You’ve probably heard people use the terms private cloud, public cloud, and hybrid cloud. But how many really understand what they actually mean? These concepts are sometimes used incorrectly in everyday conversation, so we’re here to set the record straight based on the official definition of cloud put forth by the National Institute of Standards and Technology (yes the US government actually created a cloud computing definition).
Public Cloud vs Private Cloud Differences
Most conversations about “the cloud” refer to public clouds, where different organizations share cloud resources in a data center owned by a cloud provider such as Amazon, Microsoft, or Google. The big difference between public and private cloud is that a private cloud is used exclusively by a single organization, which most often means that the computing resources are located on-premises in the offices of that organization.
Most people understand that fundamental distinction between cloud types, but sometimes people butcher the term private cloud because they don’t understand the basic definition of cloud computing. To qualify as cloud computing, any cloud model (whether public, private, or hybrid) must first meet the 5 criteria of cloud computing: On-demand self-service, shared resource pooling, rapid elasticity, measured service, and broad network access. Just because you have several local computers in a server, it doesn’t mean you have a private cloud.
Why would you use a private cloud?
In larger corporations or public institutions with a lot of demand for computing power to run various services, it can be more cost effective to pool shared computer resources among various internal groups.
Additionally, a private cloud can be a good solution for organizations looking to get the benefits of cloud computing while maintaining control over data, as often sensitive information can’t be sent to a public cloud provider by law, for example with government agencies. Other organizations might be concerned with public cloud security. With private cloud, having computing resources internally is often more efficient than relying on an external public cloud provider because the data doesn’t have to travel far, for example across the Internet, which can lead to bottlenecks without a very fast (and often expensive) connection.
In a private cloud, usage of resources is measured and can scale depending on the changing needs of a department, just like in a public cloud. As a result, sometimes organizations even charge the internal departments using computing resources like a public cloud provider would. This internal billing for cloud resources is known as chargeback.
Because private clouds are inside of an organization’s data center, they typically have to be managed in-house. However, there are some vendors that offer managed private cloud services, where varying degrees of the operational and maintenance of your cloud infrastructure is handled by the cloud provider.
What is hybrid cloud?
Private vs public cloud is not always an either or situation… you can have the best of both worlds. Hybrid cloud is a model that describes when a public cloud is bound together with another cloud type (like a private cloud) and there is data or application portability between the two. So if you had two web servers in a server room at your office and another 2 web servers in Microsoft Azure and all 4 servers that could load balance between each other, that would represent a hybrid cloud model. Similarly, if you were able to migrate a virtual machine running on local cloud infrastructure to a Microsoft Azure Virtual Machine instance, that would represent a hybrid model as well.
To be clear, hybrid cloud doesn’t simply mean that you have some servers locally and some unrelated instances run by a cloud provider… the linkage and communication between them is key. Use cases for hybrid clouds include being able to scale resources rapidly to cloud infrastructure to meet increased computing demands or syncing data between two locations to ensure redundancy.
Community cloud: The little-known cloud model
Community cloud is a model that has two similar organizations with shared concerns using the same cloud computing resources. For example if there was a group of 3 hospitals in a geographically similar location, they could share community cloud resources with each other.
Community cloud falls in-between public and private cloud. The model is not open to use by the general public, but at the same time it’s not for the sole use of a single organization.