Duplicate external_ip in NAT table lead to loss of N/S connectivity

[Frode Nordahl]

In a busy CI cloud Neutron appears to leave behind stale NAT records. When this happens a new instance may come around referencing the same external_ip, and the new instance will have connectivity issues.

An example showing this situation:
$ sudo ovn-nbctl list nat|grep -B5 -A5 10.245.165.87

_uuid : 97e89f15-007e-4cf6-865f-9c796e11faf5
allowed_ext_ips : []
exempted_ext_ips : []
external_ids : {"neutron:fip_external_mac"="fa:16:3e:7e:c2:a1", "neutron:fip_id"="be6fa0b0-458c-42a1-b682-a4d6c33982be", "neutron:fip_port_id"="85bf473a-eafe-4ff1-85e3-810cad395295", "neutron:revision_number"="0", "neutron:router_name"=neutron-bfcd42ec-abb3-4a8b-8774-42767cc34cfb}
external_ip : "10.245.165.87"
external_mac : []
external_port_range : ""
logical_ip : "172.16.0.90"
logical_port : "85bf473a-eafe-4ff1-85e3-810cad395295"
options : {}
--

_uuid : 2dc59d66-8866-47d4-a97d-17ee5b8874e2
allowed_ext_ips : []
exempted_ext_ips : []
external_ids : {"neutron:fip_external_mac"="fa:16:3e:28:a6:a8", "neutron:fip_id"="4f9524c6-5b99-45bf-b4bf-8f840231f19e", "neutron:fip_network_id"="5827fa17-882a-4c19-89a8-f6fe4c28d6dd", "neutron:fip_port_id"="08adde8a-60d4-4ed0-b08b-733ba12ad2ce", "neutron:revision_number"="6", "neutron:router_name"=neutron-3824b194-35c2-4511-95c5-2ab5b174c324}
external_ip : "10.245.165.87"
external_mac : []
external_port_range : ""
logical_ip : "10.5.0.26"
logical_port : "08adde8a-60d4-4ed0-b08b-733ba12ad2ce"
options : {stateless="true"}

So the questions then become:
1) Are there anything to de done with the OVN data structure to prevent this from happening.
2) What can Neutron do to not leave these records behind and/or clean them up.