Cloud computing ( cloud is computing ) - a model of enabling ubiquitous and convenient network access on demand to a pool shared of configurable computing resources (eg, networks, servers, storage, applications and services) that can be rapidly made available and released with minimal management effort or interaction with the provider (supplier). This cloud model is represented (described) by five main characteristics, three service models and four deployment models.

The main characteristics of cloud computing that distinguish them from other types of computing (Internet resources):

Self-service on demand. The consumer, as necessary, automatically, without interaction with each service provider, can independently determine and change computing power, such as server time, data storage capacity.

Wide (universal) network access. Computing capabilities are available over long distances through the network through standard mechanisms, which promotes the widespread use of heterogeneous (thin or thick) client platforms (terminal devices).

Pooling resources Configurable computing resources of the supplier are combined into a single pool for sharing distributed resources by a large number of consumers.

Instant resource elasticity (instant scalability). Cloud services can be quickly provided, expanded, compressed, and released based on customer needs.

Measured service (accounting of consumed service and the ability to pay for services that were actually used). Cloud systems automatically manage and optimize the use of resources by taking measurements at some level of abstraction corresponding to the type of service.

If the model (concept) of providing distributed and shared configurable computing resources corresponds to the above characteristics, then this is cloud computing.

Service cloud computing or cloud computing models:

Software as a Service ( SaaS ) - software as a service. In this model of providing cloud computing, the consumer uses provider applications running in the cloud infrastructure, which are accessible to the client through the interface (web browser) or the program interface. Consumers cannot manage and control the underlying cloud infrastructure, including the network, servers, operating systems, data warehouses, or even change the settings of a particular application.

Platform as a Service ( PaaS ) - platform as a service. The cloud computing model, in which the consumer gains access to the use of a software platform: operating systems, DBMS, application software, software development and testing tools. In fact, a consumer rents a computer platform with an installed operating system and specialized tools for developing, hosting and managing web applications. The consumer does not control the underlying cloud infrastructure, including the network, servers, operating systems, or data warehouses, but it manages the deployed applications and possibly environment configuration settings.

Infrastructure as a Service ( IaaS ) - infrastructure as a service. The model provides cloud computing, in which the consumer can manage processing and storage facilities, as well as other fundamental computing resources (virtual servers and network infrastructure), on which he can independently install operating systems and application programs for his own purposes. In essence, the consumer leases abstract computing power (server time, disk space and bandwidth of network channels) or uses the services of IT infrastructure outsourcing. The consumer does not manage the core cloud infrastructure, but manages the operating systems, storage, and applications deployed by it.

Cloud computing deployment models, i.e. cloud computing:

Private cloud (private cloud) - the infrastructure intended for use of cloud computing in the scale of one organization.

A community cloud is a cloud infrastructure that is intended for the exclusive use of cloud computing by a particular community of organizations from organizations that solve common problems.

Public cloud (public cloud) - an infrastructure designed for the free use of cloud computing by the general public.

Hybrid cloud is a combination of various cloud infrastructures (private, public or communities) that remain unique objects but interconnected by standardized or private technologies that provide the ability to exchange data and applications.

The merits of cloud computing 

accessibility - clouds are accessible to everyone, from anywhere where there is Internet, from any computer where there is a browser. This allows users (enterprises) to save on the purchase of high-performance, expensive computers. Also, employees of companies are becoming more mobile as they can access their workplace from anywhere in the world using a laptop, netbook, tablet or smartphone. There is no need to purchase licensed software, its settings and updates, you just go to the service and use its services paying for actual use.

low cost - the main factors that reduce the cost of using clouds are the following:

- reducing the cost of servicing the virtual infrastructure caused by the development of virtualization technologies, due to which less staff is required to service the entire IT infrastructure of the enterprise; 

- payment of the actual use of resources, the cloud user pays for the actual use of the computing power of the cloud, which allows him to efficiently distribute his money. This allows users (enterprises) to save on the purchase of licenses to software;

- the use of a cloud on a leasehold basis allows users to reduce the cost of purchasing expensive equipment, and focus on investing money in setting up business processes of an enterprise, which in turn makes it easy to start a business;

- the development of the hardware of computing systems, and therefore the reduction in the cost of equipment. 

flexibility - unlimited computing resources (memory, processor, disks), through the use of virtualization systems, the process of scaling and administering the "clouds" becomes quite an easy task, because the "cloud" alone can provide you with the resources you need, and you only pay for their actual use. 

reliability - the reliability of “clouds”, especially located in specially equipped data centers, is very high, as such data centers have backup power sources, security, professional workers, regular data backup, high bandwidth of the Internet channel, high resistance to DDOS attacks.

Security - “cloud” services have a sufficiently high security with proper security, however, with a negligent attitude, the effect may be completely opposite.

Large computational power - you as a user of a “cloud” system can use all of its computational capabilities, paying only for the actual time of use. Enterprises can use this feature to analyze large amounts of data.