The Xen Project is Built for Cloud Computing

Cambridge University started the Xenoservers project, aiming to develop public infrastructure for wide-area distributed computing, in the late 1990s. In 1999, The Cambridge team published a Hot Topics in Operating Systems paper that described Xenoservers as

A new distributed computing paradigm, termed global public computing, which allows any user to run any code anywhere. Such platforms price computing resources, and ultimately charge users for resources consumed.

The Xen Project Hypervisor was built by Cambridge University for the XenoServers project as a mechanism to divide up the physical resources among the cloud tenants and to provide resource management, accounting and auditing that was needed to run a cloud service. In other words, the hypervisor was built for the Cloud straight from the outset, anticipating a highly virtualized world, which today is known as cloud computing.

The Xen Project Software Facilitates Some of the Biggest Clouds in the World

Our hypervisor and supporting software has been used in Clouds ever since the Cloud came into existance.

In 2006, Amazon launched the Elastic Compute Cloud (EC2) and Slicehost launched their services. Both are based on our hypervisor.

Werner Vogels, CTO of Amazon said:

"Xen is great. It is powerful and easy to use. But most important is the very active community around it. That was a very big reason for us in selecting Xen. "

Since then, many Cloud Services (including Rackspace Cloud and Linode) and many Hosting Services have launched with our hypervisor as the hypervisor of choice.

In 2009, XCP, a binary distribution of the Xen Project Management API (or XAPI) , was announced and first released under open source licenses in early 2011. Xen Project integrations using XAPI for cloud orchestration stacks such as Eucalyptus, Apache CloudStack, OpenNebula and OpenStack followed. Later in 2011, Internap launched a public cloud service based on XAPI and Openstack: the first public cloud built on OpenStack. This was followed shortly by Rackspace who migrated their Xen Project-based cloud offering to XAPI and OpenStack. Early in 2012, XAPI packages were made available in Debian and Ubuntu Server, making it easier to build XAPI based clouds using Linux distributions. In June 2013, XenServer – a superset of XCP - was fully open sourced by Citrix and made available on

Just How Does the Xen Project Software Facilitate the Construction of Clouds?

Virtualization technology can be used either on its own or in the cloud. Our software is readily used in either situation. In order to facilitate its use in the cloud, we include the Xen Project API (XAPI).  This is the power behind cloud solutions like XenServer and the (now deprecated) XCP.

Support for Cloud Operating Systems

Xen Project has led the charge into the area of cloud operating systems. These lightweight, special-purpose operating systems are not meant to run on hardware. Rather, they are designed for producing small VMs which can populate massive clouds with minimal hardware. Our project produces Mirage OS, one of the first cloud operating systems to reach production-ready status. In addition, there are other cloud operating systems such as LING (formerly Erlang-on-Xen) and OSv which can populate a Xen Project-powered cloud.

XAPI, an API Which Enables Clouds

The Xen Project Management API (XAPI) is:

  • A Xen Project Toolstack that exposes the XAPI interface. When we refer to XAPI as a toolstack, we typically include all dependencies and components that are needed for XAPI to operate (e.g. xenopsd).
  • An interface for remotely configuring and controlling virtualised guests running on a Xen-enabled host. XAPI is the core component of XenServer.

XAPI adds additional functionality compared to other Xen Project toolstacks, including:

  • Extending the software to cover multiple hosts
  • Enhancing the VM lifecycle, including live snapshots, VM checkpointing, and VM migration
  • Enabling resource pools to include live migration, auto configuration, and disaster recovery
  • Allowing flexible storage and networking including integrated Open vSwitch support and storage XenMotion® live Migration (cross-pool migration, VDI migration)
  • Enabling event tracking, with progress and notification
  • Creating upgrade and patching capabilities
  • Facilitating real-time performance monitoring and alerting
  • Integrations with cloud orchestration stacks
  • Built-in support and templates for Windows and Linux guests

XAPI consolidates server workloads, enables savings in power, cooling, and management costs and thus contributing to environmentally sustainable computing, an increased ability to adapt to ever-changing IT environments, an optimized use of existing hardware, and an improved level of IT reliability. See success stories for detailed Xen Project user studies or our ecosystem directory for vendors, products, projects, services and research.

What was XCP?

XCP was a turnkey open source virtualization solution that provided out-of-the box virtualization and cloud computing. XCP included CentOS, the hypervisor, the enterprise ready Xen Project API toolstack, and integration with cloud, storage and networking solutions. In short, XCP was an open source binary distribution (ISO) of Xen Project software, XAPI and other components.

In June 2013, XenServer – a superset of XCP - was fully open sourced by XenServer and made available on This has removed the need to deliver newer versions of XCP via the Xen Project website. For more information see the FAQ.

Getting XAPI

XAPI comes in several variants:

  • XAPI is delivered as a source distribution by the XAPI project (see downloads). XAPI source releases are the basis for other XAPI deliverables.
  • XAPI toolstack packages in Linux (or XAPI packages) enable you to build an XenServer-like environment from packages that are distributed via your host operating system's package manager. XAPI packages are only available from supported Linux distributions (currently Debian and Ubuntu). Using XAPI packages provides more flexibility in tailoring your environment to your needs, but comes at the cost of less functionality and a more complex set-up. For more information see XAPI for Debian based distributions and XAPI variants. 
  • In June 2013, XenServer was fully open sourced, which means you can get an source distribution of XAPI from Note that this removed the need to deliver the XCP as a separate open source distribution on this website (also see FAQ).
  • Before June 2013, XenServer was not fully open sourced and a subset of XenServer called XCP was made available for download from this website. The Xen Project will continue to host these binaries, but new binaries will not be made available on this site (also see FAQ). This version of XCP installs onto your host from an ISO, providing a complete enterprise-ready out-of-the-box server virtualization and cloud computing platform after install.

XAPI Information

You can find more information about XAPI below: