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[OpenStack Infra <1837635@xxxxxxxxxxxxxxxxxx>]

Reviewed:  https://review.opendev.org/672568
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=3f022a193f66fde3bfd945af1119a60dfe91cb91
Submitter: Zuul
Branch:    master

commit 3f022a193f66fde3bfd945af1119a60dfe91cb91
Author: Rodolfo Alonso Hernandez <ralonsoh@xxxxxxxxxx>
Date:   Wed Jul 24 16:32:02 2019 +0000

    Delay HA router transition from "backup" to "master"
    
    As described in the bug, when a HA router transitions from "master" to
    "backup", "keepalived" processes will set the virtual IP in all other
    HA routers. Each HA router will then advert it and "keepalived" will
    decide, according to a trivial algorithm (higher interface IP), which
    one should be "master". At this point, the other "keepalived" processes
    running in the other servers, will remove the HA router virtual IP
    assigned an instant before
    
    To avoid transitioning some routers form "backup" to "master" and then
    to "backup" in a very short period, this patch delays the "backup" to
    "master" transition, waiting for a possible new "backup" state. If
    during the waiting period (set to the HA VRRP advert time, 2 seconds
    default) to set the HA state to "master", the L3 agent receives a new
    "backup" HA state, the L3 agent does nothing.
    
    Closes-Bug: #1837635
    
    Change-Id: I70037da9cdd0f8448e0af8dd96b4e3f5de5728ad


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

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https://bugs.launchpad.net/bugs/1837635

Title:
  HA router state change from "standby" to "master" should be delayed

Status in neutron:
  Fix Released

Bug description:
  Currently, when a HA state change occurs, the agent execute a series
  of actions [1]: updates the metadata proxy, updates the prefix
  delegation, executed L3 extension "ha_state_change" methods, updates
  the radvd status and notifies this to the server.

  When, in a system with more than two routers (one in "active" mode and
  the others in "standby"), a switch-over is done, the "keepalived"
  process [2] in each "standby" server will set the virtual IP in the HA
  interface and advert it. In case that other router HA interface has
  the same priority (by default in Neutron, the HA instances of the same
  router ID will have the same priority, 50) but higher IP [3], the HA
  interface of this instance will have the VIPs and routes deleted and
  will become "standby" again. E.g.: [4]

  In some cases, we have detected that when the master controller is
  rebooted, the change from "standby" to "master" of the other two
  servers is detected, but the change from "master" to "standby" of the
  server with lower IP (as commented before) is not registered by the
  server, because the Neutron server is still not accessible (the master
  controller was rebooted). This status change, sometimes, is lost. This
  is the situation when both "standby" servers become "master" but the
  "master"-"standby" transition of one of them is lost.

  1) INITIAL STATUS
  (overcloud) [stack@undercloud-0 ~]$ neutron l3-agent-list-hosting-router router
  neutron CLI is deprecated and will be removed in the future. Use openstack CLI instead.
  +--------------------------------------+--------------------------+----------------+-------+----------+
  | id                                   | host                     | admin_state_up | alive | ha_state |
  +--------------------------------------+--------------------------+----------------+-------+----------+
  | 4056cd8e-e062-4f45-bc83-d3eb51905ff5 | controller-0.localdomain | True           | :-)   | standby  |
  | 527d6a6c-8d2e-4796-bbd0-8b41cf365743 | controller-2.localdomain | True           | :-)   | standby  |
  | edbdfc1c-3505-4891-8d00-f3a6308bb1de | controller-1.localdomain | True           | :-)   | active   |
  +--------------------------------------+--------------------------+----------------+-------+----------+

  2) CONTROLLER 1 REBOOTED
  neutron CLI is deprecated and will be removed in the future. Use openstack CLI instead.
  +--------------------------------------+--------------------------+----------------+-------+----------+
  | id                                   | host                     | admin_state_up | alive | ha_state |
  +--------------------------------------+--------------------------+----------------+-------+----------+
  | 4056cd8e-e062-4f45-bc83-d3eb51905ff5 | controller-0.localdomain | True           | :-)   | active   |
  | 527d6a6c-8d2e-4796-bbd0-8b41cf365743 | controller-2.localdomain | True           | :-)   | active   |
  | edbdfc1c-3505-4891-8d00-f3a6308bb1de | controller-1.localdomain | True           | :-)   | standby  |
  +--------------------------------------+--------------------------+----------------+-------+----------+

  
  The aim of this bug is to make public this problem and propose a patch to delay the transition from "standby" to "master" to let keepalived, among all the instances running in the HA servers, to decide which one of them is the "master" server.

  
  [1] https://github.com/openstack/neutron/blob/stable/stein/neutron/agent/l3/ha.py#L115-L134
  [2] https://www.keepalived.org/
  [3] This method is used by keepalived to define which router is predominant and must be master.
  [4] http://paste.openstack.org/show/754760/

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