Cloud Computing is defined as a style of computing where scalable and elastic IT-enabled capabilities are delivered  as a service to customers (internal or external) using internet technologies.

There are 4 major variants of cloud computing,

Public Cloud

All the resources are commonly shared to all the users who are utilizing that particular public cloud service. Common pool of resources are maintained and distributed to the users depending on their needs. The entire setup will be managed by a cloud provider. Ex: Amazon, Rackspace.

Key Advantage – Very cost effective (compared to other models) – as everything is shared across all the users

Key Disadvantage – Security/Compliance issues

 

Community Cloud

Infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on premise or off premise.

Key Advantage – Security/Domain/Vertical support

Key Disadvantage – Requires support from all participating organizations and lack of ownership.

 

Private Cloud

The cloud infrastructure is operated solely for a particular organization. It may be managed by the organization or a third party and may exist on premise or off premise. In other words, this is exactly the same as public cloud except that the infrastructure and resources are accessible to only one organization. (Ex: VMWare, ScaleMatrix)

Key Advantage – Can implement/follow all the organization norms without any compromise

Key Disadvantage – High Cost

 

Hybrid Cloud

This infrastructure composes of 2 or more of the above mentioned cloud models (public, community or private). The hybrid model provides a unified infrastructure combining all the participating clouds, so that it can be considered as one single cloud with support for data and application portability. This model gives a lot of flexibility as you can mix and match to leverage all the advantages of the above models.

Key Advantage – Flexibility in choosing

Key Disadvantage – High Cost and Additonal need of a Hybrid Cloud Management tool (ex: RightScale, Enstratus)

 

Janakiraman Jayachandran