Submitter: Zuul
Branch:    master

commit 8d68f2323040908008fcd023a40f7fadf5641e59
Author: Matt Riedemann <>
Date:   Sun Mar 25 16:56:19 2018 -0400

    Avoid unnecessary port update during live migration
    The ComputeManager.pre_live_migration method, which runs on the
    destination host during live migration, calls setup_networks_on_host
    with the destination host which causes the "migrating_to" attribute
    to get set to the destination host in the port binding profile. This
    is to initiate setting up floating IP information on the destination
    host for DVR.
    The ComputeManager.post_live_migration_at_destination method calls the
    same method from the destination host, so at this point the "migrating_to"
    attribute is already set to the destination host in the port binding
    profile from pre_live_migration and we make unnecessary port update calls
    to Neutron for each port attached to the instance.
    This change simply checks to see if the "migrating_to" attribute is
    already set to the given host and if so, skips the port update call.
    Change-Id: I8b2ffd94c5ff0881d0df4efdde9be938888c16d7
    Closes-Bug: #1758453

** Changed in: nova
       Status: In Progress => Fix Released

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  Port binding 'migrating_to' attribute needlessly updated in post-live-
  migration for neutron

Status in OpenStack Compute (nova):
  Fix Released

Bug description:
  During live migration, the setup_networks_on_host neutronv2 API method
  checks to see if the provided host is different from the existing and if so, it knows the instance is being migrated and
  sets the 'migrating_to' attribute to the new host in the ports binding

  And then updates the port.

  That happens in pre_live_migration which runs on the dest host:

  And it also happens again in post_live_migration_at_destination which
  runs on the destination host:

  Since the neutronv2 API code doesn't check to see if the
  'migrating_to' attribute is already set:

  It does a redundant PUT (port update) for no actual change.

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