api-plugin-ovn forcibly overrides charm-neutron-api's default-tenant-network-type

[Nobuto Murata]

charm-neutron-api allows users setting "default-tenant-network-type" which network type should be used by default as a tenant network.
https://jaas.ai/neutron-api#charm-config-default-tenant-network-type

One of the use cases is setting vlan or flat prior to overlay networks such as gre or vxlan. However, by using charm-neutron-api-plugin-ovn, the list in neutron.conf will have "geneve" at the top of the list and it will be used by default.

[when default-tenant-network-type is empty(default) in neutron-api charm config]
tenant_network_types = geneve,gre,vlan,flat,local

[actual value when default-tenant-network-type is vlan]
tenant_network_types = geneve,vlan,gre,flat,local

[expected value when default-tenant-network-type is vlan]
tenant_network_types = vlan,geneve,gre,flat,local

[Nobuto Murata (nobuto)]

default_tenant_network_type is not passed from neutron-api to neutron-api-plugin-ovn.

machine-1-lxd-3: 05:01:52 INFO unit.neutron-api-plugin-ovn/0.juju-log neutron-plugin:59: DEBUG: neutron_config_data="{'core_plugin': 'neutron.plugins.ml2.plugin.Ml2Plugin', 'neutron_security_groups': True, 'tenant_network_types': 'vlan,gre,flat,local', 'restart_trigger': None, 'extension_drivers': 'dns_domain_ports', 'mechanism_drivers': 'openvswitch,hyperv,l2population', 'service_plugins': 'router,metering,segments,neutron_dynamic_routing.services.bgp.bgp_plugin.BgpPlugin'}"

[Alex Kavanagh (ajkavanagh)]

Triaged: High

Confirmed that the ovn plugin doesn't get the default-tenant-network-type and forces 'geneve' as the first item here:

https://github.com/openstack/charm-neutron-api-plugin-ovn/blob/c78ae6f8f307d34a29f9c9b810c7c44205c39e29/src/lib/charm/openstack/neutron_api_plugin_ovn.py#L228

    def tenant_network_types(self, neutron_tenant_network_types=None):
        """Provide list of tenant network types for current OpenStack release.

        The ``network_types`` class variable dfines which types to
        prepend and must be set in the release specific charm classes.

        :param neutron_tenant_network_types: Comma separated list of tenant
                                             network types from Neutron.
        :type neutron_tenant_network_types: Optional[str]
        :returns: List of tenant network types
        :rtype: List[str]
        """
        neutron_tenant_network_types = neutron_tenant_network_types or ''
        return self.network_types + [
            network_type
            for network_type in neutron_tenant_network_types.split(',')
        ]

self.network_types = ['geneve'] as a default.

To fix this, we have to float the default-default-tenant-network-type into the plugin relation-data and then make use of it in the plugin.

[Frode Nordahl (fnordahl)]

I concur with your assessment, Alex.

The way the subordinate plugin framework is laid out in the neutron-api charm the existing helper functions for the NeutronCCContext class does not appear to be used at all when these decisions are outsourced to a subordinate.

So if the plugin subordinate could also get the default-tenant-network-type it could make a better choice.

Note that the reasoning behind the current layout is to always use geneve when OVN is in use as gre and vxlan are not supported.

But the non-overlay types should be fine to use, so allowing the user to choose that through the existing option would be a good way forward.