A private cloud is a cloud computing infrastructure created by an organization for its own internal use, rather than using someone else’s infrastructure (e.g., Amazon EC2).
The main thing that sets a private cloud apart from a commercially-used public cloud is where the hardware is kept and how it’s maintained.
A private cloud is typically hosted on the company’s own servers, within their own network infrastructure.
The main advantage one has with a privately-managed cloud is direct control over every aspect of the cloud’s implementation: the hardware, the networking, the operating system and other software used to create the cloud itself; the way security is implemented; even the APIs used (that is, if you’re using an open source system).
Another advantage of a private cloud is that it can generally be built from reasonably current commodity hardware.
The most stringent requirements, apart from disk space and memory, are processors that support virtualization — e.g., the Intel VT-x or AMD’s AMD-V extensions.
Most server-grade hardware, and even a fair amount of desktop-grade hardware, sold in the last few years will sport such features.
If the hardware is available and isn’t provisioned for anything — or is being de-provisioned from other things — it can be put to use as part of a cloud.
A third advantage is locality. A cloud hosted in your own datacenter, or on your own property, is far easier to move data into (and out of) than a cloud hosting elsewhere.
If you have the servers on another floor and want to use a 30GB disk image as part of your cloud setup, it’s easy enough to just walk over there and add the disk to the cloud.
A fourth advantage is security — that is, up to a point. If you are hosting your own cloud infrastructure on a private LAN, with no connections to the outside world, it’s theoretically a good deal easier to secure.
Since it’s your network and your boxes, you can exercise that much more discretion over it. That said, this presumes you have good security protocols in place to begin with:
One major disadvantage of a private cloud is the work involved in creating and maintaining the cloud.
The whole point of using someone else’s cloud infrastructure is to save you the trouble of having to build it yourself, since the work involved — especially for a cloud of significant size — is not trivial.
It becomes all the more difficult if you want to securely access the cloud from outside your corporate LAN
It’s doubly hard if you have no experience setting up such things, and need to figure it out as you go.
If that’s the case, you are better off not using such a cloud in a production environment — at least not until you’ve conquered the finer points of such a setup.
Virtual Private Cloud
If the prospect of setting up a private cloud seems daunting, a good intermediate step might be to create a virtual private cloud.
This is a portion of a public cloud infrastructure that has been set aside for use by an organization, and is only accessible via an IPsec virtual private network connection.
One example of VPC technology is Amazon’s Virtual Private Cloud. It’s currently in beta-test, but it’s reasonable to assume it will take on the same de facto standard quality as EC2 itself once it’s finalized.
Among its features: the administrator can assign ranges of private addresses within the cloud (virtual subnets) and, if you choose, have all data from that cloud routed through your own private security infrastructure before being sent to the Internet at large.
Another example that spans both public and private clouds is BlueLock’s BlueLock Box, a hardware device that works as a miniature cloud server but is managed by BlueLock’s support team and can also connect to BlueLock’s own cloud infrastructure for adding capacity or backup/restore functionality.
A major vendor of technology for creating private clouds is Eucalyptus, now offering version 1.6.2 of their software.
Eucalyptus interfaces directly with Amazon EC2, and in fact uses the same interface as EC2.
One touted advantage of Eucalyptus is how the interface module can be swapped with something else, should future developments in cloud technology yield up an interface as broadly used as EC2. But for now, EC2 is the default choice due to its wide adoption.
Eucalyptus has also been adopted as the cloud computing infrastructure for Ubuntu Server (which also works with EC2).
Another private-cloud company is Elastra, whose Enterprise Cloud Server was designed to make it easier to package and deploy application stacks into the cloud.
Elastra provides packaging support for Oracle’s database and WebLogic app servers, among many others. Amazon EC2 is of course supported, along with Microsoft’s Azure.
No mention of virtualization in any form would be complete without some discussion of VMware.
Their own private-cloud architecture is built on top of VMware vSphere, and they also offer an “infrastructre-as-a-service” version via vCloud Express. (The aforementioned BlueLock is one of VMware’s service partners for vCloud.)
Microsoft came late to virtualization and have likewise come late to cloud computing, but are preparing their own private cloud offerings (“Azure”) for later this year.
As you might expect, it’ll be built on top of Windows Server / Hyper-V, and will be managed with the forthcoming Dynamic Infrastructure Toolkit for System Center.