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<h1>Architecture</h1>
<p>Libvirt is a C toolkit to interact with the virtualization capabilities of
recent versions of Linux (and other OSes), but libvirt won't try to provide
all possible interfaces for interacting with the virtualization features.</p>
<p>To avoid ambiguity about the terms used here here are the definitions for
some of the specific concepts used in libvirt documentation:</p>
<ul><li>a <strong>node</strong> is a single physical machine</li><li>an <strong>hypervisor</strong> is a layer of software allowing to
virtualize a node in a set of virtual machines with possibly different
configurations than the node itself</li><li>a <strong>domain</strong> is an instance of an operating system running
on a virtualized machine provided by the hypervisor</li></ul>
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<img alt="Hypervisor and domains running on a node" src="node.gif" /></p>
<p>Now we can define the goal of libvirt: to provide the lowest possible
generic and stable layer to manage domains on a node.</p>
<p>This implies the following:</p>
<ul><li>the API should not be targeted to a single virtualization environment
though Xen is the current default, which also means that some very
specific capabilities which are not generic enough may not be provided as
libvirt APIs</li><li>the API should allow to do efficiently and cleanly all the operations
needed to manage domains on a node</li><li>the API will not try to provide high level multi-nodes management
features like load balancing, though they could be implemented on top of
libvirt</li><li>stability of the API is a big concern, libvirt should isolate
applications from the frequent changes expected at the lower level of the
virtualization framework</li></ul>
<p>So libvirt should be a building block for higher level management tools
and for applications focusing on virtualization of a single node (the only
exception being domain migration between node capabilities which may need to
be added at the libvirt level). Where possible libvirt should be extendable
to be able to provide the same API for remote nodes, however this is not the
case at the moment, the code currently handle only local node accesses
(extension for remote access support is being worked on, see <a href="bugs.html">the mailing list</a> discussions about it).</p>
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