Using OpenStack Image

this page last updated: 2019-02-25 15:53:00

Using OpenStack Image¶

Before working with the Image service, you’ll need to create a connection to your OpenStack cloud by following the Connect user guide. This will provide you with the conn variable used in the examples below.

The primary resource of the Image service is the image.

List Images¶

An image is a collection of files for a specific operating system that you use to create or rebuild a server. OpenStack provides pre-built images. You can also create custom images, or snapshots, from servers that you have launched. Images come in different formats and are sometimes called virtual machine images.

def list_images(conn):
    print("List Images:")

    for image in conn.image.images():
        print(image)

Full example: image resource list

Create Image¶

Create an image by uploading its data and setting its attributes.

def upload_image(conn):
    print("Upload Image:")

    # Load fake image data for the example.
    data = 'This is fake image data.'

    # Build the image attributes and upload the image.
    image_attrs = {
        'name': EXAMPLE_IMAGE_NAME,
        'data': data,
        'disk_format': 'raw',
        'container_format': 'bare',
        'visibility': 'public',
    }
    conn.image.upload_image(**image_attrs)

Full example: image resource create

Create Image via interoperable image import process¶

Create an image then use interoperable image import process to download data from a web URL.

For more information about the image import process, please check interoperable image import

def import_image(conn):
    print("Import Image:")

    # Url where glance can download the image
    uri = 'https://download.cirros-cloud.net/0.4.0/' \
          'cirros-0.4.0-x86_64-disk.img'

    # Build the image attributes and import the image.
    image_attrs = {
        'name': EXAMPLE_IMAGE_NAME,
        'disk_format': 'qcow2',
        'container_format': 'bare',
        'visibility': 'public',
    }
    image = conn.image.create_image(**image_attrs)
    conn.image.import_image(image, method="web-download", uri=uri)

Full example: image resource import

Downloading an Image with stream=True¶

As images are often very large pieces of data, storing their entire contents in the memory of your application can be less than desirable. A more efficient method may be to iterate over a stream of the response data.

By choosing to stream the response content, you determine the chunk_size that is appropriate for your needs, meaning only that many bytes of data are read for each iteration of the loop until all data has been consumed. See requests.Response.iter_content() for more information.

When you choose to stream an image download, openstacksdk is no longer able to compute the checksum of the response data for you. This example shows how you might do that yourself, in a very similar manner to how the library calculates checksums for non-streamed responses.

def download_image_stream(conn):
    print("Download Image via streaming:")

    # Find the image you would like to download.
    image = conn.image.find_image("myimage")

    # As the actual download now takes place outside of the library
    # and in your own code, you are now responsible for checking
    # the integrity of the data. Create an MD5 has to be computed
    # after all of the data has been consumed.
    md5 = hashlib.md5()

    with open("myimage.qcow2", "wb") as local_image:
        response = conn.image.download_image(image, stream=True)

        # Read only 1024 bytes of memory at a time until
        # all of the image data has been consumed.
        for chunk in response.iter_content(chunk_size=1024):

            # With each chunk, add it to the hash to be computed.
            md5.update(chunk)

            local_image.write(chunk)

        # Now that you've consumed all of the data the response gave you,
        # ensure that the checksums of what the server offered and
        # what you downloaded are the same.
        if response.headers["Content-MD5"] != md5.hexdigest():
            raise Exception("Checksum mismatch in downloaded content")

Downloading an Image with stream=False¶

If you wish to download an image’s contents all at once and to memory, simply set stream=False, which is the default.

def download_image(conn):
    print("Download Image:")

    # Find the image you would like to download.
    image = conn.image.find_image("myimage")

    with open("myimage.qcow2", "w") as local_image:
        response = conn.image.download_image(image)

        # Response will contain the entire contents of the Image.
        local_image.write(response)

Full example: image resource download

Delete Image¶

Delete an image.

def delete_image(conn):
    print("Delete Image:")

    example_image = conn.image.find_image(EXAMPLE_IMAGE_NAME)

    conn.image.delete_image(example_image, ignore_missing=False)

Full example: image resource delete

this page last updated: 2019-02-25 15:53:00

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