Cloud Services

The three primary types of cloud computing are IaaS, PaaS and SaaS - infrastructure, platform and software as a service, respectively. When you take a closer look, user will see that what will decide this argument are your own company's needs and comfort level.

These services are made possible by virtualization, the ubiquity of high-speed networks and the capabilities of today's browsers. With these things in place, it becomes less necessary to own your own infrastructure or even to own your own software. You can get what you need from the cloud, as you need it.

SaaS is really geared toward the end users in your organization and does not take much to get started. The provider figures out how many resources to devote to your use of the application. The provider figures out the servers, the virtual machines, the network equipment, everything. You just point your browser at it.

In this model, cloud providers install and operate application software in the cloud and cloud users access the software from cloud clients. The cloud users do not manage the cloud infrastructure and platform on which the application is running. This eliminates the need to install and run the application on the cloud user's own computers simplifying maintenance and support. What makes a cloud application different from other applications is its elasticity. This can be achieved by cloning tasks onto multiple virtual machines at run-time to meet the changing work demand. Load balancers distribute the work over the set of virtual machines. This process is transparent to the cloud user who sees only a single access point. To accommodate a large number of cloud users, cloud applications can be multitenant, that is, any machine serves more than one cloud user organization. It is common to refer to special types of cloud based application software with a similar naming convention: desktop as a service, business process as a service, Test Environment as a Service, communication as a service. The pricing model for SaaS applications is typically a monthly or yearly flat fee per user.

PaaS is somewhere in between IaaS and SaaS. It is not a finished product, like SaaS and it is not a tabula rasa, like IaaS. PaaS gives your application developers hooks and tools to develop to that particular platform. For example, Microsoft's Windows Azure gives you tools to develop mobile apps, social apps, websites, games and more. You build these things, but you use the APIs and tools to hook them into the Azure environment and run them there.

In the PaaS model, cloud providers deliver a computing platform and/or solution stack typically including operating system, programming language execution environment, database and web server. Application developers can develop and run their software solutions on a cloud platform without the cost and complexity of buying and managing the underlying hardware and software layers. With some PaaS offers, the underlying compute and storage resources scale automatically to match application demand such that the cloud user does not have to allocate resources manually.

IaaS is at the other end of the cloud spectrum. In this scenario, you want to maintain control of your software environment, but you do not want to maintain any equipment. You do not want to have to buy servers and put them in a climate-controlled room or any of that. Instead, you go to an IaaS provider and request a virtual machine.

In this most basic cloud service model, cloud providers offer computers – as physical or more often as virtual machines, raw (block) storage, firewalls, load balancers and networks. IaaS providers supply these resources on demand from their large pools installed in data centers. Local area networks including IP addresses are part of the offer. For the wide area connectivity, the Internet can be used or - in carrier clouds - dedicated virtual private networks can be configured.

To deploy their applications, cloud users then install operating system images on the machines as well as their application software. In this model, it is the cloud user who is responsible for patching and maintaining the operating systems and application software. Cloud providers typically bill IaaS services on a utility computing basis, that is, cost will reflect the amount of resources allocated and consumed.