(diagram from Wikipedia: Cloud Computing)
Since cloud computing is accessed as a service, most people are unaware of the vendors providing cloud solutions. The dominant cloud solution is Xen (see Xen in the Cloud), the open source virtualization software used by leading cloud providers like Amazon, Rackspace and GoGrid to deliver cloud services to their customers.
The Xen Cloud Platform (XCP) project offers a complete cloud platform based on Xen and other open source components in order to deliver a fully integrated stack, making it simpler for service providers and enterprises to deploy cloud computing solutions.
Enterprises evaluating cloud computing solutions should consider the benefits of using the same software stack as the public cloud providers. A common software stack eases integration between public and private cloud services and facilitates migration of services between hosted and internal virtual servers. This mobility is particularly attractive when using hosted facilities as a way to create an "elastic cloud", adding capacity from service providers to increase geographic coverage, provide off-site service redundancy, or to expand capacity during periods of high demand. A shared software stack provides seamless management of resources throughout the cloud infrastructure, simplifying management, reducing operating costs and improving agility.
The Xen/XCP stack includes the Open vSwitch, providing an open source alternative to proprietary virtual switches (such as Cisco Nexus 1000v and the VMware Distributed Switch).
A previous article, describes the visibility provided by sFlow monitoring built into the Open vSwitch. Implementation of the sFlow standard in the vSwitch extends the monitoring already available in most vendor's hardware switches into the virtualization layer, providing seamless visibility and control of all physical and virtual network resources in the cloud.
Many service providers already use sFlow-based billing solutions. The availability of sFlow in the Xen/XCP stack provides additional flexibility for usage based accounting and billing in virtual hosting and cloud service environments.
Finally, the detailed visibility that sFlow provides helps lower costs by optimizing resource utilization and reducing the need for over provisioning.
Feb. 15, 2011 Update: More recent articles describing sFlow configuration in XCP and other cloud platforms can be found by clicking on the vSwitch label below.