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[OVN] Document the OVN L3 scheduler: AZs distribution 

This new section describes how the OVN L3 schedulers distribute
the ``Chassis`` candidate list among the Available Zones, in
order to provide more resilience to the L3 HA: if the active
LRP binding fails, the next in the list will belong to another
AZ.

Related-Bug: #2030741
Change-Id: I20aaeefb33c424dc1a9c13f94f2912d0fa973166
This commit is contained in:
Rodolfo Alonso Hernandez 2024-01-21 08:42:45 +00:00 committed by Rodolfo Alonso
parent 188fe6c953
commit df24fbeb48
1 changed files with 19 additions and 0 deletions
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doc/source/admin/ovn/l3_scheduler.rst
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@ -81,8 +81,27 @@ is changed, the ``Logical_Router_Port`` is bound to the new ``Chassis`` and
could break any active sessions.
Availability Zones (AZ) distribution
------------------------------------
Both the ``OVNGatewayChanceScheduler`` and the
``OVNGatewayLeastLoadedScheduler`` schedulers have the Availability Zones (AZ)
in consideration. If a router has any AZ defined, the schedulers will select
only those chassis located in the AZs. If no chassis meets this condition, the
``Logical_Router_Port`` will be assigned to the "neutron-ovn-invalid-chassis".
Once the list of candidate ``Chassis`` (depending on the scheduler selected)
is created, this list is reordered to prioritize these ``Chassis`` from
different AZs. That will spread the allocation choices to all AZs; if the
current (and highest) ``Chassis`` binding fails, the next ``Chassis`` in the
list will belong to another AZ.
This improvement was implemented in [3]_.
References
----------
.. [1] https://review.opendev.org/c/openstack/neutron/+/893653
.. [2] https://review.opendev.org/c/openstack/neutron/+/893654
.. [3] https://review.opendev.org/c/openstack/neutron/+/892604