Operator maintained images lifecycle

Operator maintained images lifecycle

https://blueprints.launchpad.net/glance/+spec/hidden-images

This spec addresses the problem that cloud operators have into keep a public image list with only the latest images versions available.

Problem description

Cloud operators supply public images that can be used by end users to boot servers. An example is an image containing the CentOS 7 operating system. Such images must be updated as security concerns, etc., are addressed. In Glance, however, image data is immutable, so each update results in a new public image. Further, operators do not want to delete the “old” public images, as end users may require them for different use cases like server rebuilds. As a result, the default image-list for end users becomes very large. Further, the default image-list may contain multiple CentOS 7 images, for example, making it difficult for end users to determine which image to use.

Note

Example

An operator provides an image for CentOS 7 with a standard set of packages as image 1. Some minor security problem is discovered in OpenSSL, so the operator provides image 2 of CentOS 7 with updated OpenSSL. Then a kernel vulnerability is discovered and the operator issues image 3 of CentOS 7 with updated OpenSSL and a patched kernel. Each of these is a “version” of the image, but the same version of CentOS 7. The operator wants a new end user to start with image 3, but a user who’s been around a while longer may want to continue to use image 1 and patch/upgrade himself (for example, the OpenSSL update brings in a dependency that conflicts with some key software the user is running). If all three images have public visibility, then all three of them will appear in an end user’s default image-list.

A current practice is to address this by adding a custom property on an image, for example, "is_current": "yes", but this is operator-specific and not interoperable. This only solves part of the problem, however, because end users must be educated to look for the "is_current" image property. It would be better if only those images with "is_current": "yes" were included in the end user’s default image-list in the first place.

Proposed change

This spec proposes adding a new boolean column "os_hidden" in images table. Images where "os_hidden" = True will be omitted from the image list presented to the user. This will apply to all image visibilities. However, the images will continue to be discoverable.

Note

Example

An user wants a CentOS 7 provider image, so he uses: "?visibility=public" on the GET v2/images call. He sees a CentOS 7 image, but notices that it was created_at today, so he realizes that it’s not the same image that he’s searching for. So now he uses "?visibility=public&os_hidden=true" to get the list of all available images.

If the image has "os_hidden" = False the image is not omitted from the image list. It preserves the current behaviour.

At image creation, if not specified, it’s used "os_hidden" = False.

Changing the property “os_hidden” will be considered an image update. Because, the policy is already defined for this operation no other changes are required.

In the response of create/show image the new property will be displayed as os_hidden. If a pre-Rocky image already has a custom property named as os_hidden then that property will no longer be visible in the response from Rocky release.

All operations in the image will continue to be available considering the policy defined.

Alternatives

Instead using a new image property we can have a new visibility = “hidden”. Images with this new visibility state will not be in the default image list. To list images with visibility “hidden” it will be required to explicitly request it. Ex: "property --visibility=hide" Images with the visibility “hidden” will always be discoverable by the user.

This solution is less flexible because visibility “hidden” has potentially the same scope as “public”. The user roles that can use this visibility need to be controlled by policy.

Another approach is to use the proposed new image property “hidden” but not make these images discoverable with the API. However, there is the use case where a project may require a particular image version (for example: different OS releases like CentOS7.4 to CentOS7.5; appliance vendors that support their software on particular images). If “hidden” images are not discoverable cloud admins will need implement their own solution to expose these images.

Data model impact

Add the “os_hidden” boolean column in images table.

For the E-M-C migration strategy is proposed:

  • Triggers: not required. A pre-Rocky glance release will reject an image-update call setting ‘os_hidden’ with a 400 because it doesn’t recognize the field.
  • Expand: will add a boolean “os_hidden” column to the images table.
  • Contract: not required
  • Data Migration: Not required.

REST API impact

A new property “os_hidden” will be accepted for the GET call. GET v2/images … os_hidden=true/false By default the API will consider os_hidden=false.

Security impact

None

Notification impact

None

Other end user impact

The end user needs to be aware that the Cloud provider may “hide” old images. This is specific to each Cloud provider.

Performance impact

None

Developer impact

None

Implementation

Assignee(s)

Primary assignee: - Abhishek Kekane

Work Items

  • Add support in GET call for the property “os_hidden”. Consider the default “os_hidden=false”.
  • Change the image table schema adding a new field.
  • Change the glance-client to support the new property.

Dependencies

None

Testing

TBD

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