It is said that "This API is not supported for volume-backed instances." in "Create Server Back Up" API in the compute API reference.
https://developer.openstack.org/api-ref/compute/#create-server-back-up-createbackup-action
So it is by design. If you want to back up cinder volumes, you can utilize "Create a backup" API in cinder.
https://developer.openstack.org/api-ref/block-storage/v3/index.html#create-a-backup
It is said that "This API is not supported for volume-backed instances." in "Create Server Back Up" API in the compute API reference.
https:/ /developer. openstack. org/api- ref/compute/ #create- server- back-up- createbackup- action
So it is by design.
If you want to back up cinder volumes, you can utilize "Create a backup" API in cinder.
https:/ /developer. openstack. org/api- ref/block- storage/ v3/index. html#create- a-backup