OVN: Metadata is not provisioned for a network with DHCP turned off

[Max Khon]

Can be related to #1918914

Openstack version: Ussuri

I have a very simple deployment with a single flat provider network (not sure it matters) with a subnet with DHCP turned off (instances are created only with this network).

In this case neutron-ovn-metadata-agent does not provision metadata service for this network:

---
root@eq-os1:~# ovn-sbctl find Port_Binding type=localport
_uuid : b6329cbe-e80f-48a3-921d-e1031afd85d8
chassis : []
datapath : 097732e0-85d1-4744-a9c6-bafa0d861700
encap : []
external_ids : {"neutron:cidrs"="", "neutron:device_id"=ovnmeta-81954d74-51e6-4598-b6b6-3da3832f20df, "neutron:device_owner"="network:dhcp", "neutron:network_name"=neutron-81954d74-51e6-4598-b6b6-3da3832f20df, "neutron:port_name"="", "neutron:project_id"=f11221fbfbb844209cd49c7ca3a12a00, "neutron:revision_number"="1", "neutron:security_group_ids"=""}
gateway_chassis : []
ha_chassis_group : []
logical_port : "a557f47a-dae7-4150-96c2-71abbf48b84b"
mac : ["fa:16:3e:06:ed:9b"]
nat_addresses : []
options : {requested-chassis=""}
parent_port : []
tag : []
tunnel_key : 2
type : localport
virtual_parent : []
root@eq-os1:~#
---

The reason is that external_ids:neutron:cidrs is empty so provision_datapath() ignores this network in this case:

--- neutron/agent/ovn/metadata/agent.py ---
        # If there's no metadata port or it doesn't have a MAC or IP
        # addresses, then tear the namespace down if needed. This might happen
        # when there are no subnets yet created so metadata port doesn't have
        # an IP address.
        if not (port and port.mac and
                port.external_ids.get(ovn_const.OVN_CIDRS_EXT_ID_KEY, None)):
            LOG.debug("There is no metadata port for network %s or it has no "
                      "MAC or IP addresses configured, tearing the namespace "
                      "down if needed", net_name)
            self.teardown_datapath(datapath, net_name)
            return
---

When DHCP is enabled neutron:cidrs gets not empty and metadata is properly provisioned.

[Brian Haley (brian-haley)]

As you mentioned, this might be related to https://bugs.launchpad.net/neutron/+bug/1918914 - as there is no DHCP port in either case. Since Rodolfo responded in the other one let's see if he responds there to your recent comment.

[Rodolfo Alonso (rodolfo-alonso-hernandez)]

Hello Max:

If any of the subnets of a network have DHCP capabilities, the metadata port of this network namespace will have no IP assigned (exactly the OVN metadata code you are pointing [1]). That means we can't provide the metadata via the metadata IP. You need to use a config-drive in this case [2].

Regards.

[1]https://github.com/openstack/neutron/blob/09207ba731bfc859c2f6d175588a8bfe09be01db/neutron/agent/ovn/metadata/agent.py#L431-L437
[2]https://docs.openstack.org/nova/latest/admin/config-drive.html