Service models of cloud computing:

SPI is an acronym for the most common cloud computing service models, Software as a Service, Platform as a Service and Infrastructure as a Service

• Infrastructure- as- a – Service (IaaS) :

  a. It is a way of delivering Cloud Computing infrastructure – servers, storage, and network, operating systems – as an on demand service.

  b. Infrastructure as a Service is sometimes referred to Hardware as a Service (HaaS).

  c. Leading vendors that provide Infrastructure as a Service are Amazon EC2, Amazon S3, RackSpace Cloud Servers and Flexiscale.

• Platform-as-a-Service (PaaS):

  a. It is a paradigm for delivering operating systems and associated services over the Internet without downloads and installations.

  b. 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.

  c. Some examples of PaaS include Google Application Engine, Microsoft Azure Services and the Force.com.

  d. Advantages of PaaS are:

  • Operating System features can be changed and upgraded frequently.

  • Geographically distributed development teams can work together on software development projects.

  • Services can be obtained from diverse sources that cross international boundaries.

• Software-as-a-Service (SaaS):

1. It is a software distribution model in which applications are hosted by a vendor or service provider and made available to customers over a network, typically the Internet.

2. An example of SaaS is Microsoft Office365. With Office365 Word can be acquired for a small monthly fee, with no client installation, the files are automatically backed up, software upgrades are automatically received and the software can be accessed from anywhere.

3. SaaS delivers a packaged or equivalent commercial software application to end users over the Internet with a subscription or usage-based pricing model, as opposed to traditional lifetime license for a particular version.

Deployment models (Development Models) of Cloud Computing:

• Public Cloud

1. A public cloud is one based on standard cloud computing model, in which a service provider makes resources, such as applications and storage, available to an enterprise over the Internet.

2. The enterprise and storage service provider are separate and the data is stored outside of the enterprise’s data center thus freeing them from the expensive costs of having to purchase, manage and maintain on-premises storage hardware and software resources.

3. The main benefits of using a public cloud service are:

   • Easy and inexpensive set-up because hardware, application and bandwidth costs are covered by the provider.

   • Scalability to meet needs

   • No wasted resources because you pay for what you use.

4. Examples of public cloud include Amazon Elastic Compute Cloud (EC2), IBM’s Blue Cloud, Sun Cloud, Google App Engine and Windows Azure Services Platform.

• Private Cloud:

1. The private cloud or an internal cloud is a proprietary cloud computing platform that is implemented within the corporate’s firewall, under the control of the IT department.

2. Private clouds are more secure as compared to public clouds but the organization implementing the private cloud is responsible for running and managing IT resources instead of passing that responsibility on to a third party cloud provider.

3. Advances in virtualization and distributed computing have allowed corporate networks and datacenter administrators to effectively become service providers that meet the needs of their customers within the corporation.

• Hybrid cloud:

1. Some organizations may host critical applications on private clouds and applications with relatively less security concerns on the public cloud. The usage of both private cloud and public clouds together is called hybrid cloud.

2. A related term is Cloud Bursting in which organizations use their own computing infrastructure for normal usage but access the cloud using services such as Sales force cloud computing for high/peak load requirements. This ensures that a sudden increase in computing requirement is handled gracefully.

• Community Cloud

1. This involves sharing of computing infrastructure in between organizations of the same community.

2. For example, all government organizations within a particular state may share computing infrastructure on the cloud to manage data related to citizens residing in the states.

3. Additional variations of the four base cloud deployment models can exist.

Examples include:

• Virtual Private Cloud - Also known as a "dedicated cloud" or "hosted cloud," this model results in a self-contained cloud environment hosted and managed by a public cloud provider, and made available to a cloud consumer.

• Inter-Cloud - This model is based on an architecture comprised of two or more inter-connected clouds.

Explain different cloud service deployment models

1) Private cloud:-
i) The cloud infrastructure is provisioned for exclusive use by a single organization comprising multiple consumers (e.g., business units).
ii) It may be owned, managed, and operated by the organization, a third party, or some combination of them , and it may exist on or off premises.

2)Community cloud:-
i) The cloud infrastructure is provisioned for exclusive use by a specific community of consumers from organizations that have shared concerns (e.g., mission, security requirements, policy, and compliance considerations).
ii) It may be owned, managed, and operated by one or more of the organizations in the community, a third party, or some combination of them, and it may exist on or off premises.

3)Public cloud:-
i) The cloud infrastructure is provisioned for open use by the general public.
It may be owned, managed, and operated by a business, academic, or government organization, or some combination of them.
ii) It exists on the premises of the cloud provider.

4)Hybrid cloud:-
i) The cloud infrastructure is a composition of two or more distinct cloud infrastructures (private, community, or public) that remain unique entities, but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load balancing between clouds).
ii) The cloud infrastructure is provisioned for open use by the general public.
iii) It may be owned, managed, and operated by a business, academic, or government organization, or some combination of them.
iv) It exists on the premises of the cloud provider.