openstack/nova
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e906a8c0ec
nova/doc/source/reference/attach-volume.rst
Lee Yarwood b62f9a04a0 Add os-volume_attachments reference docs 
This change adds a simple sequence diagram showing the flow of a volume
attachment between the various services, using the libvirt driver as an
example virt driver.

Change-Id: I631ac9de3d48aa0ad849f6615d0ad2052cb63e80
2020-11-09 17:12:48 +00:00

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Attaching Volumes

The following sequence diagram outlines the current flow when attaching a volume to an instance using the os-volume_attachments API. This diagram uses the libvirt driver as an example virt driver to additionally document the optional interactions with the os-brick library on the compute hosts during the request.

Note

os-brick is not always used to connect volumes to the host, most notibly when connecting an instance natively to ceph rbd volumes

The diagram also outlines the various locks taken on the compute during the attach volume flow. In this example these include locks against the instance.uuid, cinder_backend.uuid orchestrated for nova-compute by os-brick and the generic connect_volume lock taken within os-brick itself. This final connect_volume lock also being held when detaching and disconnecting a volume from the host by os-brick.

attach_volume.diag