..
      Licensed under the Apache License, Version 2.0 (the "License"); you may
      not use this file except in compliance with the License. You may obtain
      a copy of the License at

          http://www.apache.org/licenses/LICENSE-2.0

      Unless required by applicable law or agreed to in writing, software
      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
      License for the specific language governing permissions and limitations
      under the License.


      Convention for heading levels in Neutron devref:
      =======  Heading 0 (reserved for the title in a document)
      -------  Heading 1
      ~~~~~~~  Heading 2
      +++++++  Heading 3
      '''''''  Heading 4
      (Avoid deeper levels because they do not render well.)


Service Extensions
==================

Historically, Neutron supported the following advanced services:

#. **FWaaS** (*Firewall-as-a-Service*): runs as part of the L3 agent.
#. **LBaaS** (*Load-Balancer-as-a-Service*): implemented purely inside
   neutron-server, does not interact directly with agents.
#. **VPNaaS** (*VPN-as-a-Service*): derives from L3 agent to add
   VPNaaS functionality.

Starting with the Kilo release, these services are split into separate
repositories, and more extensions are being developed as well. Service
plugins are a clean way of adding functionality in a cohesive manner
and yet, keeping them decoupled from the guts of the framework. The
aforementioned features are developed as extensions (also known as
service plugins), and more capabilities are being added to Neutron
following the same pattern. For those that are deemed 'orthogonal'
to any network service (e.g. tags, timestamps, auto_allocate, etc),
there is an informal `mechanism <https://github.com/openstack/neutron/blob/aadf2f30f84dff3d85f380a7ff4e16dbbb0c6bb0/neutron/plugins/common/constants.py#L41>`_
to have these loaded automatically at server startup. If you
consider adding an entry to the dictionary, please be kind and
reach out to your PTL or a member of the drivers team for approval.

#. http://git.openstack.org/cgit/openstack/neutron-fwaas/
#. http://git.openstack.org/cgit/openstack/neutron-lbaas/
#. http://git.openstack.org/cgit/openstack/neutron-vpnaas/

