neutron/releasenotes/notes/ovn-metadata_workers-1121334593ce9829.yaml
Lucas Alvares Gomes f3a8e1547d [OVN][OVS] Different metadata_workers default based on driver
Both drivers have different approaches when it comes to the metatada
agent, for one the metadata agent for ML2/OVN runs on the compute nodes
(it's distributed) instead of the controller nodes.

The previous default of "<# of CPUs> / 2" did not make sense for ML2/OVN
and if left unchanged could result in scalation problems because of the
number of connections to the OVSDB Southbound database, as seeing in
this email thread for example [0].

This patch puts a placeholder value (None) on the default field of
the "metadata_workers" config by not setting it immediately and then
conditionally set the default value based on each driver:

* ML2/OVS defaults to <# CPUs> // 2, as before.
* ML2/OVN defaults to 2, as suggested in the bug description and also
  what's default in TripleO for the OVN driver.

[0]
http://lists.openstack.org/pipermail/openstack-discuss/2020-September/016960.html

Change-Id: I60d5dfef38dc130b47668604c04299b9d23b59b6
Closes-Bug: #1893656
Signed-off-by: Lucas Alvares Gomes <lucasagomes@gmail.com>
2020-09-09 09:39:13 +01:00

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YAML

---
upgrade:
- |
The default value for the ``metadata_workers`` configuration option
has changed to 2 for the ML2/OVN driver. For ML2/OVS the default
value remains the same. Each driver has different approaches when
serving metadata to the instances and the previous default value of
"<number of CPUs> / 2" did not make sense for ML2/OVN as the OVN
metadata agents are distributed running on Compute nodes instead of
Controller nodes. In fact, the previous default value could cause
scalability issues with ML2/OVN and was overwritten by the deployment
tools to avoid problems.