Add release note for preview of OVN

Change-Id: Ic71baf32fe3511896047069df820ccba69822d44

doc/source/1910.rst

@@ -67,6 +67,10 @@ Preview Charms
 * masakari-monitors
 * mysql-innodb-cluster
 * mysql-router
+* neutron-api-plugin-ovn
+* ovn-central
+* ovn-chassis
+* ovn-dedicated-chassis
 * pacemaker-remote
 * tempest
 
@@ -259,6 +263,72 @@ A simple example deployment:
      juju deploy -n 3 cs:~openstack-charmers-next/mysql-innodb-cluster
      juju add-relation mysql-router:db-router mysql-innodb-cluster:db-router
 
+OVN
+~~~
+
+The 19.10 OpenStack Charms release introduces a suite of four preview charms
+that allows you to model Open Virtual Network (OVN).  OVN provides open source
+network virtualization for Open vSwitch (OVS).
+
+One of the main drivers for this enablement work is the prospect of being able
+to hardware-offload everything.  This is possible due to how OVN programs
+everything in Open vSwitch with OpenFlow rules.  This in turn provides a
+uniform way of programming the hardware forwarding tables of supported NICs.
+
+Hardware-offloading is a prerequisite for effective handling of workloads with
+high bandwidth consumption.
+
+OVN also provides a more flexible way of configuring external Layer3 networking
+as OVN does not require every node (``Chassis`` in OVN terminology) in a
+deployment to have direct external connectivity.  This plays nicely with
+Layer3-only datacenter fabrics (RFC 7938).
+
+East/West traffic is distributed by default. North/South traffic is highly
+available by default.  Liveness detection is done using the Bidirectional
+Forwarding Detection (BFD) protocol.
+
+Please refer to appendix `Open Virtual Network (OVN)`_
+in the `OpenStack Charms Deployment Guide`_ for more details.
+
+Known feature gaps at this point in time:
+
+* No validation has been done with DPDK, SR-IOV or hardware-offloading in the
+  charms.
+
+* Support for the Octavia OVN provider driver has not been implemented in the
+  charms and no validation has been done with LBaaS in general.
+
+* Only limited validation has been done with other Neutron extensions, and it
+  may be possible to configure unsupported combinations of features with
+  undefined results.
+
+* There are unresolved issues with how security groups get handled in the
+  context of the ordering of resource creation through the OpenStack API / CLI.
+  If you are unable to get ingress traffic to flow to your instances after
+  initial post-deployment configuration, try to remove the default security
+  group rules and re-create them.
+
+.. code:: bash
+
+    PROJECT_ID=$(openstack project list -f value -c ID \
+                   --domain admin_domain)
+    SECGRP_ID=$(openstack security group list --project $PROJECT_ID \
+        | awk '/default/{print$2}')
+    openstack security group rule delete \
+        $(openstack security group rule list $SECGRP_ID| awk '/IPv./{print$2}')
+    openstack security group rule create --ingress --protocol any \
+        --ethertype IPv4 --remote-group $SECGRP_ID $SECGRP_ID
+    openstack security group rule create --ingress --protocol any \
+        --ethertype IPv6 --remote-group $SECGRP_ID $SECGRP_ID
+    openstack security group rule create --egress --protocol any \
+        --ethertype IPv4 $SECGRP_ID
+    openstack security group rule create --egress --protocol any \
+        --ethertype IPv6 $SECGRP_ID
+    openstack security group rule create --ingress --protocol any \
+        --ethertype IPv4 $SECGRP_ID --remote-ip YOUR_IPV4_LAB_NETWORK_CIDR
+    openstack security group rule create --ingress --protocol any \
+        --ethertype IPv6 $SECGRP_ID --remote-ip YOUR_IPV6_LAB_NETWORK_CIDR
+
 
 Upgrading charms
 ================
@@ -391,6 +461,7 @@ Please see the `OpenStack Charm Guide`_ for current information.
 
 .. LINKS
 .. _OpenStack Upgrades: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-upgrade-openstack.html
+.. _Open Virtual Network (OVN): https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest/app-ovn.html
 .. _OpenStack Charms Deployment Guide: https://docs.openstack.org/project-deploy-guide/charm-deployment-guide/latest
 .. _OpenStack Charm Guide: https://docs.openstack.org/charm-guide/latest/
 .. _19.10 milestone: https://launchpad.net/openstack-charms/+milestone/19.10