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[OpenStack Infra <1832028@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/644881
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=19f9b37721d9bc13bc1ed35a4f368b1d21b10a5b
Submitter: Zuul
Branch:    master

commit 19f9b37721d9bc13bc1ed35a4f368b1d21b10a5b
Author: Artom Lifshitz <alifshit@xxxxxxxxxx>
Date:   Wed Mar 20 10:38:12 2019 -0400

    Revert resize: wait for events according to hybrid plug
    
    Since 4817165fc5938a553fafa1a69c6086f9ebe311af, when reverting a
    resized instance back to the source host, the libvirt driver waits for
    vif-plugged events when spawning the instance. When called from
    finish_revert_resize() in the source compute manager, libvirt's
    finish_revert_migration() does not pass vifs_already_plugged to
    _create_domain_and_network(), making the latter use the default False
    value.
    
    When the source compute manager calls
    network_api.migrate_instance_finish() in finish_revert_resize(), this
    updates the port binding back to the source host. If Neutron is
    configured to use OVS hybrid plug, it will send the vif-plugged event
    immediately after completing this request. This happens before the
    virt driver's finish_revert_migration() method is called. This causes
    the wait in the libvirt driver to time out because the event is
    received before Nova starts waiting for it.
    
    The neutron ovs l2 agent sends vif-plugged events when two conditions
    are met. First the port must be bound to the host managed by the
    l2 agent and second, the agent must have completed configuring the
    port on ovs. This involves assigning the port a local VLAN for tenant
    isolation, applying security group rules if required and applying
    QoS policies or other agent extensions like service function chaining.
    
    During the boot process, we bind the port first to the host
    then plug the interface into ovs which triggers the l2 agent to
    configure it resulting in the emission of the vif-plugged event.
    In the revert case, as noted above, since the vif is already plugged
    on the source node when hybrid-plug is used, binding the port to the
    source node fulfils the second condition to send the vif-plugged event.
    
    Events sent immediately after port binding update are hereafter known
    as "bind-time" events. For ports that do not use OVS hybrid plug,
    Neutron will continue to send vif-plugged events only when Nova
    actually plugs the VIF. These types of events are hereafter known as
    "plug-time" events. OVS hybrid plug is a per agent setting, so for
    a particular host, bind-time events are an all-or-nothing thing for the
    ovs backend: either all VIF_TYPE=ovs ports have them, or no ovs ports
    have them. In general, a host will only have one network backend.
    The only exception to this is SR-IOV. SR-IOV is commonly deployed on
    the same host as other network backends such as OVS or linuxbridge.
    SR-IOV ports with VNIC_TYPE=direct-physical will always have only
    bind-time events. If an instance mixes OVS ports with hybrid-plug=False
    with direct physical ports, it will have both kinds of events.
    
    This patch adds functions to the NetworkInfo model that return what
    kinds of events each VIF has. These are then used in the migration
    revert logic to decide when to wait for external events: in the
    compute manager, when binding the port, for bind-time events,
    and/or in libvirt, when plugging the VIFs, for plug-time events.
    
    Closes-bug: 1832028
    Co-Authored-By: Sean Mooney work@xxxxxxxxxxxxxxx
    Change-Id: I51cdcae67be8c68a55bc939de4ea0aba2361dcc4


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

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https://bugs.launchpad.net/bugs/1832028

Title:
  revert resize: vif-plugged external event sent too soon if Neutron is
  using OVS hybrid plug

Status in OpenStack Compute (nova):
  Fix Released
Status in OpenStack Compute (nova) rocky series:
  Confirmed
Status in OpenStack Compute (nova) stein series:
  Confirmed

Bug description:
  Description
  ===========

  This is all only when Neutron is using OVS with hybrid plugging.

  When reverting a resized instance back to its original source host,
  Nova will timeout waiting for the vif-plugged external event, and
  never finish the revert. This happens because the event is sent by
  Neutron as soon as Nova updates the port binding to point back to the
  original source. This happens before the virt driver gets ready to
  listen for external events, so the event arrives, just too soon, and
  Nova times out.

  Steps to reproduce
  ==================

  1. Resize an instance
  2. When it's in VERIFY_RESIZE, revert it

  Expected result
  ===============

  Instance reverts correctly.

  Actual result
  =============

  Instance goes to ERROR.

  Environment
  ===========

  OVS with hybrid plug. Reported in OSP14/Rocky [1], reproduced on
  master [2] [3].

  [1] https://bugzilla.redhat.com/show_bug.cgi?id=1678681
  [2] https://review.opendev.org/#/c/660782/
  [3] https://review.opendev.org/#/c/653498/

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