Comment 2 for bug 1857306

I'm also wondering what the behavior was with this prior to cells v2. I suppose the API would create the instance in the nova DB and check osapi_compute_unique_server_name_scope which would result in an error response to the user. With cells v2 the instance creation was moved to conductor after scheduling and that code isn't handling the InstanceExists error from the DB API, nor is the API/build request code checking for osapi_compute_unique_server_name_scope like the DB API.