Config drive based on image property

Config drive based on image property

https://blueprints.launchpad.net/nova/+spec/config-drive-image-property

When creating an instance, check the image property to decide if a config drive should be created.

Problem description

Currently Nova decides if config drive is created for a server based on:

  1. If the user specifies the config-drive option in server create API request, or,

  2. If the server is scheduled to a compute node with force_config_drive option set.

But we need consider the image requirement also. Some images may explicitly require config drive.

Proposed change

  • Add an image property as “img_config_drive”, the value of the img_config_drive can be:

    • img_config_drive=mandatory|optional

    where these mean:

    • mandatory == instance must always have a config drive

    • optional == instance can use a config drive, but can still work if missing

    Any other value will be treated as error. If no option specified, the default value is optional.

    In future, this property may be extended to include more choices like ‘disable’ to disable config_drive. A mechanism should be presented at that time to make sure the ‘disable’ option is not treated as error.

  • The rule of config drive decision is described as followed table. A config drive will be created whenever user specified in API, required in image property or compute node configuration option specified it.

    API

    Image Property

    Compute Config

    Result

    No

    Mandatory

    Set or Unset

    Yes

    No

    Optional

    Set

    Yes

    No

    Optional

    Unset

    No

    Specified

    Mandatory or Optional

    Set or Unset

    Yes

Alternatives

Another option is to combine the API option and image property into one instance property in the API layer, but this is not clean IMHO.

Data model impact

No

REST API impact

No

Security impact

No

Notifications impact

No

Other end user impact

This BP will add one more image property, so user should be aware of that.

Performance Impact

There will be no performance impact.

Other deployer impact

It’s recommended that deployers update all compute nodes before they add the config drive property to any images. Otherwise, the image property is not checked by compute node w/o this features.

Developer impact

No

Implementation

Assignee(s)

Primary assignee:

yunhong-jiang

Work Items

  • Change the virt/configdrive.py to check image property also.

Dependencies

There are some discussion of the enhancement of image property as in https://blueprints.launchpad.net/nova/+spec/convert-image-meta-into-nova-object and the discussion is on-going.

This proposal is not conflict with that proposal, we just need make sure the new config drive property will be defined in the VirtProperties. It will be a small effort no matter which proposal lands firstly.

Testing

Tempest tests will be added so that we can make sure the image config drive property is treated correctly.

Documentation Impact

Document change needed for the new image property.

References

No

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nova-specs