VMware: add support for live migration

This is a proposal for adding support for live migration in the VMware
driver. When the VMware driver is used, each nova-compute is managing a
single vCenter cluster. For the purposes of this proposal we assume that
all nova-computes are managing clusters under the same vCenter server.
Migrating instances across vCenters is supported starting from vSphere
6.0. We can add support for this as a next-step after this blueprint is
implemented.

blueprint vmware-live-migration

Change-Id: I726b22fb92aedb50a25a3ca38ba92048f05f2a17

specs/rocky/approved/vmware-live-migration.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
+
+=====================
+VMware live migration
+=====================
+
+https://blueprints.launchpad.net/nova/+spec/vmware-live-migration
+
+This is a proposal for adding support for live migration in the VMware
+driver. When the VMware driver is used, each nova-compute is managing a
+single vCenter cluster. For the purposes of this proposal we assume that
+all nova-computes are managing clusters under the same vCenter server. If
+migration across different vCenter servers is attempted, an error message
+will be generated and no migration will occur.
+
+Problem description
+===================
+
+Live migration is not supported when the VMware driver is used.
+
+Use Cases
+---------
+
+As an Operator I want to live migrate instances from one compute cluster
+(nova-compute host) to another compute cluster (nova-compute host) in the
+same vCenter server.
+
+Proposed change
+===============
+
+Relocating VMs to another cluster/datastore is a simple matter of calling the
+RelocateVM_Task() vSphere API. The source compute host needs to know the
+cluster name and the datastore regex of the target compute host. If the
+instance is located on a datastore shared between the two clusters, it will
+remain there. Otherwise we will choose a datastore that matches the
+datastore_regex of the target host and migrate the instance there. There will
+be a pre live-migration check that will verify that both source and
+destination compute nodes correspond to clusters in the same vCenter server.
+
+A new object will be introduced (VMwareLiveMigrateData) which will carry the
+host IP, the cluster name and the datastore regex of the target compute host.
+All of them are obtained from the nova config (CONF.vmware.host_ip,
+CONF.vmware.cluster_name and CONF.vmware.datastore_regex).
+
+Alternatives
+------------
+
+None
+
+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
+
+Upgrade impact
+--------------
+
+None
+
+Implementation
+==============
+
+https://review.openstack.org/#/c/270116/
+
+Assignee(s)
+-----------
+
+Primary assignee:
+  rgerganov
+
+Work Items
+----------
+
+* Add ``VMwareLiveMigrateData`` object
+* Implement pre live-migration checks
+* Implement methods for selecting target ESX host and datastore
+* Ensure CI coverage for live-migration
+* Update support-matrix
+
+Dependencies
+============
+
+None
+
+Testing
+=======
+
+The VMware CI will provision two nova-computes and will execute the live
+migration tests from tempest.
+
+Documentation Impact
+====================
+
+The feature support matrix should be updated to indicate that live migration
+is supported with the VMware driver.
+
+References
+==========
+
+http://pubs.vmware.com/vsphere-60/topic/com.vmware.wssdk.apiref.doc/vim.VirtualMachine.html#relocate
+
+
+History
+=======
+
+.. list-table:: Revisions
+   :header-rows: 1
+
+   * - Release Name
+     - Description
+   * - Newton
+     - Introduced
+   * - Ocata
+     - Reproposed
+   * - Pike
+     - Reproposed
+   * - Queens
+     - Reproposed
+   * - Rocky
+     - Reproposed