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