Cloud computing refers to both a subset of applications delivered as services over the Internet and the underlying hardware and software systems in the datacenters that provide those services. Cloud computing is usually divided into Infrastructure as a Service (IaaS), Platform as a Service (PaaS), and Software as a Service (SaaS), as shown in Figure below.
Figure Cloud computing service models
Each cloud service model provides a level of abstraction that reduces the efforts required by the service consumer to build and deploy systems. In a traditional on-premises data center, the IT team has to build and manage everything. Whether the team is building proprietary solutions from scratch or purchasing commercial software products, they have to install and manage one-to-many servers, develop and install the software, ensure that the proper levels of security are applied, apply patches routinely (operating system, firmware, application, database, and so on), and much more. Each cloud service model provides levels of abstraction and automation for these tasks, thus providing more agility to the cloud service consumers so they can focus more time on their business problems and less time on managing infrastructure.
a. Infrastructure as service (IaaS)
The customer's ability to deliver computing, storage, networking, and other primary computer services through which the consumer can install and manage virtual machines, including operating systems and applications. The user does not handle the cloud infrastructure but may have control over operating systems, storage, and apps, and may have little control over selected networking components. Example: Amazon (EC2) delivers physical and virtual services to customers includes consumer specifications, memory, OS, and storage. As a service provider, IaaS provides the virtual server with one or more central operating units running different options (IaaS), a centralized, fully automated package, which owns and hosts a service provider and provides customers with computing services accompanied by storage and networking facilities on request. Characteristics of IaaS are:
(i) infrastructure services are distributed
(ii) dynamics are permitted
(iii) has a variable cost
(iv) model price of utility
(v) self-service and auto-supply
(vi) requires multiple users in a resource pool
b. Platform as Service (PaaS)
It provides an acceptable framework or medium for the developer to build applications and programs and distribute them on the network without getting the production environment installed or managed. To run available software or to build and test the latest, PaaS allows clients to rent software-defined servers and attached resources. The client is not in charge of the hardware of the cloud, such as servers, networks, storage, and OS. However, the client controls the applications and their configuration. Google application engine and Microsoft Azure are the most recent examples of PaaS. It is focused on the creation and usage of cloud software by deployers and developers. The multi-layer architecture is highly scalable, e.g. Salesforces.com and Azure. This model uses tools and/or libraries that act as the framework. Characteristicsof PaaS:
(i) architecture for multi-tenants
(ii) security/sharing granular access (permissions model)
(iii) motor/capacity robust workflow and built-in device scalability
(iv) including load and failover balancing
(v) user Interface Customizable/Programmable
(vi) Customization of limitless database
(vii) scalable integration platform "services-enabled."
(viii) self-service and auto-supply
c. Software as a service (SaaS)
The opportunity to use apps of the provider that operate on a cloud platform provided to the consumer. Applications can be accessed by a web application interface, such as a web browser (e.g. a web-based email) or the application interface, from separate client devices. With the potential exception of a small range of device setups for consumers, the customer does not handle or monitor the cloud infrastructure, including the network, servers, operating systems, storage, or even specific applications. SaaS primarily focuses on the end-user interface, as end users can use and manage this cloud-built software. Examples of SaaS are CRM, Google apps, Deskaway, and Wipro w-SaaS. Characteristics of SaaS are:
(i) applications that are open to consumers at any time,
(ii) SaaS suppliers do not have their applications hosted in the client's premises, but host software themselves to third parties,
(iii) the programs are then accessible by a web interface, which delivers the functionality and related data from virtually any point where an internet connection is accessible, This arrangement also enables several users to be flexible, It still places some customer discretion in the hands of the customer, For example, they can split the application with their clients and spend much better on them, and The SaaS model also helps users to accept both app upgrades and repairs simultaneously easily.
Cloud computing delivers promising customer capabilities. Consumers can use these services on request at any expense. SaaS helps the user run a software program on the Internet without installing it on its device, thereby simplifying everything and reducing maintenance costs. PaaS offerson-demand platforms that provide a computer interface and solution stack as a customer service. The infrastructure provider supplies software engineers with tools and libraries, hosting, servers, databases, storage, networks, user interactions, and frameworks. IaaS offers organizations leased facilities relating to servers, computers, network equipment, hardware, and applications. These cloud platforms are thought to be commonly adopted by enterprise organizations to fulfil their IT requirements soon as well as to redefine new cloud computing principles and protocols.
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