Cloned from launchpad blueprint https://blueprints.launchpad.net/glance/+spec/task-of-image-action.

Description:

By current implement, Glance will "kill" the image if there is a upload failure. And end user can't see the image anymore if the image state is marked "killed". So instead of "killing" an image when something goes wrong during data upload, we need a better way to let end user query the image failed to upload and notify the user. More info, please refer this link: https://blueprints.launchpad.net/glance/+spec/image-error-state-management

Based on the discussion with markwash, we prefer to add "task" instead of a new "error" state to track the life cycle of image actions. And one of the reasons is "error" state means the image is in an "unrecoverable" state.  But in real, the image create action should be able continue by retry/re-upload.

So a typical work flow maybe like below:
1. User submit a command that processes asynchronously to Glance, in the return response there should be /v2/tasks/<id>.
2. User can do GET /v2/tasks/<id> to track the status of this action, including find out any errors
3. The task will be persist. 
     3.1 If the action is executed successfully.
     3.2 If the action failed, the error log will be saved, including the error details. 

For now, Nova is using "action" and "fault" to resolve this kind of issue, so it can be referenced for this design.

Specification URL (additional information):

None