[Bug 1927868] Re: vRouter not working after update to 16.3.1

[Jared Baker]

OK, I did find evidence that this issue did begin to happen as we
upgraded our Train packages just before we upgraded to Ussuri (I believe
its best practice to update all packages, THEN upgrade to a new version
of OpenStack)

Upgraded Neutron 15.3.0 to 15.3.3 at 16:40 EDT
2021-06-10 16:40:40 upgrade neutron-l3-agent:all 2:15.3.0-0ubuntu1~cloud2 2:15.3.3-0ubuntu1~cloud0

Evidence of gateway problems at 17:06 EDT (Might have seen this in the logs several minutes earlier but I had to purge a lot of logs from that day because of the sheer volume of them)
2021-06-10 17:06:23.440 33440 ERROR neutron.agent.l3.ha_router [-] Gateway interface for router 04a5a2c3-739f-4cf6-94bb-dd314c2a8e66 was not set up; router will not work properly

Upgraded from latest Train to latest Ussuri happened at 17:12
2021-06-10 17:12:31 upgrade neutron-l3-agent:all 2:15.3.3-0ubuntu1~cloud0 2:16.3.1-0ubuntu1~cloud0

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Title:
  vRouter not working after update to 16.3.1

Status in neutron:
  New
Status in neutron package in Ubuntu:
  Confirmed

Bug description:
  We run a juju managed Openstack Ussuri on Bionic. After updating
  neutron packages from 16.3.0 to 16.3.1 all virtual routers stopped
  working. It seems that most (not all) namespaces are created but have
  only the lo interface and sometime the ha-XYZ interface in DOWN state.
  The underlying tap interfaces are also in down.

  neutron-l3-agent has many logs similar to the following:
  2021-05-08 15:01:45.286 39411 ERROR neutron.agent.l3.ha_router [-] Gateway interface for router 02945b59-639b-41be-8237-3b7933b4e32d was not set up; router will not work properly

  and journal logs report at around the same time
  May 08 15:01:40 lar1615.srv-louros.grnet.gr neutron-keepalived-state-change[18596]: 2021-05-08 15:01:40.765 18596 INFO neutron.agent.linux.ip_lib [-] Failed sending gratuitous ARP to 62.62.62.62 on qg-5a6efe8c-6b in namespace qrouter-02945b59-639b-41be-8237-3b7933b4e32d: Exit code: 2; Stdin: ; Stdout: Interface "qg-5a6efe8c-6b" is down
  May 08 15:01:40 lar1615.srv-louros.grnet.gr neutron-keepalived-state-change[18596]: 2021-05-08 15:01:40.767 18596 INFO neutron.agent.linux.ip_lib [-] Interface qg-5a6efe8c-6b or address 62.62.62.62 in namespace qrouter-02945b59-639b-41be-8237-3b7933b4e32d was deleted concurrently

  
  The neutron packages installed are:

  ii  neutron-common                         2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - common
  ii  neutron-dhcp-agent                     2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - DHCP agent
  ii  neutron-l3-agent                       2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - l3 agent
  ii  neutron-metadata-agent                 2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - metadata agent
  ii  neutron-metering-agent                 2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - metering agent
  ii  neutron-openvswitch-agent              2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - Open vSwitch plugin agent
  ii  python3-neutron                        2:16.3.1-0ubuntu1~cloud0                                    all          Neutron is a virtual network service for Openstack - Python library
  ii  python3-neutron-lib                    2.3.0-0ubuntu1~cloud0                                       all          Neutron shared routines and utilities - Python 3.x
  ii  python3-neutronclient                  1:7.1.1-0ubuntu1~cloud0                                     all          client API library for Neutron - Python 3.x


  Downgrading to 16.3.0 resolves the issues.

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