Building an internal cloud is as easy as installing VMware, right?

That's what a lot of customers think, but in reality the virtualisation of servers is just one of many required steps for enterprises that want to build a cloud network.

Last year, Forrester Research asked enterprises in a survey how many of them had built an internal cloud, and about 5% said they had, according to analyst James Staten. But when asked to define the internal cloud, IT executives typically replied "my VMware environment," Staten says.

In reality, adoption of internal clouds as defined by Forrester is less than two percent of enterprises, and vendors are just beginning to provide the proper tools necessary to build them, he says.

"The big challenge we see is most enterprises are not organisationally ready to deploy an internal cloud," Staten says. "You have to be ready to share resources among business units. Most enterprises are not."

Additionally, customers need extensive experience with virtualisation and automation technologies, and must be comfortable with letting users provision their own services through a self-service portal.

Cloud networks deployed by an enterprise for its own users are often called "private clouds", but that phrase has been co-opted by a few vendors to describe certain forms of external hosting services. Therefore, Forrester and other analysts have decided to use the phrase "internal cloud" to describe cloud networks that exist entirely within a customer's own IT infrastructure.

In a report titled "Deliver Cloud Benefits Inside your Walls," Forrester's Staten writes: "Architecturally, an internal cloud isn't that different from a virtualized scale-out infrastructure in today's enterprise. Both are composed of a collection of x86 servers topped with either a grid engine or a virtual infrastructure based on hypervisors."

But internal clouds have several key elements that go beyond virtualised infrastructure. For example, an internal cloud lets developers deploy applications to the cloud via a self-service portal, without any involvement from a server administrator, Forrester says.

Additionally, internal clouds have an automated workload distribution engine (such as those found in grid networks) to determine the best placement of new workloads and optimise the pool of virtualised computing resources to make room for more applications.

Moreover, internal clouds are multi-tenant, sharing resources across business units and divisions within a company that may not share computing equipment today, Staten says. "To account for the use of the virtual pool, internal cloud infrastructures usually provide a method of metering and tracking resource use that feeds chargeback or direct billing for the resources consumed," he writes.

In her research, Yankee Group analyst Agatha Poon defines three key elements of an internal cloud: the network, process and corporate culture.

On the network front, reliability and security become more important than ever in a cloud environment because of the reliance on a consolidated pool of processing and storage, Poon says. In addition to strict access controls, the network must be robust enough to survive a performance hit that could be caused by virtualisation.

"Running virtual machines on a single server and accessing them via Gigabit Ethernet could overwhelm the network, leading to degraded performance," Poon writes in a report titled "Rebuilding Corporate Data Centers as Private Clouds." "The situation is exacerbated as enterprise users expect to access business applications anywhere, anytime, resulting in applications being dynamically rerouted on the fly to meet specific requests."