Build your Private Cloud with Xen Cloud Platform

Sandeep Koul

Cloud computing has caught everyone's imagination, but the buzz is largely around using public cloud services. There's still a lot of fuzziness around building your own private cloud. Sure, the idea of having a repository of applications, storage or even computing power and the ability to ration these IT assets based on your requirement appeals to every CIO. Who wouldn't want a well-orchestrated IT infrastructure with fewer servers, automatic resource provisioning, and more savings. But there's a lot of confusion on how to go about doing the same. While you could go for a commercial private cloud computing solution, that would cost you. So here we talk about an open source private cloud computing solution, Xen Cloud Platform or XCP, for which all you need to invest is man-hours and of course the hardware. It's freely downloadable, and here we'll take you through step by step instructions on how to deploy it. You can either download it from http://www.xen.org/products/cloud _source.html, or simply take it from this month's PCQuest DVD.

XCP stack
As the name suggests, XCP is a virtualization platform for Cloud. It consolidates your hardware servers into a pool of resources comprising of CPUs, RAM, and, storage space. You could use a separate centralized storage space on a NAS or SAN as well for this, which would basically store all the virtual machines you create. At the heart of XCP lies the Xen Hypervisor, which was discussed in detail in the PCQuest Nov 2010 issue (find it here: http://bit.ly/9CmKtq). The other important components of XCP are the XAPI tool stack and prototype web UI.

The Hardware requirements

There is no special hardware requirement for XCP. In all probability, what you need for this would already be present in your setup. While choosing servers or a set of servers (hosts as we would call them from now onwards) for implementing XCP, one important point to keep in mind is family of processors on them. They all must contain the same family of processors, otherwise they can't be pooled together. This is due to the difference in instruction set. So if for instance, you have one host with an Intel processor and another with AMD, you cannot pool them together. Even having Xeon and Core 2 Duo based servers won't work. Also, just ensure that you have plenty of memory on these hosts because you'll be running multiple virtual machines on them. Make sure all your hosts are sitting in the same subnet, so that they can talk to one another. It would be good to put them on a Gbps network. Refer to the box on detailed hardware requirements to know exactly what you need to implement XCP.

Deployment scenarios

There are three common deployment scenarios for XCP. The simplest one is to have separate hosts with their own storage space and XCP running on them. This scenario, though the simplest, doesn't allow you to move VMs from one host to another. So essentially, you don't have a pool of resources that can be pulled in whenever needed.To overcome this, there are two other recommended scenarios. One other scenario is to have multiple hosts with a shared NFS storage, and the third one is to have a common, shared iSCSCI storage target. So if you have an IP SAN, then all your VMs could reside in that, and you can use XCP to assign CPU and RAM from a pool of guests to those VMs.
In the following pages we will show you how to successfully build a private cloud infrastructure using XCP hosts on a shared NFS storage.

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