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Merge "Update Availability zone doc page"

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Zuul 2023-01-17 00:06:18 +00:00 committed by Gerrit Code Review
parent d6d8db0c9f b65a910834
commit 668d4e590f
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doc/source/admin/availability-zones.rst
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@ -118,11 +118,47 @@ Implications for moving servers
There are several ways to move a server to another host: evacuate, resize,
cold migrate, live migrate, and unshelve. Move operations typically go through
the scheduler to pick the target host *unless* a target host is specified and
the request forces the server to that host by bypassing the scheduler. Only
evacuate and live migrate can forcefully bypass the scheduler and move a
server to a specified host and even then it is highly recommended to *not*
force and bypass the scheduler.
the scheduler to pick the target host.
Prior to API microversion 2.68, using older openstackclient (pre-5.5.0) and
novaclient, it was possible to specify a target host and the request forces
the server to that host by bypassing the scheduler. Only evacuate and live
migrate can forcefully bypass the scheduler and move a server to specified host
and even then it is highly recommended to *not* force and bypass a scheduler.
- live migrate with force host (works with older openstackclients(pre-5.5.0):
.. code-block:: console
$ openstack server migrate --live <host> <server>
- live migrate without forcing:
.. code-block:: console
$ openstack server migrate --live-migration --host <host> <server>
While support for 'server evacuate' command to openstackclient was added
in 5.5.3 and there it never exposed ability to force an evacuation, but
it was previously possible with novaclient.
- evacuate with force host:
.. code-block:: console
$ nova evacuate --force <server> <host>
- evacuate without forcing using novaclient:
.. code-block:: console
$ nova evacuate
- evacuate without forcing using openstackclient:
.. code-block:: console
$ openstack server evacuate --host <host> <server>
With respect to availability zones, a server is restricted to a zone if:
@ -150,16 +186,6 @@ If the server was not created in a specific zone then it is free to be moved
to other zones, i.e. the :ref:`AvailabilityZoneFilter <AvailabilityZoneFilter>`
is a no-op.
Knowing this, it is dangerous to force a server to another host with evacuate
or live migrate if the server is restricted to a zone and is then forced to
move to a host in another zone, because that will create an inconsistency in
the internal tracking of where that server should live and may require manually
updating the database for that server. For example, if a user creates a server
in zone A and then the admin force live migrates the server to zone B, and then
the user resizes the server, the scheduler will try to move it back to zone A
which may or may not work, e.g. if the admin deleted or renamed zone A in the
interim.
Resource affinity
~~~~~~~~~~~~~~~~~