Anatomy of an Open Source Cloud: Infrastructure as a Service

Cloud computing is no longer a technology on the cusp of breaking outbut a valuable and important technology that is fundamentally changingthe way we use and develop applications. Volumes could be written aboutthe leadership role that open source is playing in the cloud andvirtualization domain, but this article provided a short introductionto some of the popular and visible solutions available today. Whetheryou're looking to build a cloud based on your own requirements fromindividual pieces or simply want a cohesive solution that works out ofthe box, open source has you covered.
This article begins with an exploration of the core abstractions ofcloud architectures (from Infrastructure as a Service IaaS), thenmoves beyond the building blocks to the more highly integratedsolutions. Although not a requirement, virtualization provides uniquebenefits for building dynamically scalable architectures. In additionto scalability, virtualization introduces the ability to migrate virtualmachines (VMs) between physical servers for the purposes of loadbalancing. The virtualization component is provided by a layer ofsoftware called a hypervisor (sometimes called a virtual machinemonitor - VMM). This layer provides the ability to execute multipleoperating systems (and their applications) simultaneously on a singlephysical machine. On the hypervisor is an object called a virtual machinethat encapsulates the operating system, applications, and configuration.Optionally, device emulation can be provided in the hypervisor or as aVM. Finally, given the new dynamic nature of virtualization and the newcapabilities it provides, new management schemes are needed. Thismanagement is best done in layers, considering local management at theserver, as well as higher-level infrastructure management, providingthe overall orchestration of the virtual environment.
As VMs are an aggregation of operating system, root file system, andconfiguration, the space is ripe for tool development. But to realizethe full potential of VMs and tools, there must be a portable way toassemble them. The current approach, called the Open VirtualizationFormat (OVF) is a VM construction that is flexible, efficient, andportable. OVF wraps a virtual disk image in an XML wrapper that definesthe configuration of the VM, including networking configuration,processor and memory requirements, and a variety of extensible metadatato further define the image and its platform needs. The key capabilityprovided by OVF is the portability to distribute VMs in ahypervisor-agnostic manner..."