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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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 has recognized the
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need to provide frameworks to enable operators and users of a cloud deployment
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to 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 framworks to offer different implementations
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(flavors from here on) of routers. As a consequence, Neutron cannot serve a use
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case where Telco operators want to provide different grades of vrouters, such
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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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will be refactored to a separate driver. Once this is done, the L3 plugin will
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be responsible for performing only the Neutron DB processing steps related to
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vrouters and floating IPs, while letting separate drivers to take care of all
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the backend processing. Users will configure, load and associate with flavor
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names drivers for backends different to OVN. The following diagram illustrates
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the proposed scenario:
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::
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+--------+ +------------+ +------------+ +------+ +------+ +----------------+
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| | | | Event | |--->| NBDB |--->| SBDB |--->| OVN Controller |
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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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| databse |
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| |
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+-------------+
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Based on this diagram, the following gives more details on the proposed
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implementation:
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* Users will specify the required flavor when creating vrouters. The OVN flavor
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will be the default and will be denoted by specifying no flavor in the create
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request. The following command illustrates how to create a non-OVN flavor
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router:
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* The OVN driver will be loaded automatically by a drivers controller that will
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be implemented by the work related to this specification
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* The following commands illustrate an example cloud administrator workflow to
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to configure a router flavor:
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* Maintenace job
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* What is meant by backend
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* Drivers listen to events and they decide whether the request is for their
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flavor. The required events already exist.
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* Handling of user defined drivers backends is out of scope
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* Backend may mean DB and agents to setup the data plane
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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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