Add support for Glance v2 API

Add support for Glance v2 API

https://blueprints.launchpad.net/nova/+spec/use-glance-v2-api

This spec proposes to add the ability for Nova to use the Glance v2 API, and starts the deprecation period for the support of the Glance v1 API.

While parts of Nova already use the Glance v2 API, this is about making the dependency on Glance v1 API optional, so it can be removed completely in a future release.

Problem description

Glance relegated v1 from CURRENT to SUPPORTED status in Kilo. Currently Nova requires access to the Glance v1 API. Glance would like to deprecate that API in Newton cycle, so to help that effort Nova should stop using Glance v1 API.

v1 is considered unsuitable for exposing to public for a number of reasons, but to name a few:

  • image schema isn’t exposed,

  • list all images call shows details including all properties on image that may result into slow queries or even worse,

  • operators don’t have a way to specify certain important properties (via schema again) as a part of their deployment,

  • tags API isn’t exposed as recommended by the API_WG and therefore ,

  • no possibility to sort by multiple fields,

  • and a lot more!

To allow for a smooth upgrade, we need to ensure Newton supports using both Glance v1 and Glance v2, to give deployers time to ensure they have Glance v2 deployed in a way that can be used by Nova.

While some areas of Nova already make use of Glance v2, there are many areas of Nova that still have a hard dependency on Glance v1. The key areas that still use Glance v1 include:

  • Nova’s Image API, that is effectively just a proxy of Glance’s v1 API,

  • Virt driver specific download of images and upload of images,

  • CRUD operations on image metadata,

  • Creating and deleting snapshots in common code.

Before we can stop Nova requiring Glance v1 and fully deprecate the requirement for Glance v1, we need to remove all the above uses of Glance v1.

Note

Nova’s external API must keep compatibility regardless of whether it is using Glance v1 or Glance v2, to allow for a smooth upgrade between releases.

Use Cases

Currently, Nova deployers are forced to install both Glance v1 and Glance v2. This is because Nova currently requires Glance v1, but for the reason of its obvious disadvantages only Glance v2 is considered safe to be exposed publicly to End Users.

It is assumed that Nova’s lack of support for Glance v2 is causing confusion that is holding people back from deploying Glance v2. This in turn is causing some problems for the DefCore effort.

Proposed change

Support for Glance v2 will be done within the Nova code.

Note

Because Glance v1 is moving to DEPRECATED and will be removed, the code in Nova should be written to optimize the ease of deleting Glance v1 code in the future. That means making v1 / v2 API decision very early in the code flow, and not combining v1 / v2 handling into common methods.

Constraints

The Nova Images API still needs to work (within reason). It should be moved to be backed by Glance v2. The case sensitivity issue regarding metadata is a known issue once the proxy starts using Glance V2 APIs in the backend.

A Nova installation should always work on only one version of the Glance API in production. Flipping back and forth deep in the code adds a lot of complexity.

Xen virt driver requires a helper in dom0 that runs python 2.4.

Detailed Changes

Introduce a CONF item use_glance_v1=True under the [glance] section. This will remove the need for auto discovery of Glance API version The api_servers config specifies versionless API servers today, so is consistent with that. The conf parameter will be deprecated once we have a CI job that disables glance v1 API and enables glance V2 APIs by setting the flag to False and eventually passes all the tests.

If there are differences in the code between glance v1 / v2 methods and classes should be built independently for the glance v1 vs. v2 interaction. This allows us to delete the v1 code in the future easily.

Alternatives

None.

Data model impact

None.

REST API impact

The Nova Images API will have incompatibility when it comes to case sensitivity of metadata. This is unavoidable.

Security impact

None.

Notifications impact

None.

Other end user impact

End user must remember about several incompatibilities between v1 and v2 apis:

  • Image properties in v1 are passed with http headers which makes them case insensitive. In v2 image info is passed as json document and ‘MyProperty’ and ‘myproperty’ are two different properties.

  • in v1 user can create custom properties like ‘owner’ or ‘created_at’ and they are stored in special dictionary ‘properties’. v2 images have flat structure, which means that all custom properties are located on the same level as base properties. It leads to the fact if v1 image has a custom property that has a name coincided with the name of base property, then this property will be ignored in v2. Example output differences:

    • v1 image output:

      {
        "name": "image_name",
        "owner": "image_owner"
        "properties":
           {
              "name": "just a custom property",
              "owner": "another custom property",
              "licence": "gpl v2",
           }
      }
      
    • v2 image output:

      {
        "name": "image_name",
        "owner": "image_owner"
        "licence": "gpl v2",
      }
      

The Nova proxy should have code to ensure that the V1 output format is preserved even while working with Glance V2 APIs in the backend.

  • v2 forbids for user to specify some image properties like id or size.

Performance Impact

None.

Other deployer impact

None.

Developer impact

None.

Implementation

Assignee(s)

Primary assignee:

mfedosin

Other contributors:

flaper87 sudipto nikhil-komawar

Work Items

  • Introduce a top level boolean flag to segregate the Glance V1 and V2 paths. The boolean use_glance_v1 is set to True by default to ensure that Glance V1 APIs are used by default. Once the boolean is flipped to False, the Nova proxy shall start using the Glance V2 APIs.

  • Introduce GlanceImageServiceV2 as a similar class to GlanceImageService There is expected code duplication across these two above classes however, once the V1 APIs are deprecated, all the code related to GlanceImageService should be deleted.

  • Do the following code re-factor to ensure that the output of CRUD operations on the Glance V2 APIs remains consistent with the existing Nova proxy output that uses Glance V1 by default:

    • Add another ‘schema-based’ handler, that transforms glance v2 image output to format adopted in nova.image.

    • Add additional handlers that transforms v1 image filters in v2. Related feature request: https://bugs.launchpad.net/nova/+bug/1201266

    • Add transformation to 2-stepped image creation (creation of the record in db + file uploading).

    • Add special handler for creating active images with size ‘0’ without image data.

    • Add the ability to set custom location for an image. It’s required for libvirt driver, for Ceph backends.

      Note

      show_multiple_locations option must be enabled in glance config in order for this to work. In v1 setting custom locations is enabled by default for for v2 this option must be activated explicitly. Related policies must be modified to allow this.

    • Add special handler to remove custom properties from the image: purge_props flag in v1 vs. props_to_remove list in v2.

  • Adapt Xen virt driver to support v2 api.

  • Ensure the rest of the code base can use the existing image code to talk to either Glance v1 or Glance v2, defaulting to Glance V1 and subsequently switching to Glance V2 as mentioned above.

  • Ensure all the virt drivers either support Glance v2 or fallback to v1.

  • Add a deprecation warning in the logs if users run with Glance v1.

Dependencies

Bug https://bugs.launchpad.net/nova/+bug/1539698 must be fixed before code is merged.

Testing

The gate jobs today enable glance v1 and v2. The CONF.glance.use_glance_v1 option defaults to True so patches will test against v1. Then we’ll add a job that disables glance v1 and enables only glance v2, and configures nova to set CONF.glance.use_glance_v1=False and we’ll run that job against the top-level change in the glance v2 integration series.

At that point we deprecate the use_glance_v1 option once we know it’s passing tests with the v2 stack only.

Documentation Impact

  • Glance API version configuration option needs to be documented

  • Release Notes should note the partial deprecation of Glance v1 support

  • Release Note should warn about any virt drivers that are unable to run with Glance v2.

  • Docs should be updated to highlight the case sensitivity problems as noted earlier in the spec.

References

None.

History

Revisions

Release Name

Description

Liberty

Introduced

Mitaka

Partial implemented

Newton

Re-proposed

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