Cloud Computing Service Models

“As a Service” are cloud computing service offerings or models.
It is the way in which the IT assets are consumed in these offerings.
The cloud service providers manages all the IT infrastructure like hardware, servers, software, development tools.
Examples: IaaS, PaaS and SaaS.

Cloud services provide the IT infrastructure as a service to the users without having to manage the traditional on-premise IT infrastructure like hardware, servers, software, development tools.
Cloud services are quicker, easier to manage and setup.
Cloud services are cost effective.
Cloud services provide better security.

Infrastructure as a Service is on-demand cloud-hosted computing infrastructure like servers, storage capacity, networking resources.
With this users have full control over the fundamental infrastructure and configure it based on their needs.
Examples: AWS EC2, Google Cloud Platform, Microsoft Azure.

Platform as a Service providers users with platform to build, develop, and manage applications without having to manage the underlying infrastructure.
It provides servers, OS, storage, networking, databases, middlewares, runtimes, frameworks, development tools, and is also responsible for security patches, software upgrades, buckups and more.
Examples: AWS Elastic BeanStack, Google App Engine, Microsoft Windows Azure.

Software as a Services provides users access to software applications that are hosted on the cloud and are accessible through mobile apps, or web browsers.
Users pay monthly or yearly fees to use the application.
The underlying infrastructure is hosted and managed by the SaaS vendor.
Example: Slack, Google Mail, Dropbox, Salesforce, etc.

Here is an example to illustrate the difference between the three. Suppose you want to build a website.

With IaaS, you would rent out virtual servers from AWS or Google Cloud. Install and configure it to run necessary web server software, hosting environment, OS, or any other softwares to run the website.
With PaaS, you would use a platform such as Heroku, or Google App Engine, which provides preconfigure environments for running web applications. You would simply upload you code, and the platform would handle everything, including scaling and managing resources.
With SaaS, you would use a service like Squarespace or Wix which provides web-based interface to create and manage websites. You don’t need to know coding or servers for building websites.