[Bug 2015377] Fix merged to neutron (stable/wallaby)

[OpenStack Infra]

Reviewed:  https://review.opendev.org/c/openstack/neutron/+/883535
Committed: https://opendev.org/openstack/neutron/commit/d636685f497f5ca2784f92f5d5b8bd24cf35c170
Submitter: "Zuul (22348)"
Branch:    stable/wallaby

commit d636685f497f5ca2784f92f5d5b8bd24cf35c170
Author: Brian Haley <haleyb.dev at gmail.com>
Date:   Fri Apr 7 17:06:40 2023 -0400

    OVN: Always try and create a metadata port on subnets
    
    When a subnet is updated, for example, to disable then
    re-enable DHCP on it, if there is no metadata port it
    will just return without trying to allocate an IP,
    leaving DHCP unusable on the subnet.  This could happen
    if an admin, even accidentally, deletes the DHCP port
    on a subnet while DHCP is disabled.
    
    This also makes OVN behave like ML2/OVS, which will
    re-create the DHCP port when the enable_dhcp flag is
    changed to false and back to true.
    
    Change-Id: I943f2fb4db9dc33dc372f844d6133faff415befe
    Closes-bug: #2015377
    (cherry picked from commit 267efd298479d66c64d55a76bd21c9664080f76a)
    (cherry picked from commit 0681f8b3ad43aafa6e6af521f2b0aaa5923041a1)
    (cherry picked from commit 47b9511ec5da9b8c8721316f7671bc794c848147)


** Tags added: in-stable-ussuri

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https://bugs.launchpad.net/bugs/2015377

Title:
  [ovn] If dhcp port is deleted from neutron, it is never recreated

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

Bug description:
  This is happening in charmed OpenStack yoga/stable using ovn 22.03.

  Neutron version is 2:20.2.0-0ubuntu1

  If the dhcp port of a subnet is deleted via OpenStack API, this will
  never be recreated even toggling the dhcp on the subnet with:

  openstack subnet set --no-dhcp/--dhcp <uuid>

  This will cause also a missing route for metadata in OVN DHCP_Options:

  i.e.

  _uuid               : 2d4871f5-b675-4978-b291-a1ea7bb5bd4c
  cidr                : "192.168.100.0/24"
  external_ids        : {"neutron:revision_number"="1", subnet_id="62b269e0-6668-48ae-9728-aacd7a99df95"}
  options             : {dns_server="{91.189.91.131, 91.189.91.132}", lease_time="43200", mtu="1500", router="192.168.100.1", server_id="192.168.100.1", server_mac="fa:16:3e:15:13:e6"}

  
  Note the missing classless_static_route="{169.254.169.254/32,192.168.100.2,0.0.0.0/0,192.168.100.1}"

  
  Even if the dhcp port is then recreated manually with device-id ovnmeta-<net-uuid> and device-owner network:distributed, the missing route won't be added to ovn causing VM creation failure. 

  The routes will appear again in OVN DHCP_Options table only when
  updating the subnet host-routes with:

  openstack subnet set --host-route destination=<subnet>,gateway=<ip-
  address> <uuid>

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