Service Model of Cloud Computing:

Cloud computing providers offer their services according to three fundamental models: Infrastructure as a service (IaaS), platform as a service (PaaS), and software as a service (SaaS) where IaaS is the most basic and each higher model abstracts from the details of the lower models.

1. Software as a Service (SaaS)

SaaS is a methodology for delivering software from the cloud without downloading and installing it on your computer. Software as a Service (SaaS) is an emerging software architecture where major applications are hosted remotely and accessed via a web browser. As a user, you don't need to worry to manage or upgrade the tool.

To better describe the concept, let's use the analogy of buying a suit. Using SaaS is like going to a department store and buying a suit off the rack. You can find something quite nice that's already made and wear it to a party that night. You could also have a tailor make minor adjustments to get a more customized fit.

These are on-demand end-user software applications like Google Apps, Salesforce.com’s CRM, business management services, etc. Example: Google Apps (Google Docs), and SalesForce.com are among the providers of this kind of cloud computing.

2. Platform as a Service (PaaS)

PaaS allow the user to create their own cloud applications using supplier-specific tools and languages means with the help of PaaS we can customize the application according to the requirement. 

An environment to build, operate and administer an application without managing the complex functionalities of cloud infrastructure is known as PaaS.

In the clothing world, this approach is akin to going to a bespoke store where you pick out the fabric, buttons, and pattern and have the tailor make a suit that is custom fit to you. You want a yellow polka-dotted, three-piece suit? You don't have to wait for Armani to realize it's the next hot look; you can have it made to measure! You won't be able to wear it to a party tonight, but you can believe it'll be a perfect fit when it's done. And no one else will have anything like it

Some Examples of PaaS as below

– Heroku

– Sales Force Lightning Platform

– Google App Engine

3. Infrastructure as a Service (IaaS)

IaaS is a model that provides just the hardware resources to its users over the cloud. The benefits include cost savings and scalability. Infrastructure as a Service is also referred to as Hardware as a Service (HaaS). The Heroku platform itself is actually built on top of a powerful IaaS called Amazon Web Services (AWS). AWS allows you to assemble virtual machines, load balancers, and other low-level resources to build large and complex application clusters. These systems require highly skilled professionals to architect, build, monitor, and maintain, but are more customizable than Platforms.

If you were to approach suit-making with the IaaS model, you would have to buy the fabric, buttons, and thread for yourself, dream up the designs for your custom suit, and cut the fabric to the pattern. Then you have to pay the local sewing shop to rent time on a sewing machine and sew the suit yourself.