An introduction to web applications architecture
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# Infrastructure as a Service (IaaS)

NIST (2011) defines IaaS as:

> The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, and deployed applications; and possibly limited control of select networking components (e.g. host firewalls).

IaaS delivers a cloud computing infrastructure – servers, storage, network services and virtual machines – as services. Rather than purchasing these infrastructure components, clients instead purchase access to these components as services.

Using IaaS is particularly suitable for situations including:

- new organisations without the capital to invest in hardware
- organisations that are growing rapidly but purchasing additional hardware would be prohibitive
- speculative development of new lines of business without the need to invest in infrastructure components.

Examples of IaaS providers include Amazon Elastic Compute Cloud (EC2) and Google Compute Engine.

Amazon Elastic Compute Cloud (EC2) forms a central part of Amazon’s cloud-computing platform, Amazon Web Services (AWS), which supports both Amazon’s retail services and cloud services.

Google Compute Engine is the IaaS component of Google Cloud Platform which is built on the global infrastructure that runs Google’s search engine, Gmail, YouTube and other services.

We have seen that cloud computing provides three service models: laaS as the underlying infrastructure; PaaS as a web application development environment; and SaaS which replaces stand-alone applications with web applications. These three service models are key to understanding how the cloud has evolved, so it is important that you appreciate the key differences between them.

Cloud computing brings with it a number of key benefits, as well as risks, that should be carefully examined by any organisation looking to move to cloud computing. It is important for organisations to understand the different aspects of cloud computing and to assess their own requirements before deciding which service models are appropriate for their unique needs. Cloud computing is a rapidly accelerating revolution within IT and is likely to become the default method of IT service delivery in the future.

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OpenLearn - An introduction to web applications architecture
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