What is cloud computing?

Wikipedia defines cloud computing as:

"Cloud computing is internet-based computing in which large groups of remote servers are networked to allow the centralized data storage, and online access to computer services or resources."

The National Institute of Standards and Technology (NIST) gives the following definition of cloud computing:

"Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction."

There are several other broadly accepted definitions of cloud computing. Some explicitly emphasize configurability of the resources, while others include the need for rapid on-demand provisioning of resources, and still others drop the requirement of access via the internet. We define cloud computing as a model that enables the features listed here:

• Users should be able to provision and release resources on-demand
• The resources can be scaled up or down automatically, depending on the load
• The provisioned resources should be accessible over a network
• Cloud service providers should enable a pay-as-you-go model, where customers are charged based on the type and quantum of resources they consume

Some of the implications of choosing to use the cloud for your computing needs are as follows:

• The illusion of infinite processing and storage resources, available on-demand, reduces the need for detailed advance planning and procurement processes.
• The model promotes the use of resources as per customer needs, for example, starting small, and then increasing resources based on an increase in need.
• The development and test environments can be provisioned on a smaller scale than production environment, and enabled only during normal business hours, to reduce costs.
• The staging environment can be provisioned for a short duration to be a replica of the production environment. This enables testing using production configuration (and scale) for improved defect resolution.
• There will be ease of scaling, both vertically and horizontally, in order to better manage spikes in demand and variations due to business cycles or time-of-day reasons, and so on.
• This encourages experimentation, by trying out new ideas and software by quickly provisioning resources, rather than requisition for resources through time-consuming and cumbersome processes.

In addition, there are several key operational and maintenance-related implications, including no hardware maintenance or data center operations required, zero-downtime migrations and upgrades, ease of replacement of unhealthy machines, ease of implementation of high-availability and disaster recovery strategies, and many more.

These and other implications of using cloud services to design scalable, highly available, and secure applications are discussed in-depth in subsequent chapters.