Introduction

Cloud computing is a type of computing that relies on sharing computing resources rather than having local servers or personal devices to handle applications. Cloud computing allows consumers and businesses to use applications without installation and access their personal files at any computer with internet access.

Service Model

The service model on which you will host your application(s), for example, IaaS, PaaS, or SaaS. Each of these service models requires various levels of support and responsibilities once a system is deployed to the platform. To resolve the future challenges that you might encounter you need to understand the models carefully.
Every service model offers you some kind of resource required to operate the most web-enabled systems imaginable.
Before diving into each of the service models, let's have a look at the layered structure Of cloud computing.

Infrastructure as a Service (IaaS)

Infrastructure as a Service (IaaS), as the name suggests, provides you the computing infrastructure, physical or (quite often) virtual machines, and other resources like virtual-machine disk image library, block and file-based storage, firewalls, load balancers, IP addresses, virtual local area networks and so on. Infrastructure as a Service (Iaas) is a way of delivering Cloud Computing infrastructure as an on-demand service. Rather than purchasing servers, software, data center space, or network equipment, clients instead buy those resources as a fully outsourced service on demand. As you can see, in the IaaS service model the providers get to manage the network, storage, servers, virtualization and operating system (only up to a level), and you get to manage the OS, middleware, runtime, data, and applications.
The following are the key features of an IaaS:
  • Resources are distributed as a service
  • Allows for dynamic scaling
  • Generally includes multiple users on a single piece of hardware
Examples include:
  • Windows Azure
  • Amazon EC2
  • Rack Space

Platform as a Service (PaaS)

Platform as a Service (PaaS) provides you computing platforms and that typically includes an operating system, programming language execution environment, database, web server, and so on. PaaS is analogous to SaaS, except that rather than being software delivered over the web; it is a platform for the creation of software, delivered over the web.
The following are the key features of PaaS:
  • Services to develop, test, deploy, host, and maintain applications in the same integrated development environment. All the varying services are necessary to fulfill the application development process.
  • Web-based user interface creation tools help to create, modify, test, and deploy various UI scenarios.
  • Multi-tenant architecture where multiple concurrent users utilize the same development application.
  • Built-in scalability of deployed software including load balancing and failover.
  • Integration with web services and databases via common standards.
  • Support for development team collaboration. Some PaaS solutions include project planning and communication tools.
  • Tools to handle billing and subscription management.
The following are examples:
  • Google App Engine.
  • Force.com
  • AWS Beanstalk
  • Hero Ku

Software as a Service (SaaS)

Any software deployed over the internet comes under the SaaS service model. With SaaS, a provider (for example Gmail / Office 365) licenses an application to customers either as a service on-demand, through a subscription, in a “pay-as-you-go” model, or (increasingly) at no charge when there is an opportunity to generate revenue from streams other than the user, such as from advertisement or user list sales.
In the SaaS model you are provided with access to application software often referred to as on-demand software. You don't need to worry about the installation, setup and running of the application. The service provider will do that for you. You just need to pay and use it using some client.
The following are the key features of a SaaS:
  • Web access to commercial software
  • Software is managed from a central location
  • Software delivered in a “one-to-many” model
  • Users are not required to handle software upgrades and patches
  • Application Programming Interfaces (APIs) allow for integration among various pieces of software
The following are examples:
  • Google Apps
  • Office 365
  • Email Applications (Gmail / Hotmail / Yahoo and so on)
  • Finance Management Applications
  • CRM (Customer Relationship Management) applications

Types of cloud computing

Basics types of cloud in cloud computing:
  • Private cloud
  • Public cloud
  • Hybrid cloud

Private cloud

A Private Cloud is implemented using a dedicated data center infrastructure of hardware and software that is used privately by an organization. The data center can be on-premises or off-premises. It is not shared with another organization.

Public cloud

A Public Cloud is implemented using a shared data center infrastructure of hardware and software that is shared by multiple organizations. The data center is off-premises.
The following figure uses Customer Relationship Management (CRM) Software as a Service (SaaS) to illustrate a Public Cloud.

Hybrid cloud

A Hybrid Cloud is any combination of Clouds. It could be a Private Cloud and one or more Public Clouds. Similarly, it could be a Virtual Private Cloud and one or more Public Clouds. It is, however, more than just multiple Clouds. There need to be resources shared among the Clouds. An example is Cloud Bursting.
The following figure is one example of a Hybrid Cloud. It uses Customer Relationship Management (CRM) Software as a Service (SaaS) to illustrate a Hybrid Cloud.
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