[Bug 1871850] Re: [L3] existing router resources are partial deleted unexpectedly when MQ is gone

[Chris MacNaughton]

** Also affects: cloud-archive/queens
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/rocky
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/ussuri
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/train
   Importance: Undecided
       Status: New

** Also affects: cloud-archive/stein
   Importance: Undecided
       Status: New

** Changed in: cloud-archive/stein
       Status: New => Fix Released

** Changed in: cloud-archive/train
       Status: New => Fix Released

** Changed in: cloud-archive/ussuri
       Status: New => Fix Released

** Changed in: cloud-archive
       Status: New => Invalid

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https://bugs.launchpad.net/bugs/1871850

Title:
  [L3] existing router resources are partial deleted unexpectedly when
  MQ is gone

Status in Ubuntu Cloud Archive:
  Invalid
Status in Ubuntu Cloud Archive queens series:
  New
Status in Ubuntu Cloud Archive rocky series:
  New
Status in Ubuntu Cloud Archive stein series:
  Fix Released
Status in Ubuntu Cloud Archive train series:
  Fix Released
Status in Ubuntu Cloud Archive ussuri series:
  Fix Released
Status in neutron:
  Fix Released

Bug description:
  ENV: meet this issue on our stable/queens deployment, but master
  branch has the same code logic

  When the L3 agent get a router update notification, it will try to
  retrieve the router info from DB server [1]. But at this time, if the
  message queue is down/unreachable. It will get exceptions related
  message queue. A resync action will be run then [2]. Sometimes, from
  my personal experience, rabbitMQ cluster is not so much easy to
  recover. Long time MQ recover time will cause the router info sync RPC
  never get successful until it meets the max retry time [3]. So the bad
  thing happens, L3 agent is trying to remove the router now [4]. It
  basically shutdown all the existing L3 traffic of this router.

  [1] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/agent.py#L705
  [2] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/agent.py#L710
  [3] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/agent.py#L666
  [4] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/agent.py#L671

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