[OVN] Stop using neutron.api.rpc.handlers.resources_rpc with OVN as a backend

[Maciej Jozefczyk]

I noticed that in devstack master we have a lot of logs like:

Jul 21 08:18:13.371897 ubuntu-bionic-rax-iad-0018525571 neutron-server[6599]: DEBUG neutron.api.rpc.handlers.resources_rpc [None req-968a9155-c80a-4fbc-9c10-bcfca6ba372d None None] Pushing event updated for resources: {'Port': ['ID=fedef62e-0a31-4136-a693-4b4d3bab289e,revision_number=5']} {{(pid=6988) push /opt/stack/neutron/neutron/api/rpc/handlers/resources_rpc.py:243}}

That means we're pushing resources updates via RPC, but it is not needed with OVN as a backend, because there is no consumer of those messages.

Lets try to stop doing it.

[Akihiro Motoki (amotoki)]

Disabling RPC notification with OVN makes sense.
resources_rpc.ResourcesPushRpcApi is instantiated in the ML2 plugin. It looks like we need some mechanism to determine whether RPC notification is required based on mechanism driver(s) currently enabled.
In addition, some service plugins use resources_rpc.ResourcesPushRpcApi too and some of them assume RPC notification. They also need to be clean up.

[yatin (yatinkarel)]

As there can be agents running even with ovn which may be consumer of these messages, i think disabling this with a config option would be safer for the user/operators who wish to disable these and knows they don't need any other agents. Will propose a patch to do so.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/neutron/+/823637

[Ihtisham ul Haq (iulhaq)]

We have similar issue but in our case `neutron.plugins.ml2.plugin.ML2Plugin.start_rpc_listeners()` is being called which fails connect to the message queue because there is none, as we are using OVN as backend and have notification driver disabled:

Neutron config:
...
  [oslo_messaging_notifications]
  driver = noop
...

Logs:
```
DEBUG neutron.plugins.ml2.plugin [req-a525ff71-2ed8-481f-a0ae-86221c918416 - - - - -] neutron.plugins.ml2.plugin.Ml2Plugin method start_rpc_listeners called with arguments () {} wrapper /usr/local/lib/python3.10/dist-packages/oslo_log/helpers.py:65
ERROR oslo.messaging._drivers.impl_rabbit [req-a525ff71-2ed8-481f-a0ae-86221c918416 - - - - -] Connection failed: [Errno 111] ECONNREFUSED (retrying in 1.0 seconds): ConnectionRefusedError: [Errno 111] ECONNREFUSED
```

So I guess the same fix about can be used to make sure to execute `start_rpc_listeners()` only if we have rpc workers.

[yatin (yatinkarel)]

@iulhaq i created a seperate bug for this https://bugs.launchpad.net/neutron/+bug/1992352, Can you check that and confirm you see similar behavior?

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/823637
Committed: https://opendev.org/openstack/neutron/commit/3e1e2d63b3383d28c9a36b00000ab89caffa3829
Submitter: "Zuul (22348)"
Branch: master

commit 3e1e2d63b3383d28c9a36b00000ab89caffa3829
Author: yatinkarel <email address hidden>
Date: Thu Jan 6 04:49:03 2022 +0000

    Enable rpc notifications only when rpc_workers >= 1

    rpc_workers can be set < 1 with 'ovn' backend when no
    other agent is running apart from ovn agents to
    consume these rpc notifications.

    Add and apply disable_notifications decorator on
    methods which do rpc cast calls to agents, the
    decorator makes the caller method execute only
    when rpc_workers >=1. This patch not changing
    default behavior and utilizes the rpc_workers config option
    to enable rpc notification on resources updates only when
    rpc_workers >= 1.

    Also set rpc_workers=0 in ovn jobs to cover this scenario.

    Closes-Bug: #1889737
    Closes-Bug: #1992352
    Change-Id: I700fe2cd422bc1eb8b5144ec116e7f0a60238419

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/neutron/+/872644
Committed: https://opendev.org/openstack/neutron/commit/47fef55e25fb1b7d3c6c7d6083a916e26fd45b6d
Submitter: "Zuul (22348)"
Branch: master

commit 47fef55e25fb1b7d3c6c7d6083a916e26fd45b6d
Author: Rodolfo Alonso Hernandez <email address hidden>
Date: Fri Feb 3 13:11:24 2023 +0100

    Add a method to retrieve and register "rpc_workers" config knob

    This new method retrieves the config option "rpc_workers" from the
    configuration. If this option is not loaded, the method registers
    the ``neutron.conf.service.SERVICE_OPTS`` options before reading
    the knob again.

    Closes-Bug: #2004656
    Related-Bug: #1889737

    Change-Id: I1f99cb32f33cc91141136cb4e3fbd33715530c59

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/neutron 22.0.0.0rc1 release candidate.