What is cloud computing?

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

There are several other broadly accepted definitions of cloud computing. Some explicitly emphasize reconfigurability 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:

1. Users should be able to provision and release resources on-demand
2. The resources can be scaled up or down automatically, depending on the load
3. The provisioned resources should be accessible over a network
4. 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:

1. The illusion of infinite processing and storage resources, available on-demand, reduces the need for detailed advance planning and procurement processes.
2. 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.
3. The development and test environments can be provisioned on a smaller scale than the production environment, and enabled only during normal business hours, to reduce costs.
4. 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.
5. 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.
6. 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 centre 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.

Public, private, and hybrid clouds

Basically, there are three types of clouds in cloud computing, they are public, private, and hybrid clouds.

In a public cloud, third-party service providers make resources and services available to their customers via the internet. The customers’ applications and data are deployed on infrastructure owned and secured by the service provider.

A private cloud provides many of the same benefits of a public cloud but the services and data are managed by the organization or a third-party, solely for the customer’s organization. Usually, private cloud places increase administrative overheads on the customer but give greater control over the infrastructure and reduce security-related concerns. The infrastructure may be located on or off the organization’s premises.

A hybrid cloud is a combination of both a private and a public cloud. The decision on what runs on the private versus the public cloud is usually based on several factors, including business criticality of the application, the sensitivity of the data, industry certifications and standards required, regulations, and many more. But in some cases, spikes in demand for resources are also handled in the public cloud.

Cloud service models — IaaS, PaaS, and SaaS

There are three cloud-based service models, IaaS, PaaS, and SaaS. The main features of each of these are listed here:

1. Infrastructure as a Service (IaaS) provides users with the capability to provision processing, storage, and network resources on demand. The customers deploy and run their own applications on these resources. Using this service model is closest to the traditional on-premise models and the virtual server provisioning models (typically offered by AWS Online Training). The onus of administering these resources rests largely with the customer
2. In Platform as a Service(PaaS), the service provider makes certain core components, such as databases, queues, workflow engines, e-mails, and so on, which are available as services to the customer. The customer then leverages these components for building their own applications. The service provider ensures high service levels and is responsible for scalability, high-availability, and so on for these components. This allows customers to focus a lot more on their application’s functionality. However, this model also leads to application-level dependency on the providers’ services.
3. In the Software as a Service(SaaS) model, typically, third-party providers using a subscription model provide end-user applications to their customers. The customers might have some administrative capability at the application level, for example, to create and manage their users. Such applications also provide some degree of customizability, for example, the customers can use their own corporate logos, colours, and many more. Applications that have a very wide user base most often operate in a self-service model. In contrast, the provider provisions the application for the customer for more specialized applications. The provider also hands over certain application administrative tasks to the customer’s application administrator (in most cases, this is limited to creating new users, managing passwords, and so on through well-defined application interfaces).

From an infrastructure perspective, the customer does not manage or control the underlying cloud infrastructure in all three service models.

The following diagram illustrates who is responsible for managing the various components of a typical user application across IaaS, PaaS, and SaaS cloud service models. The column labelled User Application represents the main components of a user application stack, while the following columns depict the varying levels of management responsibilities in each of the three service models. The shaded boxes are managed by the service provider, while the unshaded boxes are managed by the user.

The level of control over operating systems, storage, applications, and certain network components (for example, load balancers) is the highest in the IaaS model, while the least (or none) in the SaaS model. We would like to conclude our introduction to cloud computing by getting you started on AWS, right away.

Summary

In this article, we introduced you to a few cloud computing concepts and terminologies. We described the basic features of public, private, and hybrid clouds. We introduced the main cloud delivery models, namely, IaaS, PaaS, and SaaS.