
Resources are purchased on a pay-as-you-go basis and accessed over a secure Internet connection.

Lets developers create applications using built-in software components.
📝 Cloud features such as scalability, high-availability, and multi-tenant capability are included
Reducing the amount of coding that developers must do.

Tools provided as a service with PaaS allow organizations to analyze and mine their data.
They can find insights and patterns, and predict outcomes to improve business decisions such as forecasting, product design, and investment returns.

Software that is centrally hosted and managed for the end customer.
Usually based on an architecture where one version of the application is used for all customers
Usually licensed through a monthly or annual subscription
📝 E.g. Office 365, Skype, and Dynamics CRM Online.

	IaaS	PaaS	SaaS
Upfront costs	None, pay for what you use	None, pay for what you use	None, monthly / annual subscription
User ownership	purchase, installation, configuration, and management of their own software, operating systems, middleware, and applications	development of their own applications	not responsible for any maintenance or management of that software.
Cloud provider ownership	underlying cloud infrastructure (such as virtual machines, storage, and networking) is available for the user.	operating system management, network, and service configuration.. typically everything except user application	provision, management, and maintenance of the application software

These categories are layers on top of each other
- Abstraction order: SaaS > PaaS > IaaS
- Abstraction = Hide details, quicker production but less control over the underlying hardware.
IaaS: user is responsible for managing the operating systems, data, and applications.
PaaS: user is responsible for the applications and data they run and store.
SaaS: user just uses the software.

shared responsibility model