What is a Cloud?

The term “Cloud Computing” gets thrown around a lot these days, and while it does solve a lot of interesting problems, there is also a lot of confusion on what it really is, and I have not seen an easy to read, high level overview.

So, What is a Cloud?

While this seems like a simple question, usually its not easy to answer. This is because CLOUD means different things to different people, and it solves different problems for different customers. However, in its simplest form, a CLOUD is really just computing delivered as a service. Whether its Infrastructure as a Service (IAAS) like Amazon EC2, Platform as as Service (PAAS) like Google app engine, or Software as a Service (SAAS) like SalesForce.com;  all the end user cares about is, I need a resource to run a workload and I don’t care how or what happens under the covers, as long as I get the results I need.

There are other common characteristic of cloud computing. According to “cloud for dummies” [1], these include: Elasticity and the ability to scale up and down, Self-service provisioning and automatic deprovisioning, Standard(s) application programming interfaces (APIs) for building services, and billing and metering of service usage in a pay-as-you-go model.

The Federal Government also has similar “Essential Characteristics” for cloud commuting which you can see below[2]. While not all “clouds” have to exhibit all of these characteristics this helps give an idea of what computing as a serves is all about.

Private vs. Public?

Clouds are typicality categorized as either public or private clouds. This just determines where the cloud “lives” and who can access it. Private clouds typically reside inside a companies firewall and are usually only accessible by the employees of that company, where Public clouds live outside the firewall and usually can be accessed by anyone. Also private clouds are usually maintained internally, where companies have more control over their private cloud infrastructure. On the other hand, Public clouds are usually maintained by a third party, and companies have less control. Amazon EC2 is the largest/most prevalent public cloud. When people talk about public clouds they are more than likely talking about Amazon EC2.

What is a Hybrid Cloud?

A hybrid cloud is simply a cloud that is made up of both private and public resources. One of the most compelling use-cases of a Hybrid Cloud is burst capability. Where under normal operating conditions your workload is run internal on your resources in your private cloud, however under extreme load or critical situations you can burst out to the public cloud and consume additional resources as needed.

What is an Open Hybrid Cloud?

The concept of Open Hybrid Cloud simply means you have a hybrid cloud build off of open solutions and standards so you are not locked in to a single vendor or technology. One of the key features of an Open Hybrid Cloud is that you can easily move workloads to different technologies without having to re-architect your solution.

[1] http://www.dummies.com/how-to/content/what-is-cloud-computing.html
[2] http://csrc.nist.gov/publications/nistpubs/800-145/SP800-145.pdf

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