There has always been a lot of confusion around the exact meanings of the various cloud service models and their intersection with deployment strategies. That's hardly surprising given that IaaS, PaaS, SaaS, public cloud, private cloud, hybrid cloud, and a dozen other as-a-service modalities are a complex combination of marketing speak and technical jargon. In this article, I'd like to tease out one confused strand: the relationship between Infrastructure-as-a-Service and public or private cloud deployments. I've chosen to address this topic because there's often considerable confusion around what a private cloud is: I've heard people say that a private cloud can't involve virtualization, that its just another name for traditional in-house deployments, that it's a form of colocation, that Google Apps is a private cloud, and so on — none of which are remotely accurate or at least not completely so. A key distinction that causes some confusion is that IaaS platforms do not necessarily entail a public cloud, from which it follows that there is nothing contradictory about a private Infrastructure-as-a-Service platform. Let's start with some definitions.
Each of the main X-As-A-Service modalities specifies exactly what's being provided. IaaS provides clients with servers and networking hardware that they deploy on-demand. It almost always uses a hypervisor to virtualize hardware on top of physical servers. Clients are given access to infrastructure that is easy to deploy and easy to scale without the hassle of managing the underlying physical infrastructure.
The Public Cloud
Public cloud platforms like Cartika's Public IaaS solution are the prototypical cloud. When people say cloud, they usually have in mind the public cloud, with its on-demand infrastructure, scalability, and openness to everyone. The latter is the key feature of the public cloud: it is a shared platform. Multiple platform users will run workloads on the same physical hardware, although none will be aware of the other.
Private Infrastructure-as-a-Service platforms are substantially similar to public platforms, with the obvious difference being that only one client can run virtual infrastructure on the underlying physical hardware. The source of much of the confusion around private clouds is the assumption that the underlying hardware must be owned and managed by the organization that uses it. But, in reality, a hosting company like Cartika can provide private cloud hosting just as we can provide public hosting — the difference is in who has access to the underlying hardware, not in whose data center that hardware is kept. Image: Flickr/Marcin Wichary