Using Glance’s Image Public APIs

Glance is the reference implementation of the OpenStack Images API. As such, Glance fully implements versions 1 and 2 of the Images API.

There used to be a sentence here saying, “The Images API specification is developed alongside Glance, but is not considered part of the Glance project.” That’s only partially true (or completely false, depending upon how strict you are about these things). Conceptually, the OpenStack Images API is an independent definition of a REST API. In practice, however, the only way to participate in the evolution of the Images API is to work with the Glance community to define the new functionality and provide its reference implementation. Further, Glance falls under the “designated sections” provision of the OpenStack DefCore Guidelines, which basically means that in order to qualify as “OpenStack”, a cloud exposing an OpenStack Images API must include the Glance Images API implementation code. Thus, although conceptually independent, the OpenStack Images APIs are intimately associated with Glance.

References

Glance and the Images APIs: Past, Present, and Future

Here’s a quick summary of the Images APIs that have been implemented by Glance. If you’re interested in more details, you can consult the Release Notes for all the OpenStack releases (beginning with “Bexar”) to follow the evolution of features in Glance and the Images APIs.

Images v1 API

The v1 API was originally designed as a service API for use by Nova and other OpenStack services. In the Kilo release, the v1.1 API was downgraded from CURRENT to SUPPORTED. The Images v1 API is closed to further development, and the Glance code implementing the v1 API accepts only serious bugfixes.

It’s possible to deploy OpenStack without exposing the Images v1 API to end users. The Compute v2 API contains image-related API calls allowing users to list images, list images details, show image details for a specific image, delete images, and manipulate image metadata. Nova acts as a proxy to Glance for these image-related calls. It’s important to note that the image-related calls in the Compute v2 API are a proper subset of the calls available in the Images APIs.

Currently Nova uses the Images v1 API, but work is in progress to convert Nova (and other OpenStack services that consume images) to using the Images v2 API. Once that occurs, it will be possible to deploy OpenStack without deploying the Images v1 API. At that point, the Images v1 API will be deprecated, following the standard OpenStack deprecation policy.

Reference

Images v2 API

The v2 API is the CURRENT OpenStack Images API. It provides a more friendly interface to consumers than did the v1 API, as it was specifically designed to expose images-related functionality as a public-facing endpoint. It’s the version that’s currently open to development.

A common strategy is to deploy multiple Glance nodes: internal-facing nodes providing both Images v1 and v2 APIs for internal consumers like Nova, and external-facing nodes providing only the Images v2 API for public use. Thus, there is no reason to rely solely on Nova’s image-related calls in the Compute API if one does not want to expose the Images v1 API to public endpoints.

The Future

During the long and tumultuous design phase of what has since become an independent service named “Glare” (the Glance Artifacts Repository), the Glance community loosely spoke about the Artifacts API being “Glance v3”. This, however, was only a shorthand way of speaking of the Artifacts effort. The Artifacts API can’t be the Images v3 API since Artifacts are not the same as Images. Conceptually, a virtual machine image could be an Artifact, and the Glare code has been designed to be compatible with the Images v2 API. But at this time, there are no plans to implement an Images v3 API.

As far as the Glance/Glare relationship goes, it’s too early to say what the future holds. While it’s evident that there’s a need for an Artifact Repository in OpenStack, whether it will be as ubiquitous as the need for an Images Repository isn’t clear. On the other hand, industry trends could go in the opposite direction where everyone needs Artifacts and deployers view images as simply another type of digital artifact. As Yogi Berra, an experienced manager, once said, “It’s tough to make predictions, especially about the future.”

Authentication

Glance depends on Keystone and the OpenStack Identity API to handle authentication of clients. You must obtain an authentication token from Keystone using and send it along with all API requests to Glance through the X-Auth-Token header. Glance will communicate back to Keystone to verify the token validity and obtain your identity credentials.

See Authentication With Keystone for more information on integrating with Keystone.

Using v1.X

For the purpose of examples, assume there is a Glance API server running at the URL http://glance.example.com on the default port 80.

List Available Images

We want to see a list of available images that the authenticated user has access to. This includes images owned by the user, images shared with the user and public images.

We issue a GET request to http://glance.example.com/v1/images to retrieve this list of available images. The data is returned as a JSON-encoded mapping in the following format:

{'images': [
  {'uri': 'http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9',
   'name': 'Ubuntu 10.04 Plain',
   'disk_format': 'vhd',
   'container_format': 'ovf',
   'size': '5368709120'}
  ...]}

List Available Images in More Detail

We want to see a more detailed list of available images that the authenticated user has access to. This includes images owned by the user, images shared with the user and public images.

We issue a GET request to http://glance.example.com/v1/images/detail to retrieve this list of available images. The data is returned as a JSON-encoded mapping in the following format:

{'images': [
  {'uri': 'http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9',
   'name': 'Ubuntu 10.04 Plain 5GB',
   'disk_format': 'vhd',
   'container_format': 'ovf',
   'size': '5368709120',
   'checksum': 'c2e5db72bd7fd153f53ede5da5a06de3',
   'created_at': '2010-02-03 09:34:01',
   'updated_at': '2010-02-03 09:34:01',
   'deleted_at': '',
   'status': 'active',
   'is_public': true,
   'min_ram': 256,
   'min_disk': 5,
   'owner': null,
   'properties': {'distro': 'Ubuntu 10.04 LTS'}},
  ...]}

Note

All timestamps returned are in UTC.

The updated_at timestamp is the timestamp when an image’s metadata was last updated, not its image data, as all image data is immutable once stored in Glance.

The properties field is a mapping of free-form key/value pairs that have been saved with the image metadata.

The checksum field is an MD5 checksum of the image file data.

The is_public field is a boolean indicating whether the image is publicly available.

The min_ram field is an integer specifying the minimum amount of RAM needed to run this image on an instance, in megabytes.

The min_disk field is an integer specifying the minimum amount of disk space needed to run this image on an instance, in gigabytes.

The owner field is a string which may either be null or which will indicate the owner of the image.

Filtering Images Lists

Both the GET /v1/images and GET /v1/images/detail requests take query parameters that serve to filter the returned list of images. The following list details these query parameters.

  • 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

  • disk_format=FORMAT

    Filters images having a disk_format attribute matching FORMAT

    For more information, see About Disk and Container Formats

  • status=STATUS

    Filters images having a status attribute matching STATUS

    For more information, see About Image 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

These two resources also accept additional query parameters:

  • sort_key=KEY

    Results will be ordered by the specified image attribute KEY. Accepted values include id, name, status, disk_format, container_format, size, created_at (default) and updated_at.

  • sort_dir=DIR

    Results will be sorted in the direction DIR. Accepted values are asc for ascending or desc (default) for descending.

  • marker=ID

    An image identifier marker may be specified. When present, only images which occur after the identifier ID will be listed. (These are the images that have a sort_key later than that of the marker ID in the sort_dir direction.)

  • limit=LIMIT

    When present, the maximum number of results returned will not exceed LIMIT.

Note

If the specified LIMIT exceeds the operator defined limit (api_limit_max) then the number of results returned may be less than LIMIT.

  • is_public=PUBLIC

    An admin user may use the is_public parameter to control which results are returned.

    When the is_public parameter is absent or set to True the following images will be listed: Images whose is_public field is True, owned images and shared images.

    When the is_public parameter is set to False the following images will be listed: Images (owned, shared, or non-owned) whose is_public field is False.

    When the is_public parameter is set to None all images will be listed irrespective of owner, shared status or the is_public field.

Note

Use of the is_public parameter is restricted to admin users. For all other users it will be ignored.

Retrieve Image Metadata

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 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 image returned, we can issue a HEAD request to the Glance server for the image’s URI.

We issue a HEAD request to http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9 to retrieve complete metadata for that image. The metadata is returned as a set of HTTP headers that begin with the prefix x-image-meta-. The following shows an example of the HTTP headers returned from the above HEAD request:

x-image-meta-uri              http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9
x-image-meta-name             Ubuntu 10.04 Plain 5GB
x-image-meta-disk_format      vhd
x-image-meta-container_format ovf
x-image-meta-size             5368709120
x-image-meta-checksum         c2e5db72bd7fd153f53ede5da5a06de3
x-image-meta-created_at       2010-02-03 09:34:01
x-image-meta-updated_at       2010-02-03 09:34:01
x-image-meta-deleted_at
x-image-meta-status           available
x-image-meta-is_public        true
x-image-meta-min_ram          256
x-image-meta-min_disk         0
x-image-meta-owner            null
x-image-meta-property-distro  Ubuntu 10.04 LTS

Note

All timestamps returned are in UTC.

The x-image-meta-updated_at timestamp is the timestamp when an image’s metadata was last updated, not its image data, as all image data is immutable once stored in Glance.

There may be multiple headers that begin with the prefix x-image-meta-property-. These headers are free-form key/value pairs that have been saved with the image metadata. The key is the string after x-image-meta-property- and the value is the value of the header.

The response’s ETag header will always be equal to the x-image-meta-checksum value.

The response’s x-image-meta-is_public value is a boolean indicating whether the image is publicly available.

The response’s x-image-meta-owner value is a string which may either be null or which will indicate the owner of the image.

Retrieve Raw Image Data

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

We have queried the Glance server for a list of 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 image returned, we can issue a HEAD request to the Glance server for the image’s URI.

We issue a GET request to http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9 to retrieve metadata for that image as well as the image itself encoded into the response body.

The metadata is returned as a set of HTTP headers that begin with the prefix x-image-meta-. The following shows an example of the HTTP headers returned from the above GET request:

x-image-meta-uri              http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9
x-image-meta-name             Ubuntu 10.04 Plain 5GB
x-image-meta-disk_format      vhd
x-image-meta-container_format ovf
x-image-meta-size             5368709120
x-image-meta-checksum         c2e5db72bd7fd153f53ede5da5a06de3
x-image-meta-created_at       2010-02-03 09:34:01
x-image-meta-updated_at       2010-02-03 09:34:01
x-image-meta-deleted_at
x-image-meta-status           available
x-image-meta-is_public        true
x-image-meta-min_ram          256
x-image-meta-min_disk         5
x-image-meta-owner            null
x-image-meta-property-distro  Ubuntu 10.04 LTS

Note

All timestamps returned are in UTC.

The x-image-meta-updated_at timestamp is the timestamp when an image’s metadata was last updated, not its image data, as all image data is immutable once stored in Glance.

There may be multiple headers that begin with the prefix x-image-meta-property-. These headers are free-form key/value pairs that have been saved with the image metadata. The key is the string after x-image-meta-property- and the value is the value of the header.

The response’s Content-Length header shall be equal to the value of the x-image-meta-size header.

The response’s ETag header will always be equal to the x-image-meta-checksum value.

The response’s x-image-meta-is_public value is a boolean indicating whether the image is publicly available.

The response’s x-image-meta-owner value is a string which may either be null or which will indicate the owner of the image.

The image data itself will be the body of the HTTP response returned from the request, which will have content-type of application/octet-stream.

Add a New 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 API. Assuming, like in the examples above, that a Glance API server is running at glance.example.com, we issue a POST request to add an image to Glance:

POST http://glance.example.com/v1/images

The metadata about the image is sent to Glance in HTTP headers. The body of the HTTP request to the Glance API will be the MIME-encoded disk image data.

Reserve a New Image

We can also perform the activities described in Add a New Image using two separate calls to the Image API; the first to register the image metadata, and the second to add the image disk data. This is known as “reserving” an image.

The first call should be a POST to http://glance.example.com/v1/images, which will result in a new image id being registered with a status of queued:

{'image':
 {'status': 'queued',
  'id': '71c675ab-d94f-49cd-a114-e12490b328d9',
  ...}
 ...}

The image data can then be added using a PUT to http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9. The image status will then be set to active by Glance.

Image Metadata in HTTP Headers

Glance will view as image metadata any HTTP header that it receives in a POST request where the header key is prefixed with the strings x-image-meta- and x-image-meta-property-.

The list of metadata headers that Glance accepts are listed below.

  • x-image-meta-name

    This header is required, unless reserving an image. 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.

  • x-image-meta-id

    This header is optional.

    When present, Glance will use the supplied identifier for the image. If the identifier already exists in that Glance node, then a 409 Conflict will be returned by Glance. The value of the header must be a uuid in hexadecimal string notation (that is 71c675ab-d94f-49cd-a114-e12490b328d9).

    When this header is not present, Glance will generate an identifier for the image and return this identifier in the response (see below).

  • x-image-meta-store

    This header is optional. Valid values are one of file, s3, rbd, swift, cinder, sheepdog or vsphere.

    When present, Glance will attempt to store the disk image data in the backing store indicated by the value of the header. If the Glance node does not support the backing store, Glance will return a 400 Bad Request.

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

  • x-image-meta-disk_format

    This header is required, unless reserving an image. Valid values are one of aki, ari, ami, raw, iso, vhd, vdi, qcow2, or vmdk.

    For more information, see About Disk and Container Formats.

  • x-image-meta-container_format

    This header is required, unless reserving an image. Valid values are one of aki, ari, ami, bare, ova, ovf, or docker.

    For more information, see About Disk and Container Formats.

  • x-image-meta-size

    This header is optional.

    When present, Glance assumes that the expected size of the request body will be the value of this header. If the length in bytes of the request body does not match the value of this header, Glance will return a 400 Bad Request.

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

  • x-image-meta-checksum

    This header is optional. When present, it specifies the MD5 checksum of the image file data.

    When present, Glance will verify the checksum generated from the back-end store while storing your image against this value and return a 400 Bad Request if the values do not match.

  • x-image-meta-is_public

    This header is optional.

    When Glance finds the string “true” (case-insensitive), the image is marked as a public one, 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 owned by a user.

  • x-image-meta-min_ram

    This header is optional. When present, it specifies the minimum amount of RAM in megabytes required to run this image on a server.

    When not present, the image is assumed to have a minimum RAM requirement of 0.

  • x-image-meta-min_disk

    This header is optional. When present, it specifies the expected minimum disk space in gigabytes required to run this image on a server.

    When not present, the image is assumed to have a minimum disk space requirement of 0.

  • x-image-meta-owner

    This header is optional and only meaningful for admins.

    Glance normally sets the owner of an image to be the tenant or user (depending on the “owner_is_tenant” configuration option) of the authenticated user issuing the request. However, if the authenticated user has the Admin role, this default may be overridden by setting this header to null or to a string identifying the owner of the image.

  • x-image-meta-property-*

    When Glance receives any HTTP header whose key begins with the string prefix x-image-meta-property-, Glance adds the key and value to a set of custom, free-form image properties stored with the image. The key is a lower-cased string following the prefix x-image-meta-property- with dashes and punctuation replaced with underscores.

    For example, if the following HTTP header were sent:

    x-image-meta-property-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. However, keep in mind that the 8K limit on the size of all the HTTP headers sent in a request will effectively limit the number of image properties.

Update an Image

Glance will consider any HTTP header that it receives in a PUT request as an instance of image metadata. In this case, the header key should be prefixed with the strings x-image-meta- and x-image-meta-property-.

If an image was previously reserved, and thus is in the queued state, then image data can be added by including it as the request body. If the image already has data associated with it (for example, it is not in the queued state), then including a request body will result in a 409 Conflict exception.

On success, the PUT request will return the image metadata encoded as HTTP headers.

See more about image statuses here: Image Statuses

List Image Memberships

We want to see a list of the other system tenants (or users, if “owner_is_tenant” is False) that may access a given virtual machine image that the Glance server knows about. We take the uri field of the image data, append /members to it, and issue a GET request on the resulting URL.

Continuing from the example above, in order to get the memberships for the first image returned, we can issue a GET request to the Glance server for http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9/members. And we will get back JSON data such as the following:

{'members': [
 {'member_id': 'tenant1',
  'can_share': false}
 ...]}

The member_id field identifies a tenant with which the image is shared. If that tenant is authorized to further share the image, the can_share field is true.

List Shared Images

We want to see a list of images which are shared with a given tenant. We issue a GET request to http://glance.example.com/v1/shared-images/tenant1. We will get back JSON data such as the following:

{'shared_images': [
 {'image_id': '71c675ab-d94f-49cd-a114-e12490b328d9',
  'can_share': false}
 ...]}

The image_id field identifies an image shared with the tenant named by member_id. If the tenant is authorized to further share the image, the can_share field is true.

Add a Member to an Image

We want to authorize a tenant to access a private image. We issue a PUT request to http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9/members/tenant1. With no body, this will add the membership to the image, leaving existing memberships unmodified and defaulting new memberships to have can_share set to false. We may also optionally attach a body of the following form:

{'member':
 {'can_share': true}
}

If such a body is provided, both existing and new memberships will have can_share set to the provided value (either true or false). This query will return a 204 (“No Content”) status code.

Remove a Member from an Image

We want to revoke a tenant’s right to access a private image. We issue a DELETE request to http://glance.example.com/v1/images/1/members/tenant1. This query will return a 204 (“No Content”) status code.

Replace a Membership List for an Image

The full membership list for a given image may be replaced. We issue a PUT request to http://glance.example.com/v1/images/71c675ab-d94f-49cd-a114-e12490b328d9/members with a body of the following form:

{'memberships': [
 {'member_id': 'tenant1',
  'can_share': false}
 ...]}

All existing memberships which are not named in the replacement body are removed, and those which are named have their can_share settings changed as specified. (The can_share setting may be omitted, which will cause that setting to remain unchanged in the existing memberships.) All new memberships will be created, with can_share defaulting to false unless it is specified otherwise.

Image Membership Changes in Version 2.0

Version 2.0 of the Images API eliminates the can_share attribute of image membership. In the version 2.0 model, image sharing is not transitive.

In version 2.0, image members have a status attribute that reflects how the image should be treated with respect to that image member’s image-list.

  • The status attribute may have one of three values: pending, accepted, or rejected.
  • By default, only those shared images with status accepted are included in an image member’s image-list.
  • Only an image member may change his/her own membership status.
  • Only an image owner may create members on an image. The status of a newly created image member is pending. The image owner cannot change the status of a member.

Distinctions from Version 1.x API Calls

  • The response to a request to list the members of an image has changed.

    call: GET on /v2/images/{imageId}/members

    response: see the JSON schema at /v2/schemas/members

  • The request body in the call to create an image member has changed.

    call: POST to /v2/images/{imageId}/members

    request body:

    { "member": "<MEMBER_ID>" }
    

    where the {memberId} is the tenant ID of the image member.

    The member status of a newly created image member is pending.

New API Calls

  • Change the status of an image member

    call: PUT on /v2/images/{imageId}/members/{memberId}

    request body:

    { "status": "<STATUS_VALUE>" }
    

    where <STATUS_VALUE> is pending, accepted, or rejected. The {memberId} is the tenant ID of the image member.

Images v2 Tasks API

Version 2 of the OpenStack Images API introduces a Task resource that is used to create and monitor long-running asynchronous image-related processes. See the Tasks section of the Glance documentation for more information.

The following Task calls are available:

Create a Task

A user wants to initiate a task. The user issues a POST request to /v2/tasks. The request body is of Content-type application/json and must contain the following fields:

  • type: a string specified by the enumeration defined in the Task schema
  • input: a JSON object. The content is defined by the cloud provider who has exposed the endpoint being contacted

The response is a Task entity as defined by the Task schema. It includes an id field that can be used in a subsequent call to poll the task for status changes.

A task is created in pending status.

Show a Task

A user wants to see detailed information about a task the user owns. The user issues a GET request to /v2/tasks/{taskId}.

The response is in application/json format. The exact structure is given by the task schema located at /v2/schemas/task.

List Tasks

A user wants to see what tasks have been created in his or her project. The user issues a GET request to /v2/tasks.

The response is in application/json format. The exact structure is given by the task schema located at /v2/schemas/tasks.

Note that, as indicated by the schema, the list of tasks is provided in a sparse format. To see more information about a particular task in the list, the user would use the show task call described above.

Filtering and Sorting the Tasks List

The GET /v2/tasks request takes query parameters that server to filter the returned list of tasks. The following list details these query parameters.

  • status={status}

    Filters the list to display only those tasks in the specified status. See the task schema or the Task Statuses section of this documentation for the legal values to use for {status}.

    For example, a request to GET /v2/tasks?status=pending would return only those tasks whose current status is pending.

  • type={type}

    Filters the list to display only those tasks of the specified type. See the enumeration defined in the task schema for the legal values to use for {type}.

    For example, a request to GET /v2/tasks?type=import would return only import tasks.

  • sort_dir={direction}

    Sorts the list of tasks according to updated_at datetime. Legal values are asc (ascending) and desc (descending). By default, the task list is sorted by created_at time in descending chronological order.

API Message Localization

Glance supports HTTP message localization. For example, an HTTP client can receive API messages in Chinese even if the locale language of the server is English.

How to use it

To receive localized API messages, the HTTP client needs to specify the Accept-Language header to indicate the language that will translate the message. For more information about Accept-Language, please refer to http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html

A typical curl API request will be like below:

curl -i -X GET -H 'Accept-Language: zh' -H 'Content-Type: application/json'
http://127.0.0.1:9292/v2/images/aaa

Then the response will be like the following:

HTTP/1.1 404 Not Found
Content-Length: 234
Content-Type: text/html; charset=UTF-8
X-Openstack-Request-Id: req-54d403a0-064e-4544-8faf-4aeef086f45a
Date: Sat, 22 Feb 2014 06:26:26 GMT

<html>
<head>
<title>404 Not Found</title>
</head>
<body>
<h1>404 Not Found</h1>
&#25214;&#19981;&#21040;&#20219;&#20309;&#20855;&#26377;&#26631;&#35782; aaa &#30340;&#26144;&#20687;<br /><br />
</body>
</html>

Note

Make sure to have a language package under /usr/share/locale-langpack/ on the target Glance server.