Cloud Computing is an often cited and very confusing term in the market today. To try and clear things up a bit, I'm going to try and define and explain Cloud Computing from several angles. To do this, first I will define Cloud Computing. Cloud Computing is defined as the use of compute resources that are dynamically made available based on a request for a service provided by that cloud. This is similar to the definition that wikipedia provides. Breaking this definition down to a few core phrases should make things easier to understand. First, Compute Resources are the elements used to provide the service. Examples of Compute Resources are CPU, Memory, Disk, Network, all of which are often supplied through a virtual machine or some type of abstracted compute fabric (think a custom grid like Google). Next, we define Dynamic, meaning changing. In this case the change is driven by a request for some type of service. This service is provided by the Cloud and comes in several flavors including Infrastructure (IaaS) , Platform (PaaS) , and Software (SaaS). Why the word Cloud? Cloud originated as a way of describing something that was overly complex and should just be looked at as a "black box". The term was frequently used in the Telecom Industry and then was adopted by Networking (Specifically WANs - Wide Area Networks). WANs leverage the Telecom Industry Platforms, so hence the connection.
Compute Resources
Above is a Diagram of the core pieces that make up Resources in the Cloud. Note: I did not say Compute Resources, however everything in the stack ultimately relies on Compute Resources.
The use of these Compute Resources is where the magic happens. Different combinations of these resources make up the three types of Cloud offerings available today. They are:
- SaaS - Software as a Service
- PaaS - Platform as a Service
- IaaS - Infrastructure as a Service
Below we will cover a bit of detail on each of these. The architectures are not important right now, simply the concepts should be focused on.
Software as a Service (SaaS)
Software as a Service goes back to 1998/1999 when there were ASPs (no not Active Server Pages or Average Selling Prices) - Application Service Providers. ASPs provided applications to customers by leveraging remote display technologies such as Citrix. This was later superceded by Web based solutions, the most well know and successful being Salesforce.com . SaaS normally offers a multi-tenant based solution where users login and work with the application being provided. SaaS is either free or offered on a subscription basis (Monthly or Yearly are common).
Platform as a Service (PaaS)
Platform as a Service is based on leveraging APIs to write an Application without the need to create or manage the resources beneath it. In some cases SaaS vendors allow developers to create new applications that leverage their underlying platform APIs.
Infrastructure as a Service (IaaS)
Infrastructure as a Service provides the raw compute resources and allows the user (the developer or administrator) to decide what should be layered on top. This originates from the classic hosting world and allows the greatest flexibility, however it is also the most complex to manage from the user of the service (user being the developer or administrator).
A View of the XaaS Stack
It is important to note that this is not a comprehensive list of players in these different layers, this is simply a snapshot of some of the major market players in these areas.
Resource Links:
SaaS
PaaS
IaaS
Amazon,
Cloud,
Cloud Computing,
Gigaspaces,
Google,
IaaS,
Microsoft,
Netsuite,
PaaS,
Rackspace,
Rightscale,
SaaS,
Salesforce.com,
VMware,
XaaS