VMware VCLOUD API 1.0 - TECHNICAL NOTE, Руководство по программированию

Страница: 204 / 212

vCloud API Programming Guide
204 VMware, Inc.
A virtual application or virtual machine is typically made up of one or more virtual disk files that contain the
operating system and applications that run on the virtual machine, and a configuration file containing
metadata that describe how the virtual machine is configured and deployed. An OVF package includes these
components, as well as optional certificate and manifest files. The package can be distributed and stored as a
collection of individual files, or as a single archive (OVA) file.
About OVF Packages
An OVF package includes four kinds of files:

An OVF descriptor, an XML file that contains metadata that describe a virtual machine or collection of
related virtual machines and the deployment environment they require. By convention, this file has the
suffix .ovf .

Virtual disk files. The descriptor lists these files and includes information about their format.

An optional certification file, which can be used to certify the authenticity of the package.

An optional manifest file, which contains a SHA ‐ 1 digest of each of the files in the package.
About OVA Files
An OVA file collects all the files in an OVF package into a single archive. By convention, this file has the
suffix .ova . This release of the vCloud API does not support upload or download of OVA files.
How the vCloud API Uses OVF
The vCloud API uses the OVF package as a unit of distribution and storage for vApp templates. Because these
artifacts are uploaded, downloaded, and stored in OVF package form, the vCloud API supports access to and
deployment of the widest possible variety of virtual applications. The vCloud API implements an instantiation
mechanism that transforms an OVF package into a vApp by binding the package’s abstract resource
requirements to specific resources in a deployment environment defined by a vDC.
Because of its generality, the OVF includes a great deal of information, nearly all of which is reused in VApp
elements. Some of this information is reused in unaltered form, with entire ovf:Section_Type elements
included in the VApp body. Other sections are transformed or extended by instantiation. While it is not
necessary for a user of the vCloud API to have a detailed knowledge of all the elements of an OVF package, a
basic understanding of a few key parts the package and how they relate to vApp templates and vApps can be
useful.
Virtual Machines
An OVF Envelope collects all of the metadata that describes a single virtual machine into a VirtualSystem
element. An Envelope that contains more than one VirtualSystem collects them into a
VirtualSystemCollection element. This arrangement supports packaging a group of related virtual
machines as a single object, and includes provisions for specifying global parameters such as virtual machine
startup order, network connections, and a range of resource configurations (such as processing power and
memory) to which the virtual machines can be deployed.
The vCloud API also supports this kind of packaging of multiple virtual machines. When you instantiate a
VAppTemplate , information from its VirtualSystem and VirtualSystemCollection elements is
propagated to the created VApp . VirtualSystem elements in a VirtualSystemCollection become Vm
elements contained by the Children element of a VApp .
For more information about instantiation, see “Instantiate a vApp Template” on page 61. For a detailed
example of an Envelope and its sections, see “Reconfiguring vApps and Virtual Machines” on page 69. For
more information about the purpose and contents of the OVF Sections included in a vApp or Vm , see “VApp”
on page 162.