Detaching disk from stopped instance - google-api

Question

I am trying to detach a disk from a stopped instance which is currently holding the disk. here's how I am doing it currently.
def detach_disk_from_instance(disk_name, zone=GCLOUD_ZONE):
disk_info = get_disk_info(disk_name=disk_name, zone=zone)
if disk_info.get('users'):
instance_name = disk_info['users'][0].rsplit('/').pop()
logger.info("detatching disk : {} from instance : {}".format(disk_name, instance_name))
request = compute.instances().detachDisk(
project=GCLOUD_PROJECT_NAME, zone=zone, instance=instance_name, deviceName=disk_name)
return make_http_request(request, {})
def wait_for_operation(operation, zone=GCLOUD_ZONE, worker=1):
logger.info('Waiting for operation {} to finish...'.format(operation))
with ThreadPoolExecutor(worker) as executor:
future = executor.submit(_check_operation_status, operation=operation, zone=zone)
wait([future])
return future.result()
req = detach_disk_from_instance(disk_name='test-disk')
wait_for_operation(operation=req['name'])
above code works if instance which is holding the disk is currently running.
but it doesn't work if instance is stopped. I get the following error when I try to detach disk from a stopped instance.
{'errors': [{'message': "No attached disk found with device name
'test-disk'", 'code': 'INVALID_USAGE'}]}
and I assure you that disk is still attached to the instance and gcp dashboard also shows that.

Answer 1

TL;DR - You're passing the name of the disk resource instead of the device name by which the disk is attached to the instance.
In the instances.attachDisk request to attach a disk to a VM instance you can specify the device name in the deviceName field of the request.
deviceName
string
Specifies a unique device name of your choice that
is reflected into the /dev/disk/by-id/google-* tree of a Linux
operating system running within the instance. This name can be used to
reference the device for mounting, resizing, and so on, from within
the instance.
If not specified, the server chooses a default device name to apply to
this disk, in the form persistent-disks-x, where x is a number
assigned by Google Compute Engine. This field is only applicable for
persistent disks.
You will need to use this name as the deviceName query parameter for the instances.detachDisk request.
Required query parameters
deviceName
string
Disk device name to detach.
As mentioned in the doc, if you did not specify a device name while attaching the disk GCE generates a device name in the form persistent-disks-x and you will have to specify this name.