[Bug 1744062] Re: L3 HA: multiple agents are active at the same time

[LIU Yulong]

VRRP heart beat lose may cause the multiple active router behavior. The
underlying connectivity is key point for this. A monitoring for such
behavior is also necessary.

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https://bugs.launchpad.net/bugs/1744062

Title:
  L3 HA: multiple agents are active at the same time

Status in Ubuntu Cloud Archive:
  Triaged
Status in Ubuntu Cloud Archive mitaka series:
  Triaged
Status in Ubuntu Cloud Archive newton series:
  Triaged
Status in Ubuntu Cloud Archive ocata series:
  Triaged
Status in Ubuntu Cloud Archive pike series:
  Triaged
Status in Ubuntu Cloud Archive queens series:
  Triaged
Status in neutron:
  New
Status in neutron package in Ubuntu:
  Triaged
Status in neutron source package in Xenial:
  Triaged
Status in neutron source package in Artful:
  Triaged
Status in neutron source package in Bionic:
  Triaged

Bug description:
  This is the same issue reported in
  https://bugs.launchpad.net/neutron/+bug/1731595, however that is
  marked as 'Fix Released' and the issue is still occurring and I can't
  change back to 'New' so it seems best to just open a new bug.

  It seems as if this bug surfaces due to load issues. While the fix
  provided by Venkata (https://review.openstack.org/#/c/522641/) should
  help clean things up at the time of l3 agent restart, issues seem to
  come back later down the line in some circumstances. xavpaice
  mentioned he saw multiple routers active at the same time when they
  had 464 routers configured on 3 neutron gateway hosts using L3HA, and
  each router was scheduled to all 3 hosts. However, jhebden mentions
  that things seem stable at the 400 L3HA router mark, and it's worth
  noting this is the same deployment that xavpaice was referring to.

  It seems to me that something is being pushed to it's limit, and
  possibly once that limit is hit, master router advertisements aren't
  being received, causing a new master to be elected. If this is the
  case it would be great to get to the bottom of what resource is
  getting constrained.

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