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3.3 KiB
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79 lines
3.3 KiB
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..
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Licensed under the Apache License, Version 2.0 (the "License"); you may
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not use this file except in compliance with the License. You may obtain
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a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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License for the specific language governing permissions and limitations
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under the License.
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Convention for heading levels in Neutron devref:
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======= Heading 0 (reserved for the title in a document)
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------- Heading 1
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~~~~~~~ Heading 2
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+++++++ Heading 3
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''''''' Heading 4
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(Avoid deeper levels because they do not render well.)
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Service Extensions
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==================
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Historically, Neutron supported the following advanced services:
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#. **FWaaS** (*Firewall-as-a-Service*): runs as part of the L3 agent.
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#. **VPNaaS** (*VPN-as-a-Service*): derives from L3 agent to add
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VPNaaS functionality.
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Starting with the Kilo release, these services are split into separate
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repositories, and more extensions are being developed as well. Service
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plugins are a clean way of adding functionality in a cohesive manner
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and yet, keeping them decoupled from the guts of the framework. The
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aforementioned features are developed as extensions (also known as
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service plugins), and more capabilities are being added to Neutron
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following the same pattern. For those that are deemed 'orthogonal'
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to any network service (e.g. tags, timestamps, auto_allocate, etc),
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there is an informal `mechanism <https://github.com/openstack/neutron/blob/aadf2f30f84dff3d85f380a7ff4e16dbbb0c6bb0/neutron/plugins/common/constants.py#L41>`_
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to have these loaded automatically at server startup. If you
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consider adding an entry to the dictionary, please be kind and
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reach out to your PTL or a member of the drivers team for approval.
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#. http://opendev.org/openstack/neutron-fwaas/
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#. http://opendev.org/openstack/neutron-vpnaas/
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Calling the Core Plugin from Services
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-------------------------------------
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There are many cases where a service may want to create a resource
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managed by the core plugin (e.g. ports, networks, subnets). This
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can be achieved by importing the plugins directory and getting a direct
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reference to the core plugin:
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.. code:: python
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from neutron_lib.plugins import directory
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plugin = directory.get_plugin()
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plugin.create_port(context, port_dict)
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However, there is an important caveat. Calls to the core plugin in
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almost every case should not be made inside of an ongoing transaction.
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This is because many plugins (including ML2), can be configured to
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make calls to a backend after creating or modifying an object. If
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the call is made inside of a transaction and the transaction is
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rolled back after the core plugin call, the backend will not be
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notified that the change was undone. This will lead to consistency
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errors between the core plugin and its configured backend(s).
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ML2 has a guard against certain methods being called with an active
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DB transaction to help prevent developers from accidentally making
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this mistake. It will raise an error that says explicitly that the
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method should not be called within a transaction.
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