ovn: Add support for OVN SB Relay

Add support for deploying OVN SB relays [1].
This is enabled by default to improve large scale scenarios.

Default mechanism deploys one relay group per 50 ovn-controller hosts
and uses random but idempotent method to choose a relay for a given host.

neutron-server and Octavia will connect directly to SB cluster, not via
the relays.

kolla-ansible check subcommand does not support ,,iterated'' containers
for now - but will be introduced in a subsequent patch.

[1]: https://docs.ovn.org/en/latest/tutorials/ovn-ovsdb-relay.html

Co-Authored-By: Krzysztof Tomaszewski <ktomaszewski@cloudferro.com>

Depends-On: https://review.opendev.org/c/openstack/kolla/+/928898

Change-Id: Id7d6973668d8b2b194913b533f8cb756c6708536

1 files changed, 27 insertions, 0 deletions

diff --git a/doc/source/reference/networking/neutron.rst b/doc/source/reference/networking/neutron.rst
index d7cac217b..fab86ce73 100644
--- a/doc/source/reference/networking/neutron.rst
+++ b/doc/source/reference/networking/neutron.rst
@@ -231,6 +231,33 @@ To change this behaviour you need to set the following:
 
    neutron_ovn_distributed_fip: "yes"
 
+By default, the number of relay groups (``ovn_sb_db_relay_count``) is computed
+by dividing the total number of ``ovn-controller`` hosts by the value in
+``ovn_sb_db_relay_compute_per_relay`` (which defaults to 50), and rounding up.
+For instance, if you have 120 hosts in the ``ovn-controller`` group, you would
+get ``ceil(120 / 50) = 3`` relay groups.
+You can override ``ovn_sb_db_relay_compute_per_relay`` to scale how many hosts
+each relay group handles, for example:
+
+.. code-block:: yaml
+
+   ovn_sb_db_relay_compute_per_relay: 25
+
+You can also bypass the automatic calculation and manually set a fixed number
+of relay groups with ``ovn_sb_db_relay_count``:
+
+.. code-block:: yaml
+
+   ovn_sb_db_relay_count: 10
+
+.. note::
+   If you set ``ovn_sb_db_relay_count`` explicitly, it effectively overrides
+   the calculated count based on ``ovn_sb_db_relay_compute_per_relay``.
+
+It is also possible to set a static mapping between a ``ovn-controller`` host
+(network node or hypervisor) and particular OVN relay using an Ansible host_var
+``ovn_sb_db_relay_client_group_id``.
+
 Similarly - in order to have Neutron DHCP agents deployed in OVN networking
 scenario, use: