Cloud Computing refers to the concept in which computing power is obtained as a service, without users having immediate access to physical resources such as processors, memory, or hard disk. Rather than residing in a “physical” box with fixed resources, compute resources are located in a virtual environment (the cloud) where the resources can be limitless.
Public Cloud and private clouds are extremely similar. Hybrid Clouds are a combination of Public and Private Clouds.
A cloud is considered a 'Public cloud' when the services are provided over a network that is open for public use. While technically there is no difference between public and private cloud architecture, security consideration, however, may be substantially different for services (applications, storage, and other resources) that are made available by a service provider for a public audience and when communication is effected over a non-trusted network. Generally, public cloud service providers like ProfitBricks, Amazon AWS, and others own and operate the infrastructure and offer access only via Internet.
“Private cloud” is cloud infrastructure operated solely for a single organization, whether managed internally or by a third-party and hosted either internally or externally. Undertaking a private cloud project requires a significant level and degree of engagement to virtualize the business environment, and requires the organization to reevaluate decisions about existing resources.
A hybrid cloud is composed of two or more clouds (private or public) that remain unique, individual entities that are bound together, offering the benefits of multiple deployment models. Hybrid models expand deployment options for cloud services, allowing IT organizations to use public cloud computing resources to meet temporary needs. This capability enables hybrid clouds to employ cloud bursting for scalability across the cloud.
Cloud computing relies on sharing of resources to achieve coherence and economies of scale similar to a utility (like the electricity grid) over a data communications network. At the foundation of cloud computing is the broader concept of converged infrastructure and shared services.
The cloud focuses on maximizing the effectiveness of the shared resources. Cloud resources are typically not only shared by multiple users but as well as dynamically re-allocated as per demand. This can work for allocating resources to users in different time zones. This approach should maximize the use of computing powers thus reducing environmental damage as well, since less power, air conditioning, data center rack space, etc. is required for the same functions.
The term "moving to cloud" also refers to an organization moving away from a traditional CAPEX model (buy the dedicated hardware and depreciate it over a period of time) to the OPEX model (use a shared cloud infrastructure on a pay as you use it basis).
Cloud computing allows companies to avoid upfront infrastructure costs, and focus on projects that differentiate their businesses and propel it forward, instead of infrastructure. Additionally, cloud computing allows enterprises to get their software applications up and running faster, with improved manageability and less maintenance, allowing IT teams to rapidly adjust compute resources to meet fluctuating and unpredictable business demand.