When we talk about images in the Rackspace Cloud, what we are really referring to is an image record with which the image data file is associated.
An image data file can be a virtual hard disk (VHD).
An image record consists of a set of image properties (also known as image metadata) that describes the image.
Image properties have several functions:
They are used by the image owner to catalog the image. For example, public images provided by Rackspace have the
com.rackspace\_\_1\_\_release\_idproperty, which you can use to locate all available versions of a particular image. For images that you own, you can add your own cataloging properties so that you can efficiently search through your set of images.
They are used by the Cloud Servers API to determine whether a request to boot a server from a particular combination of image and flavor makes sense. For example, if the
min\_ramproperty of an image has a value of 512, then the specified flavor must provide at least 512 MB of RAM or the boot request is rejected.
They are used by the Cloud Servers scheduler to locate a host for a server. For example, the
hypervisor\_version\_requiresproperty specifies what version of XenServer the image expects to find when it is booted.
They are used by the hypervisor during the process of booting a server from an image. For example, the
auto\_disk\_configproperty indicates whether the hypervisor should expand the disk partition and file system found on the image to fit the server’s system disk.
They are used by Cloud Images in its handling of images. For example, if the
visibilityproperty indicates that an image is public, the image is included in each user’s image list.
A set of image properties is maintained by Cloud Images itself. Users (and in some cases, even system administrators) cannot modify these properties. Among these properties are:
checksum: The MD5 sum of the image data file
status: The current state of the image. An image must be in
activestatus to be used to boot a server.
owner: Indicates who owns the image
id: A universally unique identifier (UUID) assigned to this image