Comment 25 for bug 1786346

Reviewed: https://review.openstack.org/591735
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bfe89fec4669df6f4ac48dbb56fde3db0a24cbac
Submitter: Zuul
Branch: stable/queens

commit bfe89fec4669df6f4ac48dbb56fde3db0a24cbac
Author: Matt Riedemann <email address hidden>
Date: Fri Mar 30 17:16:08 2018 -0400

    Wait for network-vif-plugged before starting live migration

    This adds a new config option which is read on the source host
    during pre_live_migration which can be used to determine
    if it should wait for a "network-vif-plugged" event due to VIFs
    being plugged on the destination host. This helps us to
    avoid the guest transfer at all if vif plugging failed on the dest
    host, which we just wouldn't find out until post live migration
    and then we have to rollback.

    The option is disabled by default for backward compatibility and
    also because certain networking backends, like OpenDaylight, are
    known to not send network-vif-plugged events unless the port host
    binding information changes, which for live migration doesn't happen
    until after the guest is transferred to the destination host.

    Related to blueprint neutron-new-port-binding-api
    Related-Bug: #1786346

    NOTE(danms): Stable-only changes to this patch from master include
    removing the RPC-related communication from the destination
    to the source node. As such, the new option is read on the source
    node so the conf option help and release note are updated. This is
    OK before Rocky since we don't claim support to live migrate
    between different networking backends (vif types), so operators
    would need to set the option universally, or at least have host
    aggregates in place if they are using different network types.

    Conflicts:
            nova/conf/compute.py
            nova/tests/unit/objects/test_migrate_data.py

    Change-Id: I0f3ab6604d8b79bdb75cf67571e359cfecc039d8
    (cherry picked from commit 5aadff75c3ac4f2019838600df6580481a96db0f)