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[Chris Dent <cdent+lp@xxxxxxxxxxxxx>]

Public bug reported:


It's hard to find a single place in the nova docs where the impact of availability zones (including default) on the capabilities of live or cold migrations is clear

In https://docs.openstack.org/nova/latest/user/aggregates.html
#availability-zones-azs is probably a good place to describe what's
going on. Some of the rules are discussed in IRC at

http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-
nova.2019-04-03.log.html#t2019-04-03T15:22:39

The gist is that when a server is created, if it is created in an AZ
(either an explicit one, or in the default 'nova' zone) it is required
to stay in that AZ for all move operations unless there is a force,
which can happen in a live migrate or evacuate.

(Caveats abound in this area, see the IRC log for more discussion which
may help to flavor the docs being created.)

The reasoning for this, as far as I can tell, is that requesting an AZ
is a part of the boot constraints and we don't want the moved server to
be in violation of its own constraints.

** Affects: nova
     Importance: Medium
     Assignee: Matt Riedemann (mriedem)
         Status: Confirmed


** Tags: doc docs

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https://bugs.launchpad.net/bugs/1823043

Title:
  Docs insufficiently clear on the intersection of availalability zones,
  force, and cold and live migrations

Status in OpenStack Compute (nova):
  Confirmed

Bug description:
  
  It's hard to find a single place in the nova docs where the impact of availability zones (including default) on the capabilities of live or cold migrations is clear

  In https://docs.openstack.org/nova/latest/user/aggregates.html
  #availability-zones-azs is probably a good place to describe what's
  going on. Some of the rules are discussed in IRC at

  http://eavesdrop.openstack.org/irclogs/%23openstack-nova/%23openstack-
  nova.2019-04-03.log.html#t2019-04-03T15:22:39

  The gist is that when a server is created, if it is created in an AZ
  (either an explicit one, or in the default 'nova' zone) it is required
  to stay in that AZ for all move operations unless there is a force,
  which can happen in a live migrate or evacuate.

  (Caveats abound in this area, see the IRC log for more discussion
  which may help to flavor the docs being created.)

  The reasoning for this, as far as I can tell, is that requesting an AZ
  is a part of the boot constraints and we don't want the moved server
  to be in violation of its own constraints.

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