Send "update" instead of "remove" notification for dvr rescheduling

[Kailun Qin]

Currently, the normal method to reschedule a router is to send a "removed" notification to the old l3 agent followed by an "added" notification targeting the new agent.

However for DVR, this is too harsh as the old agent may still need to keep the router in a non-master role to service any VM ports that exist on that host while the new agent handles the master role of the router (i.e., the centralized components of the router). Besides, the current implementation in remove_router_from_l3_agent also verifies if there are DVR serviceable ports owned by this agent. If so, then the router should be retained.

The same mechanism should be aligned and applied to dvr rescheduling as well.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/581658

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/581658
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=8b16b53b5b54b2ad8521b6c6c22660fab30e1b0d
Submitter: Zuul
Branch: master

commit 8b16b53b5b54b2ad8521b6c6c22660fab30e1b0d
Author: Kailun Qin <email address hidden>
Date: Thu Jul 12 03:18:23 2018 +0800

    Send update instead of remove for DVR reschedule

    The current "agent remove-add" method to reschedule a router is not
    friendly for DVR. In DVR cases, the old agent may still need to keep the
    router in a non-master role to service any VM ports that exit on that
    host while the new agent handles the master role of the router.

    This patch proposes to send "update" instead of "remove" notification
    for DVR rescheduling, which aligns with the retain_router check in
    remove_router_from_l3_agent as well.

    Closes-Bug: #1781179
    Change-Id: I23431f9f46f72e6bce91f3d1fb0ed328d55930fb

[Kailun Qin (kailun.qin)]

Remove the RFE tag from the bug title based on the Bug deputy report 07/10/2018 - 07/16/2018.

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 13.0.0.0b3 development milestone.