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Cloudy Times

Various categories of cloud services exist. This column brings light into the darkness…

Cloud computing is known as the next big thing in IT. But what is it exactly? In a cloud, the key players are the user and provider. Users have access to the cloud resources in form of (web) services, containing the functionality of software (inside the browser), platforms or infrastructures. Let’s see what’s behind it…

Infrastructure as a Service (IaaS): Here, the users can run virtual instances of servers without the need to directly access the bare metal. The users have administrator privileges inside their instances and can define the firewall rules at will. The number and type of supported operating systems inside an IaaS depends on the provider. IaaS allows the transfer of complete data centres into the cloud. The most popular IaaS around is the Amazon Elastic Compute Cloud (EC2). Some competitors are GoGrid, Joyent, FlexiScale and Rackspace Cloud. You want an IaaS at home? Try Eucalyptus. It has the same functionality as the popular Amazon cloud services EC2, S3 and EBS. All you need is one or more Linux machines with Xen or KVM.

Platform as a Service (PaaS). A PaaS is a scalable, integrated application runtime (and in many cases) development platform. Most providers support one or two programming languages. The target audience is developers. PaaS takes the level of abstraction further and has less flexibility in contrast to IaaS. But while using a PaaS, you have no administration overheads. Popular PaaS offerings are Google App Engine, Amazon Simple DB, Bungee Connect, Zoho Creator and the Windows Azure Services Platform. Running your own PaaS is possible with AppScale (same functionality than Google App Engine) and 10gen.

Software as a Service (SaaS). Enterprise-quality software (complete applications) is run by a provider and can be consumed as a utility by the users. No software has to be installed locally by the users – just a browser is needed. This advantage includes the main drawback: the user has to trust the provider regarding service availability and privacy issues, because not only the application itself but also the user’s data is stored by the provider. Popular SaaS offerings are Google Docs,, Gliffy, Clarizen, Zoho, SlideRocket, Adobe Photoshop Express and Apple For running a private SaaS, Sugar and Zimbra are two of the candidates available.

Humans as a Service (HuaaS). Following the principle of crowdsourcing, the human resource can be used for a few pence or for free. Wherever a computer is not very well suited to the task, and time and money is a problem, crowdsourcing can be the solution. The most popular marketplace for HuaaS is the Amazon Mechanical Turk. Remember The Guardian investigating your MPs’ expenses in 2009? This was crowdsourcing/HuaaS too.

These four categories of cloud systems show that there are many different technologies behind the cloud, but all of them use virtualisations and web services and have the potential to radically change IT as we know it.

Christian Baun has been involved in Linux/UNIX and open source since 1994, when he did his first Slackware 2.0 installation

This article originally appeared in issue 84 of Linux User & Developer magazine.

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