Implement volume backup/restore for VMDK driver

This specification proposes adding support for backup-create/backup-restore
operations in VMDK driver.

Change-Id: I7ba462a28e8ed4c7a5bbbb4767985e3af17ab2c3
Implements: blueprint vmdk-backup

specs/juno/vmdk-backup.rst

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+..
+ This work is licensed under a Creative Commons Attribution 3.0 Unported
+ License.
+
+ http://creativecommons.org/licenses/by/3.0/legalcode
+
+============================================================
+Support backup and restore of volumes created by VMDK driver
+============================================================
+
+https://blueprints.launchpad.net/cinder/+spec/vmdk-backup
+
+The volumes created by the VMDK driver are virtual disks stored in datastores
+managed by ESX or vCenter server. Currently, the ``backup-create`` and
+``backup-restore`` operations are not supported for these volumes. This
+blueprint proposes adding support for these operations in VMDK driver.
+
+Problem description
+===================
+
+The default implementation of ``backup-create``\\ ``backup-restore`` does the
+following steps:
+
+* Attach the volume as a block device or file.
+
+* Backup\\restore the file by calling backup service.
+
+* Detach the volume.
+
+It uses  an instance of ``InitiatorConnector`` (determined by the back-end
+driver protocol) to do the actual\\detach. There is no  ``InitiatorConnector``
+for the ``vmdk`` protocol and hence the attach\\detach fails for volumes
+created by the VMDK driver. This blueprint proposes adding support for
+``backup-create``\\ ``backup-restore`` for these volumes.
+
+Proposed change
+===============
+
+The change involves overriding the default implementations of ``backup_volume``
+and ``restore_backup`` methods in ``VMwareEsxVmdkDriver``. The steps in
+``backup_volume`` are listed below:
+
+* Create the backing VM if it not found.
+
+* Download the stream-optimized version of the virtual disk corresponding to
+  the volume to a temporary directory.
+
+* Call ``backup_service.backup()`` method to backup the stream-optimized
+  virtual disk file.
+
+* Delete the temporary file.
+
+Following are the steps in ``restore_backup``:
+
+* Call ``backup_service.restore()`` to download the stream-optimized virtual
+  disk file to a temporary directory.
+
+* If the backing VM doesn't exist (in the case of restoring the backup to
+  create a new volume), import the stream-optimized virtual disk file to create
+  a new backing VM.
+
+* If the backing VM exists, import the stream-optimized virtual disk file to
+  create a temporary VM and reconfigure the backing VM to replace its virtual
+  disk with that of the temporary VM.
+
+* Delete the temporary file and temporary VM.
+
+Alternatives
+------------
+
+**HTTP read/write**: It is possible to create an HTTP connection to read/write
+from/to a virtual disk file in vCenter/ESX and an adapter can be written for
+this connection to support some of the file operations required by the backup
+drivers. This implementation works for both Swift and Ceph backup drivers. But
+the TSM backup driver raises ``InvalidBackup`` exception if the volume to be
+backed up is not a block device or regular file.
+
+Data model impact
+-----------------
+
+None
+
+REST API impact
+---------------
+
+None
+
+Security impact
+---------------
+
+None
+
+Notifications impact
+--------------------
+
+None
+
+Other end user impact
+---------------------
+
+None
+
+Performance Impact
+------------------
+
+None
+
+Other deployer impact
+---------------------
+
+None
+
+Developer impact
+----------------
+
+None
+
+
+Implementation
+==============
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  vbala <vbala@vmware.com>
+
+Other contributors:
+  None
+
+Work Items
+----------
+
+* ``backup_volume`` method
+* ``restore_backup`` method
+
+Dependencies
+============
+
+None
+
+
+Testing
+=======
+
+None
+
+Documentation Impact
+====================
+
+None
+
+References
+==========
+
+None