Multiple backend support for L3 routers in ML2/OVN
This spec proposes to support multiple back-ends for routers in the ML2/OVN mechanism driver Partial-Bug: #2020823 Change-Id: Ic7f84d8252ef5197b4d1851f7296e237bf581503
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Miguel Lavalle
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specs/2023.2/ml2ovn-router-flavors.rst
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specs/2023.2/ml2ovn-router-flavors.rst
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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====================================================================
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Flavor/service provider support for routers in the ML2/OVN L3 plugin
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====================================================================
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https://bugs.launchpad.net/neutron/+bug/2020823
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In `Multiple L3 backends`_, functionality was added to the ML2/OVS mechanism
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driver to support L3 routers implemented by different back-end drivers.
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Recently, OpenStack deployers in the Telco / 5G industry have expressed a
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strong interest to have the same support with the ML2/OVN mechanism driver.
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This specification proposes to implement that functionality.
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Problem Description
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===================
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Since early in the development of Neutron, the community recognized the need to
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provide frameworks to enable operators and users of a cloud deployment to
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configure and select from a set of options different implementations of
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services such as VPNs, firewalls, routers, etc. This has led over the years to
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proposals and additions to Neutron such as `Neutron/Service Type Framework`_,
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`Service Flavor Framework`_ and the aforementioned `Multiple L3 backends`_.
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All this is represented in the API by `Networking Flavors Framework`_,
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`Service Providers`_ and the `L3 flavors extension`_.
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As of the writing of this specification, operators using ML2/OVN cannot take
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advantage of all these existing frameworks to offer different implementations
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(flavors from here on) of vrouters to their users. As a consequence, Neutron
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cannot serve a use case where Telco operators want to provide at the same time
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different grades of vrouters, such as:
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* OVN vrouters for their IT / back-office workloads.
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* Specialized vrouters outside OVN for their 5G mobile networks.
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* Specialized vrouters outside OVN for their 4G mobile networks.
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* Other types of specialized vrouters.
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Proposed Change
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===============
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The proposal is to add to the ML2/OVN L3 plugin the ability to process
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different flavors of vrouters. The default flavor will be the native OVN
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vrouter.
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To achieve this, all the OVN specific functionality in the ML2/OVN L3 plugin
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related to vrouters and floating IPs will be refactored to a separate driver.
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Once this is done, the L3 plugin will be responsible for performing only the
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Neutron DB processing steps related to vrouters and floating IPs, while letting
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separate drivers to take care of all the backend processing. These drivers will
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listen and act on events notifications sent by the refactored L3 plugin for the
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creation, update and deletion of vrouters and floating IPs. Each driver will be
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responsible to act only on those events that pertain to its flavor.
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Cloud administrators will configure, load and associate with flavor names
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drivers for backends different to OVN. The following diagram illustrates the
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proposed scenario:
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::
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+--------+ +------------+ +------------+ +------+ +------+ +-----------------+
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| | | | Event | |--->| NBDB |--->| SBDB |--->| OVN Controllers |
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| | | | Notifications | Driver for | +------+ +------+ +-----------------+
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| | | |-------------->| flavor OVN |
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| | | | | |
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| | | | +------------+
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| | | |
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| | | | +------------+ +-----------+
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| | | | Event | |--->| Backend A |
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| ReST | Requests | L3 | Notifications | Driver for | +-----------+
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| API |--------->| plugin |-------------->| flavor A |
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| | | | | |
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| | | | +------------+
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| | | |
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| | | | +------------+ +-----------+
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| | | | Event | |--->| Backend B |
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| | | | Notifications | Driver for | +-----------+
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| | | |-------------->| flavor B |
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| | | | | |
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+--------+ +------------+ +------------+
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| |
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| +-------------+ |
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| | | |
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Updates +------>| Neutron |<------+ Reads
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| database |
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| |
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+-------------+
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In this diagram, backend means any combinations of agents and databases
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(outside the purview of Neutron) that a driver needs to instantiate routers and
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floating IPs in the data plane. This specification implementation will include
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a driver for OVN and the necessary scaffolding to enable other drivers to be
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configured in a Neutron deployment, but the drivers themselves and their
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associated databases and agents will be provided by third parties.
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Once drivers are configured, users will specify the required flavor when
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creating vrouters. The OVN flavor will be the default and will be denoted by
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specifying no flavor in the create request. The following commands illustrate
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how to create a thrid party flavor vrouter:
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::
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$ openstack network flavor list
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+--------------------------------------+----------------------------+---------+---------------+------------------------------------------------------+
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| ID | Name | Enabled | Service Type | Description |
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+--------------------------------------+----------------------------+---------+---------------+------------------------------------------------------+
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| e47c1c5c-629b-4c48-b49a-78abe6ac7696 | user-defined-router-flavor | True | L3_ROUTER_NAT | User defined flavor for routers in the L3 OVN plugin |
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+--------------------------------------+----------------------------+---------+---------------+------------------------------------------------------+
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$ openstack router create router-of-user-defined-flavor --flavor e47c1c5c-629b-4c48-b49a-78abe6ac7696
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+-------------------------+--------------------------------------+
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| Field | Value |
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+-------------------------+--------------------------------------+
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| admin_state_up | UP |
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| availability_zone_hints | |
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| availability_zones | |
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| created_at | 2023-06-08T20:26:01Z |
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| description | |
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| enable_ndp_proxy | None |
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| external_gateway_info | null |
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| flavor_id | e47c1c5c-629b-4c48-b49a-78abe6ac7696 |
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| id | fe110d50-f994-4593-86a4-fc2ecca34c38 |
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| name | router-of-user-defined-flavor |
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| project_id | b807321af03f44dc808ff06bbc845804 |
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| revision_number | 1 |
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| routes | |
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| status | ACTIVE |
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| tags | |
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| tenant_id | b807321af03f44dc808ff06bbc845804 |
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| updated_at | 2023-06-08T20:26:01Z |
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+-------------------------+--------------------------------------+
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As of the writing of this specification, the openstack client doesn't allow the
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specification of a flavor ID when creating a vrouter. Adding this functionality
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to the client will be part of this specification's implementation.
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The OVN flavor driver will be loaded by default when the L3 plugin starts.
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This is an example of the steps a cloud administrator will follow to configure
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and load drivers for other flavors:
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#. Add the service provider to neutron.conf::
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[service_providers]
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service_provider = L3_ROUTER_NAT:user-defined:neutron.services.ovn_l3.service_providers.user_defined.UserDefined
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#. Re-start the neutron server and verify the user defined provider has been
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loaded::
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$ openstack network service provider list
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+---------------+--------------+---------+
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| Service Type | Name | Default |
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+---------------+--------------+---------+
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| L3_ROUTER_NAT | user-defined | False |
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| L3_ROUTER_NAT | ovn | True |
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+---------------+--------------+---------+
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#. Create a service profile for the router flavor::
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$ openstack network flavor profile create --description "User defined router flavor profile" --enable --driver neutron.services.ovn_l3.service_providers.user_defined.UserDefined
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+-------------+--------------------------------------------------------------------+
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| Field | Value |
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+-------------+--------------------------------------------------------------------+
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| description | User defined router flavor profile |
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| driver | neutron.services.ovn_l3.service_providers.user_defined.UserDefined |
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| enabled | True |
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| id | a717c92c-63f7-47e8-9efb-6ad0d61c4875 |
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| meta_info | |
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| project_id | None |
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+-------------+--------------------------------------------------------------------+
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#. Create the router flavor::
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$ openstack network flavor create --service-type L3_ROUTER_NAT --description "User defined flavor for routers in the L3 OVN plugin" user-defined-router-flavor
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+---------------------+------------------------------------------------------+
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| Field | Value |
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+---------------------+------------------------------------------------------+
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| description | User defined flavor for routers in the L3 OVN plugin |
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| enabled | True |
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| id | e47c1c5c-629b-4c48-b49a-78abe6ac7696 |
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| name | user-defined-router-flavor |
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| service_profile_ids | [] |
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| service_type | L3_ROUTER_NAT |
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+---------------------+------------------------------------------------------+
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#. Add service profile to router flavor::
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$ openstack network flavor add profile user-defined-router-flavor a717c92c-63f7-47e8-9efb-6ad0d61c4875
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REST API impact
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---------------
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No REST API impact is expected.
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DB Impact
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---------
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No DB impact is expected.
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Implementation
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==============
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Assignee(s)
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-----------
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* Miguel Lavalle irc: mlavalle, email: mlavalle@redhat.com
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Work Items
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----------
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* Re-factor the OVN vrouters and floating IPs (NAT) functionality embedded in
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the L3 plugin to a separate driver.
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* Implement a drivers controller for the L3 plugin that will load automatically
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the driver for OVN routers and floating IPs.
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* Update the the ML2/OVN maintenance task so vrouters of third party flavors
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are not synched with the NBDB.
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* Add functionality to the openstack client to enable users to specify a flavor
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when creating a vrouter.
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* Implement tests.
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* Write documentation.
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References
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==========
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Provided inline in the text above.
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.. _Multiple L3 backends: https://review.opendev.org/q/topic:bp%252Fmulti-l3-backends
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.. _Neutron/Service Type Framework: https://wiki.openstack.org/wiki/Neutron/ServiceTypeFramework
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.. _Service Flavor Framework: https://specs.openstack.org/openstack/neutron-specs/specs/liberty/neutron-flavor-framework.html
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.. _Networking Flavors Framework: https://docs.openstack.org/api-ref/network/v2/index.html#networking-flavors-framework-v2-0-current-flavor-service-profile
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.. _Service Providers: https://docs.openstack.org/api-ref/network/v2/index.html#service-providers
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.. _L3 flavors extension: https://docs.openstack.org/api-ref/network/v2/index.html#l3-flavors-extension-l3-flavors
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