The term “cloud” is often misunderstood. Some think just because you may be outsourcing an Internet-accessible software application (email, FTP, etc.) to someone else, as opposed to installing licensed software on your own in-house server, that you are using “The Cloud”. Application outsourcing is called Software-as-a-Service (SaaS), but SaaS and “cloud” are not the same thing – even though many SaaS companies use a cloud as a delivery platform.
What is a Cloud?
In a nutshell, cloud computing is about one thing -- server virtualization. Virtualization software (a.k.a. “hypervisors”) separate each physical machine (“host”) into one or more virtual machines (“VM”s). Each VM consists of a virtual CPU, virtual memory, virtual storage and a “guest” operating system like Linux or Windows. To summarize,
A cloud server does the same thing as a traditional server, but it is virtual – not physical.
What is a Public Cloud?
You could say that Amazon Web Services (AWS) invented “The Cloud” in 2006 when they first released their Elastic Compute Cloud. AWS was originally targeted at testing and developing applications, as you could “spin up” a virtual server, assign it as many resources as needed (CPU, memory and storage); and you could shut it down and stop paying for it when you were done testing. As you can imagine, not having to invest capital in physical hardware is a great cost savings in development and testing environments.
So, AWS wasn’t originally targeted at production environments, but that has all changed as cloud adoption expanded. Microsoft followed AWS with its own public cloud called Azure. And, there are other cloud infrastructures such as OpenStack, originally a joint effort of Rackspace and NASA. AWS and others are each considered public clouds.
What is a Private Cloud?
A private cloud typically consists of either of the following scenarios:
- Two or more physical hosts dedicated to one company, with hypervisor technology so that company can create and manage its own virtual machines. This could be located in-house or could be co-located at a data center.
- A private pool of resources on a multi-tenant cloud. A private cloud within a multi-tenant cloud requires dedicated firewalls to create a Virtual Private Data Center (VPDC). Dedicated firewalls will handle both Internet networking and custom private networking for all VMs created from the resource pool. A VPDC is therefore completely isolated from the other cloud tenants, as well as being protected from the outside.