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[Alan Pevec <1447034@xxxxxxxxxxxxxxxxxx>]

** Also affects: neutron/kilo
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1447034

Title:
  DVR: floating IPs not working if initially associated with non-bound
  port

Status in neutron:
  Fix Committed
Status in neutron kilo series:
  New

Bug description:
  Floating agent gw port is only created for compute host when floating ip is associated with a VM resided on this host [1].
  If associate neutron port with floating ip before booting a VM with that port, floating agent gw port won't be created (in case this is the first VM scheduled to a compute host).
  In that case l3 agent on compute host will receive router info with floating ip but no floating agent gw port: it will subscribe the router for fip namespace [2] but namespace itself won't be created [3]:
   [dvr_router.py]

      def create_dvr_fip_interfaces(self, ex_gw_port):
          floating_ips = self.get_floating_ips()
          fip_agent_port = self.get_floating_agent_gw_interface(
              ex_gw_port['network_id'])
          LOG.debug("FloatingIP agent gateway port received from the plugin: "
                    "%s", fip_agent_port)
          if floating_ips:
              is_first = self.fip_ns.subscribe(self.router_id)
              if is_first and fip_agent_port:
                  if 'subnets' not in fip_agent_port:
                      LOG.error(_LE('Missing subnet/agent_gateway_port'))
                  else:
                      self.fip_ns.create_gateway_port(fip_agent_port)
          ...  


  Since l3 agent already subscribed the router for fip_ns it won't ever
  create fip namespace for that router - this results in floating ips
  not working anymore for ANY subsequent VMs on that compute host, no
  matter if floating ip was associated with a VM or with a non-binded
  port (later associated with a VM).

  I see two possible fixes:
   - add callback for PORT UDATE event to dvr server code to react on port with floating ip being associated with a VM.
  This seems not optimal given lots of checks needed in the callback which will be called fairly often.

   - l3 agent on a compute host should request floating agent gw
  creation by rpc in case it receives router info with floating ips but
  no floating agent gateway. There is already such a method in agent to
  plugin rpc interface which now seems not used anywhere except tests.
  I'm not seeing any cons here so that's what I'm going to propose.

  [1] https://github.com/openstack/neutron/blob/master/neutron/db/l3_dvr_db.py#L214-L225
  [2] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/dvr_router.py#L502
  [3] https://github.com/openstack/neutron/blob/master/neutron/agent/l3/dvr_router.py#L503-L507

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