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devref: added guidelines to maintain service entry points 

Change-Id: I56b3ec90045f50ba707c0b32f8ec00925dbff644
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Ihar Hrachyshka 2015-02-19 17:56:42 +01:00
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doc/source/devref/index.rst
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@ -38,6 +38,7 @@ Neutron Internals
.. toctree::
:maxdepth: 3
services_and_agents
api_layer
api_extensions
plugin-api

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doc/source/devref/services_and_agents.rst Normal file
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Services and agents
===================
A usual Neutron setup consists of multiple services and agents running on one
or multiple nodes (though some exotic setups potentially may not need any
agents). Each of those services provides some of the networking or API
services. Among those of special interest:
#. neutron-server that provides API endpoints and serves as a single point of
access to the database. It usually runs on nodes called Controllers.
#. Layer2 agent that can utilize Open vSwitch, Linuxbridge or other vendor
specific technology to provide network segmentation and isolation for tenant
networks. The L2 agent should run on every node where it is deemed
responsible for wiring and securing virtual interfaces (usually both Compute
and Network nodes).
#. Layer3 agent that runs on Network node and provides East-West and
North-South routing plus some advanced services such as FWaaS or VPNaaS.
For the purpose of this document, we call all services, servers and agents that
run on any node as just "services".
Entry points
------------
Entry points for services are defined in setup.cfg under "console_scripts"
section. Those entry points should generally point to main() functions located
under neutron/cmd/... path.
Note: some existing vendor/plugin agents still maintain their entry points in
other locations. Developers responsible for those agents are welcome to apply
the guideline above.
Interacting with Eventlet
-------------------------
Neutron extensively utilizes the eventlet library to provide asynchronous
concurrency model to its services. To utilize it correctly, the following
should be kept in mind.
If a service utilizes the eventlet library, then it should not call
eventlet.monkey_patch() directly but instead maintain its entry point main()
function under neutron/cmd/eventlet/... If that is the case, the standard
Python library will be automatically patched for the service on entry point
import (monkey patching is done inside `python package file
<http://git.openstack.org/cgit/openstack/neutron/tree/neutron/cmd/eventlet/__init__.py>`_).
Note: an entry point 'main()' function may just be an indirection to a real
callable located elsewhere, as is done for reference services such as DHCP, L3
and the neutron-server.
For more info on the rationale behind the code tree setup, see `the
corresponding cross-project spec <https://review.openstack.org/154642>`_.