**2.3 Infrastructure as a service (IaaS)**

IaaS facilitates availability of the IT resources such as server, processing power, data storage and networks as an on demand service. Here user of this service can dynamically choose a CPU, memory storage configuration according to needs. A cloud user buys these virtualized and standardized services as and when required.

**3**

*Introductory Chapter: Cloud Computing Security Challenges*

For example, a cloud customer can rent server time, working memory and data storage and have an operating system run on top with applications of their own choice.

Furthermore, these services can be deployed into Public Clouds, Private Clouds

In the Public Cloud delivery mode, all the physical infrastructure are owned by the provider of the services which were provided off-site over the Internet hosted at cloud vendor's premises. Here the customer has no control and limited visibility over where the service is hosted as all these massive hardware installations are distributed throughout the country or across the globe seamlessly. This massive size enables economies of scale that permit maximum scalability to meet varying requirements of different customers and thus provides greatest level of efficiency, maximum reliability through shared resources but with rider cost of added

In case of Private Cloud mode, entire infrastructure is owned, managed and operated exclusively by the organization or by a third-party vendor or both together and is hosted on the organization premise using virtualization layer. It also facilitates flexibility, scalability, provisioning, automation and monitoring and thus offers the greatest level of control, configurability support, high availability or fault tolerant solutions and advanced security which is missing in public cloud. Basically, very concept of private clouds is driven by concerns around security and keeping assets within the firewall which results it to significantly more expensive with typi-

As name suggest, Hybrid Cloud includes a variety of product mix from both Public and Private Cloud options sourced from multiple providers at added cost to keep track of multiple different security platforms by ensuring all aspects of business to communicate with each other seamlessly. In case of Hybrid approach, operational flexibility, scalability, efficiency and security are properly balanced by hosting mission critical applications and sensitive data protected on the Private Cloud and generic application development, big data operations on non-sensitive data and testing on the Public Cloud. Hybrid Cloud thus leverage benefits of both Public and Private Cloud by maintain balance between the efficiency, cost saving,

The combination of the different service and deployment models enables different business models with new business roles. A cloud service is likely to have many layers of abstraction that build on top of each other with define roles and duties. Accessibilities of these predefine services to the end user depends on the different service model. Abstraction layers of standard Cloud model is depicted in adjoining **Figure 2**. Service providers may adapt and compose several services into one, which

or Hybrid Clouds; each has its own advantages and disadvantages.

*DOI: http://dx.doi.org/10.5772/intechopen.92544*

**3. Types of deployments**

**3.1 Public cloud**

vulnerability.

**3.2 Private cloud**

**3.3 Hybrid cloud**

cally modest economies of scale.

security, privacy, and control.

is then offered to the cloud customers.

For example, a cloud customer can rent server time, working memory and data storage and have an operating system run on top with applications of their own choice.
