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,
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