Allow image to be specified during rescue

https://blueprints.launchpad.net/nova/+spec/allow-image-to-be-specified-during-rescue

In this blueprint we aim to add an additional optional parameter to the instance rescue API. This parameter will be used to specify the image to be used while rescuing the instance. If the parameter is not specified, the instance will be rescued using the base image.

Problem description

The custom image used during rescue might be corrupt, leading to errors, or too large, leading to timeouts. Also, if the base image is deleted, the image ref on the instance_system_metadata will be invalid, leading to the rescue operation failing. This feature can also be used in the case where the customer wants to rescue the instance with a specific image, rather the default one. This would provide more flexibility to the feature.

Proposed change

In order to implement this I propose that we allow the user to specify which image is to be used for rescue. (could be a default base image or a custom image)

Alternatives

None

Data model impact

None

REST API impact

API for specifying image to be used to rescue an instance:

Scenarios: Case 1: If image_ref is specified as part of the rescue request, that image will be used. Case 2: If image_ref is not specified as part of the rescue request, image_base_image_ref on the system_metadata of the instance will be used. (Default behavior)

V2 API specification: POST: v2/{tenant_id}/servers/{server_id}/action

V3 API specification: POST: v3/servers/{server_id}/action

Request parameters: * tenant_id: The ID for the tenant or account in a multi-tenancy cloud. * server_id: The UUID for the server of interest to you. * rescue: Specify the rescue action in the request body. * adminPass(Optional): Use this password for the rescued instance. Generate a new password if none is provided. * rescue_image_ref(Optional): Use this image_ref for rescue.

JSON request: {“rescue”: {“adminPass”: “MySecretPass”, “rescue_image_ref”: “848b39fb-6904-46d6-af3c-baa3eefedffc”}}

JSON response: {“adminPass”: “MySecretPass”}

Sample v2 request: POST: /v2/d1b123/servers/7d14f8123/action -d ‘{“rescue”: {“rescue_image_ref”: “848b39fb-6904-46d6-af3c-baa3eefedffc”}}’

Sample v3 request: POST: /v3/servers/7d14f8123/action -d ‘{“rescue”: {“rescue_image_ref”: “848b39fb-6904-46d6-af3c-baa3eefedffc”}}’

This would use image with ref “848b39fb-6904-46d6-af3c-baa3eefedffc” to rescue instance with uuid “7d14f8123”

JSON schema definition:

rescue = {
    'type': 'object',
    'properties': {
        'rescue': {
            'type': ['object', 'null'],
            'properties': {
                'admin_password': parameter_types.admin_password,
                'rescue_image_ref': parameter_types.image_ref,
            },
            'additionalProperties': False,
        },
    },
    'required': ['rescue'],
    'additionalProperties': False,
}

HTTP response codes: v2: Normal HTTP Response Code: 200 on success v3: Normal HTTP Response Code: 202 on success (Will check whether these can be made consistent in v2 and v3 during implementation.)

Validation: ‘rescue_image_ref’ must be of a uuid-str format. Failure Response Code: HTTPBadRequest with “Invalid image ref format” message.

Security impact

None

Notifications impact

None

Other end user impact

The rescue call in python-novaclient will have to include the additional optional parameter

Optional argument: –rescue_image_ref <image_ref> ID of image to be used for rescue

Performance Impact

None

Other deployer impact

None

Developer impact

The parameter will be optional, so no other code needs to be changed.

Implementation

Assignee(s)

Primary assignee:

aditirav

Work Items

• Changes to be made to the compute manager rescue method to use the image ref passed in, during the rescue of the instance.

• Add an extension to the V2 API to make rescue take in the optional parameter ‘rescue_image_ref

• Changes to the V3 API to take in the optional parameter ‘rescue_image_ref’

• Include tests in tempest to check the behavior of rescue instance with the image ref passed in through the API call.

Dependencies

None

Testing

Tempest tests to be added to check if rescue of the instance uses the image specified in the API call.

Documentation Impact

Changes to be made to the rescue API documentation to include the additional parameter ‘rescue_image_ref’ that can be passed in.

References

None