openstack/neutron
Code Issues Proposed changes

[OVN] Add documentation about the OVN agent

Browse Source 
Related-Bug: #2017871
Change-Id: Iba24a034edf03da0a6e8c03264d5d1134cf45e56
This commit is contained in:
Rodolfo Alonso Hernandez 2024-01-19 15:09:42 +00:00 committed by Rodolfo Alonso
parent fe31f4fe02
commit 4275aebe68
2 changed files with 76 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
doc/source/ovn/index.rst
View File

@ -13,3 +13,4 @@ OVN Driver
dhcp_opts.rst
ml2ovn_trace.rst
faq/index.rst
ovn_agent.rst

75
doc/source/ovn/ovn_agent.rst Normal file
View File

@ -0,0 +1,75 @@
.. _ovn_agent:
OVN agent
=========
The OVN agent is a service that could be executed in any node running the
ovn-controller service. This agent provides additional functionalities not
provided by OVN; for example, a metadata proxy between the virtual machines
and the Nova metadata service. This agent will replace the need of
the OVN metadata agent.
OVN and OVS database connectivity
---------------------------------
The OVN agent can access the local OVS database where the service is
running. It also has access to the Northbound and Southbound OVN databases. The
connection strings to these databases are defined in the agent configuration
file:
.. code-block:: console
[ovn]
ovn_nb_connection = tcp:192.168.10.100:6641
ovn_sb_connection = tcp:192.168.10.100:6642
[ovs]
ovsdb_connection = tcp:127.0.0.1:6640
Plugable extensions
-------------------
The OVN agent provides functionalities via extensions. When the agent is
started, the ``OVNAgentExtensionManager`` instance loads the configured
extensions. The extensions are defined in the stevedore entry points, under
the section "neutron.agent.ovn.extensions". The extensions are defined in the
agent configuration file in the "extensions" parameter:
.. code-block:: console
[DEFAULT]
extensions = metadata
Each extension will inherit from ``OVNAgentExtension``, which provides the API
for an OVN agent extension. The extensions are loaded in two steps:
* Initialization: this phase involves the call of
``OVNAgentExtension.consume_api`` and ``OVNAgentExtension.initialize`` (in
this order). The first one assigns the extension API to the instance. In this
case, the OVN agent has a specific instance ``OVNAgentExtensionAPI`` that
gives to the extensions the needed access to OVS and OVN databases, using the
same IDL instance. The second one is not currently used in the base class;
it could be used, for example as in the metadata extension, to spawn the
process monitor.
* Start: in this phase, the OVN and OVS database connections are established
and can be accessed. The extension manager will call each extension
``OVNAgentExtension.start`` method.
Each extension should define a set of OVS, OVN Northbound and OVN Southbound
tables to monitor, and a set of events related to these databases. The OVN
agent will create the corresponding IDL connections using the conjunction of
these tables and events.
Event-driven service
--------------------
The OVN agent is a ``oslo_service.service.Service`` type class, that is
launched when the script is executed. Once initialized, the service is waiting
for new events that will trigger actions. As mentioned in the previous section,
each extension will subscribe to a set of events from the OVN and OVS
databases; these events will trigger a set of actions executed on the OVN
agent.