[Bug 1759971] Fix proposed to neutron (stable/pike)

[OpenStack Infra]

Fix proposed to branch: stable/pike
Review: https://review.openstack.org/559496

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https://bugs.launchpad.net/bugs/1759971

Title:
  [dvr][fast-exit] a route to a tenant network does not get created in
  fip namespace if an external network is attached after a tenant
  network have been attached (race condition)

Status in neutron:
  Fix Released
Status in neutron package in Ubuntu:
  New

Bug description:
  Overall, similar scenario to
  https://bugs.launchpad.net/neutron/+bug/1759956 but a different
  problem.

  Relevant agent config options:
  http://paste.openstack.org/show/718418/

  OpenStack Queens from UCA (xenial, GA kernel, deployed via OpenStack
  charms), 2 external subnets (one routed provider network), 1 tenant
  subnet, all subnets in the same address scope to trigger "fast exit"
  logic.

  Tenant subnet cidr: 192.168.100.0/24

  openstack address scope create dev
  openstack subnet pool create --address-scope dev --pool-prefix 10.232.40.0/21 --pool-prefix 10.232.16.0/21 dev
  openstack subnet pool create --address-scope dev --pool-prefix 192.168.100.0/24 tenant
  openstack network create --external --provider-physical-network physnet1 --provider-network-type flat pubnet
  openstack network segment set --name segment1 d8391bfb-4466-4a45-972c-45ffcec9f6bc
  openstack network segment create --physical-network physnet2 --network-type flat --network pubnet segment2
  openstack subnet create --no-dhcp --subnet-pool dev --subnet-range 10.232.16.0/21 --allocation-pool start=10.232.17.0,end=10.232.17.255 --dns-nameserver 10.232.36.101 --ip-version 4 --network pubnet --network-segment segment1 pubsubnetl1
  openstack subnet create --gateway 10.232.40.100 --no-dhcp --subnet-pool dev --subnet-range 10.232.40.0/21 --allocation-pool start=10.232.41.0,end=10.232.41.255 --dns-nameserver 10.232.36.101 --ip-version 4 --network pubnet --network-segment segment2 pubsubnetl2
  openstack network create --internal --provider-network-type vxlan tenantnet
   openstack subnet create --dhcp --ip-version 4 --subnet-range 192.168.100.0/24 --subnet-pool tenant --dns-nameserver 10.232.36.101 --network tenantnet tenantsubnet

  # -------
  # Works in this order when an external network is attached first

  openstack router create --disable --no-ha --distributed pubrouter
  openstack router set --disable-snat --external-gateway pubnet --enable pubrouter

  openstack router add subnet pubrouter tenantsubnet

  2018-03-29 23:30:48.933 2050638 DEBUG neutron.agent.linux.utils [-] Running command: ['sudo', 'neutron-rootwrap', '/etc/neutron/rootwrap.conf', 'ip', 'ne
  tns', 'exec', 'fip-d0f008fc-dc45-4237-9ce0-a9e1977735eb', 'ip', '-4', 'route', 'replace', '192.168.100.0/24', 'via', '169.254.106.114', 'dev', 'fpr-09fd1
  424-7'] create_process /usr/lib/python2.7/dist-packages/neutron/agent/linux/utils.py:92

  # ------
  # Doesn't work the other way around - as a fip namespace does not get created before a tenant network is attached
  openstack router create --disable --no-ha --distributed pubrouter

  openstack router add subnet pubrouter tenantsubnet
  openstack router set --disable-snat --external-gateway pubnet --enable pubrouter

  # to "fix" this we need to re-trigger the right code path

  openstack router remove subnet pubrouter tenantsubnet
  openstack router add subnet pubrouter tenantsubnet

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