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Using Glance Programmatically with Glance's Client

While it is perfectly acceptable to issue HTTP requests directly to Glance via its RESTful API, sometimes it is better to be able to access and modify image resources via a client class that removes some of the complexity and tedium of dealing with raw HTTP requests.

Glance includes a client class for just this purpose. You can retrieve metadata about an image, change metadata about an image, remove images, and of course retrieve an image itself via this client class.

Below are some examples of using Glance's Client class. We assume that there is a Glance server running at the address glance.example.com on port 9292.

Requesting a List of Public VM Images

We want to see a list of available virtual machine images that the Glance server knows about.

Using Glance's Client, we can do this using the following code

from glance.client import Client

c = Client("glance.example.com", 9292)

print c.get_images()

Requesting Detailed Metadata on Public VM Images

We want to see more detailed information on available virtual machine images that the Glance server knows about.

Using Glance's Client, we can do this using the following code

from glance.client import Client

c = Client("glance.example.com", 9292)

print c.get_images_detailed()

Filtering Images Returned via `get_images()` and `get_images_detailed()`

Both the get_images() and get_images_detailed() methods take query parameters that serve to filter the returned list of images.

When calling, simply pass an optional dictionary to the method containing the filters by which you wish to limit results, with the filter keys being one or more of the below:

name: NAME

Filters images having a name attribute matching NAME.
container_format: FORMAT

Filters images having a container_format attribute matching FORMAT

For more information, see About Disk and Container Formats <formats>
disk_format: FORMAT

Filters images having a disk_format attribute matching FORMAT

For more information, see About Disk and Container Formats <formats>
status: STATUS

Filters images having a status attribute matching STATUS

For more information, see About Image Statuses <statuses>
size_min: BYTES

Filters images having a size attribute greater than or equal to BYTES
size_max: BYTES

Filters images having a size attribute less than or equal to BYTES

Here's a quick example that will return all images less than or equal to 5G in size and in the saving status.

from glance.client import Client

c = Client("glance.example.com", 9292)

filters = {'status': 'saving', 'size_max': (5 * 1024 * 1024 * 1024)}
print c.get_images_detailed(filters)

Requesting Detailed Metadata on a Specific Image

We want to see detailed information for a specific virtual machine image that the Glance server knows about.

We have queried the Glance server for a list of public images and the data returned includes the uri field for each available image. This uri field value contains the exact location needed to get the metadata for a specific image.

Continuing the example from above, in order to get metadata about the first public image returned, we can use the following code

from glance.client import Client

c = Client("glance.example.com", 9292)

print c.get_image_meta("http://glance.example.com/images/1")

Retrieving a Virtual Machine Image

We want to retrieve that actual raw data for a specific virtual machine image that the Glance server knows about.

Continuing the example from above, in order to get both the metadata about the first public image returned and its image data, we can use the following code

from glance.client import Client

c = Client("glance.example.com", 9292)

meta, image_file = c.get_image("http://glance.example.com/images/1")

print meta

f = open('some_local_file', 'wb')
for chunk in image_file:
    f.write(chunk)
f.close()

Note

The return from Client.get_image() is a tuple of (metadata, file) where metadata is a mapping of metadata about the image and file is a generator that yields chunks of image data.

Adding a New Virtual Machine Image

We have created a new virtual machine image in some way (created a "golden image" or snapshotted/backed up an existing image) and we wish to do two things:

Store the disk image data in Glance
Store metadata about this image in Glance

We can do the above two activities in a single call to the Glance client. Assuming, like in the examples above, that a Glance API server is running at glance.example.com, we issue a call to glance.client.Client.add_image.

The method signature is as follows:

glance.client.Client.add_image(image_meta, image_data=None)

The image_meta argument is a mapping containing various image metadata. The image_data argument is the disk image data and is an optional argument.

The list of metadata that image_meta can contain are listed below.

name

This key/value is required. Its value should be the name of the image.

Note that the name of an image is not unique to a Glance node. It would be an unrealistic expectation of users to know all the unique names of all other user's images.
id

This key/value is optional.

When present, Glance will use the supplied identifier for the image. If the identifier already exists in that Glance node, then a glance.common.exception.Duplicate will be raised.

When this key/value is not present, Glance will generate an identifier for the image and return this identifier in the response (see below)
store

This key/value is optional. Valid values are one of file, s3 or swift

When present, Glance will attempt to store the disk image data in the backing store indicated by the value. If the Glance node does not support the backing store, Glance will raise a glance.common.exception.BadRequest

When not present, Glance will store the disk image data in the backing store that is marked default. See the configuration option default_store for more information.
type

This key/values is required. Valid values are one of kernel, machine, raw, or ramdisk.
size

This key/value is optional.

When present, Glance assumes that the expected size of the request body will be the value. If the length in bytes of the request body does not match the value, Glance will raise a glance.common.exception.BadRequest

When not present, Glance will calculate the image's size based on the size of the request body.
is_public

This key/value is optional.

When present, Glance converts the value to a boolean value, so "on, 1, true" are all true values. When true, the image is marked as a public image, meaning that any user may view its metadata and may read the disk image from Glance.

When not present, the image is assumed to be not public and specific to a user.
properties

This key/value is optional.

When present, the value is assumed to be a mapping of free-form key/value attributes to store with the image.

For example, if the following is the value of the properties key in the image_meta argument:
```
{'distro': 'Ubuntu 10.10'}
```
Then a key/value pair of "distro"/"Ubuntu 10.10" will be stored with the image in Glance.

There is no limit on the number of free-form key/value attributes that can be attached to the image with properties. However, keep in mind that there is a 8K limit on the size of all HTTP headers sent in a request and this number will effectively limit the number of image properties.

If the image_data argument is omitted, Glance will add the image_meta mapping to its registries and return the newly-registered image metadata, including the new image's identifier. The status of the image will be set to the value queued.

As a complete example, the following code would add a new machine image to Glance

from glance.client import Client

c = Client("glance.example.com", 9292)

meta = {'name': 'Ubuntu 10.10 5G',
        'type': 'machine',
        'is_public': True,
        'properties': {'distro': 'Ubuntu 10.10'}}

new_meta = c.add_image(meta, open('/path/to/image.tar.gz'))

print 'Stored image. Got identifier: %s' % new_meta['id']

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