diff --git a/requirements.txt b/requirements.txt
index 20f335d..f65abf7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -4,4 +4,6 @@
 #
 # Build requirements
 charm-tools>=2.4.4
+# importlib-resources 1.1.0 removed Python 3.5 support
+importlib-resources<1.1.0
 simplejson
diff --git a/src/lib/charm/openstack/ovn_central.py b/src/lib/charm/openstack/ovn_central.py
index 59433f5..f9e8950 100644
--- a/src/lib/charm/openstack/ovn_central.py
+++ b/src/lib/charm/openstack/ovn_central.py
@@ -26,51 +26,38 @@ import charms.ovn as ovn
 import charms.ovn_charm as ovn_charm
 
 
-class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
-    # OpenvSwitch and OVN is distributed as part of the Ubuntu Cloud Archive
-    # Pockets get their name from OpenStack releases
-    release = 'train'
+class BaseOVNCentralCharm(charms_openstack.charm.OpenStackCharm):
+    abstract_class = True
     package_codenames = {
         'ovn-central': collections.OrderedDict([
-            ('2.12', 'train'),
+            ('2', 'train'),
+            ('20', 'ussuri'),
         ]),
     }
     name = 'ovn-central'
     packages = ['ovn-central']
     services = ['ovn-central']
+    release_pkg = 'ovn-central'
     required_relations = ['certificates']
-    # NOTE(fnordahl) we replace the package sysv init script with our own
-    # systemd service files.
-    #
-    # The issue that triggered this change is that to be able to pass the
-    # correct command line arguments to ``ovn-nortrhd`` we need to create
-    # a ``/etc/openvswitch/ovn-northd-db-params.conf`` which has the side
-    # effect of profoundly changing the behaviour of the ``ovn-ctl`` tool
-    # that the ``ovn-central`` init script makes use of.
-    #
-    # https://github.com/ovn-org/ovn/blob/dc0e10c068c20c4e59c9c86ecee26baf8ed50e90/utilities/ovn-ctl#L323
-    #
-    # TODO: The systemd service files should be upstreamed and removed from
-    # the charm
     restart_map = {
         '/etc/default/ovn-central': services,
         os.path.join(
-            ovn_charm.OVS_ETCDIR, 'ovn-northd-db-params.conf'): ['ovn-northd'],
-        '/lib/systemd/system/ovn-central.service': [],
-        '/lib/systemd/system/ovn-northd.service': [],
-        '/lib/systemd/system/ovn-nb-ovsdb.service': [],
-        '/lib/systemd/system/ovn-sb-ovsdb.service': [],
+            ovn.ovn_sysconfdir(), 'ovn-northd-db-params.conf'): ['ovn-northd'],
     }
     python_version = 3
     source_config_key = 'source'
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)
-        charms_openstack.adapters.config_property(ovn_charm.ovn_key)
-        charms_openstack.adapters.config_property(ovn_charm.ovn_cert)
-        charms_openstack.adapters.config_property(ovn_charm.ovn_ca_cert)
+        try:
+            charms_openstack.adapters.config_property(ovn_charm.ovn_key)
+            charms_openstack.adapters.config_property(ovn_charm.ovn_cert)
+            charms_openstack.adapters.config_property(ovn_charm.ovn_ca_cert)
+        except RuntimeError:
+            # The custom config properties are allready registered
+            pass
 
-    def install(self):
+    def install(self, service_masks=None):
         """Extend the default install method.
 
         Mask services before initial installation.
@@ -84,15 +71,9 @@ class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
         We also configure source before installing as OpenvSwitch and OVN
         packages are distributed as part of the UCA.
         """
-        # NOTE(fnordahl) The OVN central components are currently packaged with
-        # a dependency on openvswitch-switch, but it does not need the switch
-        # or stock ovsdb running.
-        service_masks = [
-            'openvswitch-switch.service',
-            'ovs-vswitchd.service',
-            'ovsdb-server.service',
-            'ovn-central.service',
-        ]
+        # NOTE(fnordahl): The actual masks are provided by the release specific
+        # classes.
+        service_masks = service_masks or []
         for service_file in service_masks:
             abs_path_svc = os.path.join('/etc/systemd/system', service_file)
             if not os.path.islink(abs_path_svc):
@@ -169,6 +150,20 @@ class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
     def join_cluster(self, db_file, schema_name, local_conn, remote_conn):
         """Maybe create a OVSDB file with remote peer connection information.
 
+        This function will return immediately if the database file already
+        exists.
+
+        Because of a shortcoming in the ``ovn-ctl`` script used to start the
+        OVN databases we call to ``ovsdb-tool join-cluster`` ourself.
+
+        That will create a database file on disk with the required information
+        and the ``ovn-ctl`` script will not touch it.
+
+        The ``ovn-ctl`` ``db-nb-cluster-remote-addr`` and
+        ``db-sb-cluster-remote-addr`` configuration options only take one
+        remote and one must be provided for correct startup, but the values in
+        the on-disk database file will be used by the ``ovsdb-server`` process.
+
         :param db_file: Full path to OVSDB file
         :type db_file: str
         :param schema_name: OVSDB Schema [OVN_Northbound, OVN_Southbound]
@@ -179,9 +174,16 @@ class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
         :type remote_conn: Union[str, ...]
         :raises: subprocess.CalledProcessError
         """
-        if os.path.exists(db_file):
+        if self.release == 'train':
+            absolute_path = os.path.join('/var/lib/openvswitch', db_file)
+        else:
+            absolute_path = os.path.join('/var/lib/ovn', db_file)
+        if os.path.exists(absolute_path):
+            ch_core.hookenv.log('OVN database "{}" exists on disk, not '
+                                'creating a new one joining cluster',
+                                level=ch_core.hookenv.DEBUG)
             return
-        cmd = ['ovsdb-tool', 'join-cluster', db_file, schema_name]
+        cmd = ['ovsdb-tool', 'join-cluster', absolute_path, schema_name]
         cmd.extend(list(local_conn))
         cmd.extend(list(remote_conn))
         ch_core.hookenv.log(cmd, level=ch_core.hookenv.INFO)
@@ -206,7 +208,7 @@ class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
                 else:
                     crt.write(tls_object['ca'])
 
-            self.configure_cert(ovn_charm.OVS_ETCDIR,
+            self.configure_cert(ovn.ovn_sysconfdir(),
                                 tls_object['cert'],
                                 tls_object['key'],
                                 cn='host')
@@ -349,3 +351,83 @@ class OVNCentralCharm(charms_openstack.charm.OpenStackCharm):
                     delete_rules.append(num)
         for rule in sorted(delete_rules, reverse=True):
             ch_ufw.modify_access(None, dst=None, action='delete', index=rule)
+
+
+class TrainOVNCentralCharm(BaseOVNCentralCharm):
+    # OpenvSwitch and OVN is distributed as part of the Ubuntu Cloud Archive
+    # Pockets get their name from OpenStack releases
+    release = 'train'
+
+    # NOTE(fnordahl) we have to replace the package sysv init script with
+    # systemd service files, this should be removed from the charm when the
+    # systemd service files committed to Focal can be backported to the Train
+    # UCA.
+    #
+    # The issue that triggered this change is that to be able to pass the
+    # correct command line arguments to ``ovn-nortrhd`` we need to create
+    # a ``/etc/openvswitch/ovn-northd-db-params.conf`` which has the side
+    # effect of profoundly changing the behaviour of the ``ovn-ctl`` tool
+    # that the ``ovn-central`` init script makes use of.
+    #
+    # https://github.com/ovn-org/ovn/blob/dc0e10c068c20c4e59c9c86ecee26baf8ed50e90/utilities/ovn-ctl#L323
+    def __init__(self, **kwargs):
+        """Override class init to adjust restart_map for Train.
+
+        NOTE(fnordahl): the restart_map functionality in charms.openstack
+        combines the process of writing a charm template to disk and
+        restarting a service whenever the target file changes.
+
+        In this instance we are only interested in getting the files written
+        to disk.  The restart operation will be taken care of when
+        ``/etc/default/ovn-central`` as defined in ``BaseOVNCentralCharm``.
+        """
+        super().__init__(**kwargs)
+        self.restart_map.update({
+            '/lib/systemd/system/ovn-central.service': [],
+            '/lib/systemd/system/ovn-northd.service': [],
+            '/lib/systemd/system/ovn-nb-ovsdb.service': [],
+            '/lib/systemd/system/ovn-sb-ovsdb.service': [],
+        })
+
+    def install(self):
+        """Override charm install method.
+
+        NOTE(fnordahl) At Train, the OVN central components is packaged with
+        a dependency on openvswitch-switch, but it does not need the switch
+        or stock ovsdb running.
+        """
+        service_masks = [
+            'openvswitch-switch.service',
+            'ovs-vswitchd.service',
+            'ovsdb-server.service',
+            'ovn-central.service',
+        ]
+        super().install(service_masks=service_masks)
+
+
+class UssuriOVNCentralCharm(BaseOVNCentralCharm):
+    # OpenvSwitch and OVN is distributed as part of the Ubuntu Cloud Archive
+    # Pockets get their name from OpenStack releases
+    release = 'ussuri'
+
+    def __init__(self, **kwargs):
+        """Override class init to adjust service map for Ussuri."""
+        super().__init__(**kwargs)
+        # We need to list the OVN ovsdb-server services explicitly so they get
+        # unmasked on render of ``ovn-central``.
+        self.services.extend([
+            'ovn-ovsdb-server-nb',
+            'ovn-ovsdb-server-sb',
+        ])
+
+    def install(self):
+        """Override charm install method."""
+
+        # This is done to prevent extraneous standalone DB initialization and
+        # subsequent upgrade to clustered DB when configuration is rendered.
+        service_masks = [
+            'ovn-central.service',
+            'ovn-ovsdb-server-nb.service',
+            'ovn-ovsdb-server-sb.service',
+        ]
+        super().install(service_masks=service_masks)
diff --git a/src/metadata.yaml b/src/metadata.yaml
index 95e2425..ef833f7 100644
--- a/src/metadata.yaml
+++ b/src/metadata.yaml
@@ -26,6 +26,7 @@ tags:
 series:
   - bionic
   - eoan
+  - focal
 subordinate: false
 provides:
   ovsdb:
diff --git a/src/reactive/ovn_central_handlers.py b/src/reactive/ovn_central_handlers.py
index b00ec8e..bafa39a 100644
--- a/src/reactive/ovn_central_handlers.py
+++ b/src/reactive/ovn_central_handlers.py
@@ -27,6 +27,7 @@ charms_openstack.bus.discover()
 charm.use_defaults(
     'charm.installed',
     'config.changed',
+    'charm.default-select-release',
     'update-status',
     'upgrade-charm',
 )
@@ -121,7 +122,9 @@ def configure_firewall():
                 ovsdb_peer.db_sb_cluster_port,
                 ovsdb_peer.db_nb_cluster_port,):
             ovsdb_peer.cluster_remote_addrs,
-            (ovsdb_peer.db_nb_port,):
+            # NOTE(fnordahl): Tactical workaround for LP: #1864640
+            (ovsdb_peer.db_nb_port,
+                ovsdb_peer.db_sb_admin_port,):
             ovsdb_cms.client_remote_addrs if ovsdb_cms else None,
         })
         ovn_charm.assess_status()
@@ -142,6 +145,17 @@ def publish_addr_to_clients():
         ep.publish_cluster_local_addr(ovsdb_peer.cluster_local_addr)
 
 
+@reactive.when_none('run-default-update-status')
+@reactive.when('config.changed.source', 'ovsdb-peer.available')
+def maybe_do_upgrade():
+    ovsdb_peer = reactive.endpoint_from_flag('ovsdb-peer.available')
+    with charm.provide_charm_instance() as ovn_charm:
+        ovn_charm.configure_source()
+        ovn_charm.upgrade_if_available([ovsdb_peer])
+        reactive.clear_flag('config.changed.source')
+        ovn_charm.assess_status()
+
+
 @reactive.when_none('run-default-update-status')
 @reactive.when('ovsdb-peer.available',
                'leadership.set.nb_cid',
@@ -164,16 +178,14 @@ def render():
         #
         # Replace this with functionality in ``ovn-ctl`` when support has been
         # added upstream.
-        ovn_charm.join_cluster('/var/lib/openvswitch/ovnnb_db.db',
-                               'OVN_Northbound',
+        ovn_charm.join_cluster('ovnnb_db.db', 'OVN_Northbound',
                                ovsdb_peer.db_connection_strs(
                                    (ovsdb_peer.cluster_local_addr,),
                                    ovsdb_peer.db_nb_cluster_port),
                                ovsdb_peer.db_connection_strs(
                                    ovsdb_peer.cluster_remote_addrs,
                                    ovsdb_peer.db_nb_cluster_port))
-        ovn_charm.join_cluster('/var/lib/openvswitch/ovnsb_db.db',
-                               'OVN_Southbound',
+        ovn_charm.join_cluster('ovnsb_db.db', 'OVN_Southbound',
                                ovsdb_peer.db_connection_strs(
                                    (ovsdb_peer.cluster_local_addr,),
                                    ovsdb_peer.db_sb_cluster_port),
diff --git a/src/templates/ovn-central b/src/templates/train/ovn-central
similarity index 67%
rename from src/templates/ovn-central
rename to src/templates/train/ovn-central
index 1a5bd21..43a071a 100644
--- a/src/templates/ovn-central
+++ b/src/templates/train/ovn-central
@@ -6,11 +6,19 @@
 # Configuration managed by ovn-central charm
 ###############################################################################
 
-# FORCE_COREFILES: If 'yes' then core files will be enabled.
-# FORCE_COREFILES=yes
-
 # OVN_CTL_OPTS: Extra options to pass to ovs-ctl.  This is, for example,
 # a suitable place to specify --ovn-northd-wrapper=valgrind.
+
+# NOTE(fnordahl): Cluster join is directed towards all peers by a direct call
+# to `ovsdb-tool join-cluster` by the charm.
+#
+# That will create a database file on disk with the required information and
+# the `ovn-ctl` script will not touch it.
+#
+# The `ovn-ctl` `db-nb-cluster-remote-addr` and `db-sb-cluster-remote-addr`
+# configuration options only take one remote and one must be provided for
+# correct startup, but the values in the on-disk database file will be used by
+# `ovsdb-server`.
 OVN_CTL_OPTS=--db-nb-file=/var/lib/openvswitch/ovnnb_db.db \
     --db-nb-cluster-local-addr={{ ovsdb_peer.cluster_local_addr }} \
     --db-nb-cluster-local-port={{ ovsdb_peer.db_nb_cluster_port }} \
@@ -29,17 +37,5 @@ OVN_CTL_OPTS=--db-nb-file=/var/lib/openvswitch/ovnnb_db.db \
     --ovn-sb-db-ssl-cert={{ options.ovn_cert }} \
     --ovn-sb-db-ssl-ca-cert={{ options.ovn_ca_cert }} \
     --db-sb-cluster-remote-addr={{ ovsdb_peer.cluster_remote_addrs | first }} \
-    --db-nb-cluster-remote-port={{ ovsdb_peer.db_nb_cluster_port }} \
+    --db-sb-cluster-remote-port={{ ovsdb_peer.db_sb_cluster_port }} \
     --db-sb-cluster-remote-proto=ssl
-
-# DPDK options are now configured via ovs-vsctl/ovsdb, see:
-# - /usr/share/doc/openvswitch-common/INSTALL.DPDK.md.gz
-# - /usr/share/doc/openvswitch-common/INSTALL.DPDK-ADVANCED.md.gz
-# dpdk-extra is the fallback for users who formerly set e.g.
-#  '--vhost-owner libvirt-qemu:kvm --vhost-perm 0664'
-# here or any other DPDK EAL arguments via DPDK_OPTS which are not covered by
-# the default switches provided by ovs-vsctl.
-# This is an arbitrary string that will get appended to the EAL commandline.
-# For more on the new ovsdb based configuration of DPDK features, see:
-# `man ovs-vswitchd.conf.db`
-
diff --git a/src/templates/ovn-central.service b/src/templates/train/ovn-central.service
similarity index 100%
rename from src/templates/ovn-central.service
rename to src/templates/train/ovn-central.service
diff --git a/src/templates/ovn-nb-ovsdb.service b/src/templates/train/ovn-nb-ovsdb.service
similarity index 100%
rename from src/templates/ovn-nb-ovsdb.service
rename to src/templates/train/ovn-nb-ovsdb.service
diff --git a/src/templates/ovn-northd.service b/src/templates/train/ovn-northd.service
similarity index 100%
rename from src/templates/ovn-northd.service
rename to src/templates/train/ovn-northd.service
diff --git a/src/templates/ovn-sb-ovsdb.service b/src/templates/train/ovn-sb-ovsdb.service
similarity index 100%
rename from src/templates/ovn-sb-ovsdb.service
rename to src/templates/train/ovn-sb-ovsdb.service
diff --git a/src/templates/ussuri/ovn-central b/src/templates/ussuri/ovn-central
new file mode 100644
index 0000000..dc9d2db
--- /dev/null
+++ b/src/templates/ussuri/ovn-central
@@ -0,0 +1,40 @@
+# This is a systemd EnvironmentFile as documented in systemd.exec(5)
+#
+###############################################################################
+# [ WARNING ]
+# Configuration file maintained by Juju. Local changes may be overwritten.
+# Configuration managed by ovn-central charm
+###############################################################################
+
+# OVN_CTL_OPTS: Extra options to pass to ovs-ctl.  This is, for example,
+# a suitable place to specify --ovn-northd-wrapper=valgrind.
+
+# NOTE(fnordahl): Cluster join is directed towards all peers by a direct call
+# to `ovsdb-tool join-cluster` by the charm.
+#
+# That will create a database file on disk with the required information and
+# the `ovn-ctl` script will not touch it.
+#
+# The `ovn-ctl` `db-nb-cluster-remote-addr` and `db-sb-cluster-remote-addr`
+# configuration options only take one remote and one must be provided for
+# correct startup, but the values in the on-disk database file will be used by
+# `ovsdb-server`.
+OVN_CTL_OPTS= \
+    --db-nb-cluster-local-addr={{ ovsdb_peer.cluster_local_addr }} \
+    --db-nb-cluster-local-port={{ ovsdb_peer.db_nb_cluster_port }} \
+    --db-nb-cluster-local-proto=ssl \
+    --ovn-nb-db-ssl-key={{ options.ovn_key }} \
+    --ovn-nb-db-ssl-cert={{ options.ovn_cert }} \
+    --ovn-nb-db-ssl-ca-cert={{ options.ovn_ca_cert }} \
+    --db-nb-cluster-remote-addr={{ ovsdb_peer.cluster_remote_addrs | first }} \
+    --db-nb-cluster-remote-port={{ ovsdb_peer.db_nb_cluster_port }} \
+    --db-nb-cluster-remote-proto=ssl \
+    --db-sb-cluster-local-addr={{ ovsdb_peer.cluster_local_addr }} \
+    --db-sb-cluster-local-port={{ ovsdb_peer.db_sb_cluster_port }} \
+    --db-sb-cluster-local-proto=ssl \
+    --ovn-sb-db-ssl-key={{ options.ovn_key }} \
+    --ovn-sb-db-ssl-cert={{ options.ovn_cert }} \
+    --ovn-sb-db-ssl-ca-cert={{ options.ovn_ca_cert }} \
+    --db-sb-cluster-remote-addr={{ ovsdb_peer.cluster_remote_addrs | first }} \
+    --db-sb-cluster-remote-port={{ ovsdb_peer.db_sb_cluster_port }} \
+    --db-sb-cluster-remote-proto=ssl
diff --git a/src/tests/bundles/bionic.yaml b/src/tests/bundles/bionic-train.yaml
similarity index 100%
rename from src/tests/bundles/bionic.yaml
rename to src/tests/bundles/bionic-train.yaml
diff --git a/src/tests/bundles/bionic-ussuri.yaml b/src/tests/bundles/bionic-ussuri.yaml
new file mode 100644
index 0000000..6ca8df0
--- /dev/null
+++ b/src/tests/bundles/bionic-ussuri.yaml
@@ -0,0 +1,19 @@
+series: bionic
+relations:
+- - vault:shared-db
+  - mysql:shared-db
+- - ovn-central:certificates
+  - vault:certificates
+applications:
+  mysql:
+    charm: cs:~openstack-charmers-next/percona-cluster
+    num_units: 1
+  vault:
+    charm: cs:~openstack-charmers-next/vault
+    num_units: 1
+  ovn-central:
+    series: bionic
+    charm: cs:~openstack-charmers-next/ovn-central
+    num_units: 3
+    options:
+      source: cloud:bionic-ussuri/proposed
diff --git a/src/tests/bundles/eoan.yaml b/src/tests/bundles/eoan.yaml
index 0418aa4..3846007 100644
--- a/src/tests/bundles/eoan.yaml
+++ b/src/tests/bundles/eoan.yaml
@@ -1,13 +1,17 @@
 series: eoan
 relations:
+- - vault-mysql-router:db-router
+  - mysql-innodb-cluster:db-router
 - - vault:shared-db
-  - mysql:shared-db
+  - vault-mysql-router:shared-db
 - - ovn-central:certificates
   - vault:certificates
 applications:
-  mysql:
+  mysql-innodb-cluster:
     charm: cs:~openstack-charmers-next/mysql-innodb-cluster
     num_units: 3
+  vault-mysql-router:
+    charm: cs:~openstack-charmers-next/mysql-router
   vault:
     charm: cs:~openstack-charmers-next/vault
     num_units: 1
diff --git a/src/tests/bundles/focal.yaml b/src/tests/bundles/focal.yaml
new file mode 100644
index 0000000..673b0d2
--- /dev/null
+++ b/src/tests/bundles/focal.yaml
@@ -0,0 +1,21 @@
+series: focal
+relations:
+- - vault-mysql-router:db-router
+  - mysql-innodb-cluster:db-router
+- - vault:shared-db
+  - vault-mysql-router:shared-db
+- - ovn-central:certificates
+  - vault:certificates
+applications:
+  mysql-innodb-cluster:
+    charm: cs:~openstack-charmers-next/mysql-innodb-cluster
+    num_units: 3
+  vault-mysql-router:
+    charm: cs:~openstack-charmers-next/mysql-router
+  vault:
+    charm: cs:~openstack-charmers-next/vault
+    num_units: 1
+  ovn-central:
+    series: focal
+    charm: cs:~openstack-charmers-next/ovn-central
+    num_units: 3
diff --git a/src/tests/tests.yaml b/src/tests/tests.yaml
index 2942112..6ffc598 100644
--- a/src/tests/tests.yaml
+++ b/src/tests/tests.yaml
@@ -1,9 +1,12 @@
 charm_name: ovn-central
 gate_bundles:
+- bionic-train
 - eoan
-- bionic
+- bionic-ussuri
 smoke_bundles:
-- bionic
+- bionic-ussuri
+dev_bundles:
+- focal
 target_deploy_status:
   ovn-central:
     workload-status: blocked
diff --git a/test-requirements.txt b/test-requirements.txt
index 14b380e..c43a8db 100644
--- a/test-requirements.txt
+++ b/test-requirements.txt
@@ -3,11 +3,10 @@
 # requirements management in charms via bot-control.  Thank you.
 #
 # Lint and unit test requirements
-flake8>=2.2.4,<=2.4.1
-stestr>=2.2.0
-requests>=2.18.4
-charms.reactive
-mock>=1.2
-nose>=1.3.7
 coverage>=3.6
+mock>=1.2
+pep8>=1.7.0
+flake8>=2.2.4
+os-testr>=0.4.1
+
 git+https://github.com/openstack/charms.openstack.git#egg=charms.openstack
diff --git a/tox.ini b/tox.ini
index 23750a8..1d1b04a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -77,4 +77,5 @@ commands = {posargs}
 
 [flake8]
 # E402 ignore necessary for path append before sys module import in actions
-ignore = E402
+# W504 is necessary as both W503 and W504 is enabled in flake8 at the same time
+ignore = E402,W504
diff --git a/unit_tests/__init__.py b/unit_tests/__init__.py
index dffc71c..661d3fc 100644
--- a/unit_tests/__init__.py
+++ b/unit_tests/__init__.py
@@ -22,22 +22,55 @@ import charms_openstack.test_mocks  # noqa
 charms_openstack.test_mocks.mock_charmhelpers()
 
 import mock
-import charms
+
+
+class _fake_decorator(object):
+
+    def __init__(self, *args):
+        pass
+
+    def __call__(self, f):
+        return f
+
+
+charms = mock.MagicMock()
+sys.modules['charms'] = charms
 charms.leadership = mock.MagicMock()
+sys.modules['charms.leadership'] = charms.leadership
+charms.reactive = mock.MagicMock()
+charms.reactive.when = _fake_decorator
+charms.reactive.when_all = _fake_decorator
+charms.reactive.when_any = _fake_decorator
+charms.reactive.when_not = _fake_decorator
+charms.reactive.when_none = _fake_decorator
+charms.reactive.when_not_all = _fake_decorator
+charms.reactive.not_unless = _fake_decorator
+charms.reactive.when_file_changed = _fake_decorator
+charms.reactive.collect_metrics = _fake_decorator
+charms.reactive.meter_status_changed = _fake_decorator
+charms.reactive.only_once = _fake_decorator
+charms.reactive.hook = _fake_decorator
+charms.reactive.bus = mock.MagicMock()
+charms.reactive.flags = mock.MagicMock()
+charms.reactive.relations = mock.MagicMock()
+sys.modules['charms.reactive'] = charms.reactive
+sys.modules['charms.reactive.bus'] = charms.reactive.bus
+sys.modules['charms.reactive.bus'] = charms.reactive.decorators
+sys.modules['charms.reactive.flags'] = charms.reactive.flags
+sys.modules['charms.reactive.relations'] = charms.reactive.relations
 charms.ovn = mock.MagicMock()
-charms.ovn_charm = mock.MagicMock()
-keystoneauth1 = mock.MagicMock()
-neutronclient = mock.MagicMock()
-sys.modules['charms.leadership'] = charms.leadership
 sys.modules['charms.ovn'] = charms.ovn
-sys.modules['charms.ovn_charm'] = charms.ovn_charm
+charms.ovn_charm = mock.MagicMock()
+sys.modules['charms.ovn_charm'] = charms.ovn
 keystoneauth1 = mock.MagicMock()
-novaclient = mock.MagicMock()
-neutron_lib = mock.MagicMock()
-sys.modules['charms.leadership'] = charms.leadership
 sys.modules['keystoneauth1'] = keystoneauth1
-sys.modules['novaclient'] = novaclient
+netaddr = mock.MagicMock()
+sys.modules['netaddr'] = netaddr
+neutronclient = mock.MagicMock()
 sys.modules['neutronclient'] = neutronclient
 sys.modules['neutronclient.v2_0'] = neutronclient.v2_0
+neutron_lib = mock.MagicMock()
 sys.modules['neutron_lib'] = neutron_lib
 sys.modules['neutron_lib.constants'] = neutron_lib.constants
+novaclient = mock.MagicMock()
+sys.modules['novaclient'] = novaclient
diff --git a/unit_tests/test_lib_charms_ovn_central.py b/unit_tests/test_lib_charms_ovn_central.py
index ec5e042..5901442 100644
--- a/unit_tests/test_lib_charms_ovn_central.py
+++ b/unit_tests/test_lib_charms_ovn_central.py
@@ -14,7 +14,6 @@
 
 import io
 import mock
-import os
 
 import charms_openstack.test_utils as test_utils
 
@@ -25,10 +24,10 @@ class Helper(test_utils.PatchHelper):
 
     def setUp(self):
         super().setUp()
-        self.patch_release(ovn_central.OVNCentralCharm.release)
+        self.patch_release(ovn_central.UssuriOVNCentralCharm.release)
         self.patch_object(
             ovn_central.charms_openstack.adapters, 'config_property')
-        self.target = ovn_central.OVNCentralCharm()
+        self.target = ovn_central.UssuriOVNCentralCharm()
 
     def patch_target(self, attr, return_value=None):
         mocked = mock.patch.object(self.target, attr)
@@ -41,13 +40,16 @@ class Helper(test_utils.PatchHelper):
 
 class TestOVNCentralCharm(Helper):
 
-    def test_install(self):
+    def test_install_train(self):
+        self.patch_release(ovn_central.TrainOVNCentralCharm.release)
+        self.target = ovn_central.TrainOVNCentralCharm()
         self.patch_object(ovn_central.charms_openstack.charm.OpenStackCharm,
                           'install')
         self.patch_object(ovn_central.os.path, 'islink')
         self.islink.return_value = False
         self.patch_object(ovn_central.os, 'symlink')
         self.patch_target('configure_source')
+        self.patch_object(ovn_central.os, 'mkdir')
         self.target.install()
         calls = []
         for service in ('openvswitch-switch', 'ovs-vswitchd', 'ovsdb-server',
@@ -65,6 +67,32 @@ class TestOVNCentralCharm(Helper):
         self.install.assert_called_once_with()
         self.configure_source.assert_called_once_with()
 
+    def test_install(self):
+        self.patch_object(ovn_central.charms_openstack.charm.OpenStackCharm,
+                          'install')
+        self.patch_object(ovn_central.os.path, 'islink')
+        self.islink.return_value = False
+        self.patch_object(ovn_central.os, 'symlink')
+        self.patch_target('configure_source')
+        self.patch_object(ovn_central.os, 'mkdir')
+        self.target.install()
+        calls = []
+        for service in (self.target.services[0],
+                        'ovn-ovsdb-server-nb',
+                        'ovn-ovsdb-server-sb',):
+            calls.append(
+                mock.call('/etc/systemd/system/{}.service'.format(service)))
+        self.islink.assert_has_calls(calls)
+        calls = []
+        for service in (self.target.services[0], 'ovn-ovsdb-server-nb',
+                        'ovn-ovsdb-server-sb',):
+            calls.append(
+                mock.call('/dev/null',
+                          '/etc/systemd/system/{}.service'.format(service)))
+        self.symlink.assert_has_calls(calls)
+        self.install.assert_called_once_with()
+        self.configure_source.assert_called_once_with()
+
     def test__default_port_list(self):
         self.assertEquals(
             self.target._default_port_list(),
@@ -155,20 +183,20 @@ class TestOVNCentralCharm(Helper):
             'chain': 'fakechain',
         }]
         self.patch_object(ovn_central, 'ovn_charm')
-        self.ovn_charm.OVS_ETCDIR = '/etc/openvswitch'
-        self.ovn_charm.ovn_ca_cert.return_value = os.path.join(
-            self.ovn_charm.OVS_ETCDIR, 'ovn-central.crt')
+        self.ovn_charm.ovn_ca_cert.return_value = '/etc/ovn/ovn-central.crt'
+        self.patch_object(ovn_central.ovn, 'ovn_sysconfdir')
+        self.ovn_sysconfdir.return_value = '/etc/ovn'
         with mock.patch('builtins.open', create=True) as mocked_open:
             mocked_file = mock.MagicMock(spec=io.FileIO)
             mocked_open.return_value = mocked_file
             self.target.configure_cert = mock.MagicMock()
             self.target.configure_tls()
             mocked_open.assert_called_once_with(
-                '/etc/openvswitch/ovn-central.crt', 'w')
+                '/etc/ovn/ovn-central.crt', 'w')
             mocked_file.__enter__().write.assert_called_once_with(
                 'fakeca\nfakechain')
             self.target.configure_cert.assert_called_once_with(
-                self.ovn_charm.OVS_ETCDIR,
+                '/etc/ovn',
                 'fakecert',
                 'fakekey',
                 cn='host')
diff --git a/unit_tests/test_reactive_ovn_central_handlers.py b/unit_tests/test_reactive_ovn_central_handlers.py
index 0514e21..e4a920b 100644
--- a/unit_tests/test_reactive_ovn_central_handlers.py
+++ b/unit_tests/test_reactive_ovn_central_handlers.py
@@ -25,6 +25,7 @@ class TestRegisteredHooks(test_utils.TestRegisteredHooks):
         defaults = [
             'charm.installed',
             'config.changed',
+            'charm.default-select-release',
             'update-status',
             'upgrade-charm',
         ]
@@ -39,6 +40,7 @@ class TestRegisteredHooks(test_utils.TestRegisteredHooks):
                 'initialize_ovsdbs': ('run-default-update-status',
                                       'leadership.set.nb_cid',
                                       'leadership.set.sb_cid',),
+                'maybe_do_upgrade': ('run-default-update-status',),
                 'publish_addr_to_clients': ('run-default-update-status',),
                 'render': ('run-default-update-status',),
             },
@@ -55,6 +57,8 @@ class TestRegisteredHooks(test_utils.TestRegisteredHooks):
                 'initialize_ovsdbs': ('charm.installed',
                                       'leadership.is_leader',
                                       'ovsdb-peer.connected',),
+                'maybe_do_upgrade': ('config.changed.source',
+                                     'ovsdb-peer.available',),
                 'publish_addr_to_clients': ('ovsdb-peer.available',
                                             'leadership.set.nb_cid',
                                             'leadership.set.sb_cid',
@@ -76,7 +80,6 @@ class TestOvnCentralHandlers(test_utils.PatchHelper):
 
     def setUp(self):
         super().setUp()
-        # self.patch_release(octavia.OctaviaCharm.release)
         self.target = mock.MagicMock()
         self.patch_object(handlers.charm, 'provide_charm_instance',
                           new=mock.MagicMock())
@@ -149,7 +152,8 @@ class TestOvnCentralHandlers(test_utils.PatchHelper):
                 ovsdb_peer.db_sb_cluster_port,
                 ovsdb_peer.db_nb_cluster_port,):
             ovsdb_peer.cluster_remote_addrs,
-            (ovsdb_peer.db_nb_port,): None,
+            (ovsdb_peer.db_nb_port,
+                ovsdb_peer.db_sb_admin_port,): None,
         })
         self.target.assess_status.assert_called_once_with()
         self.target.configure_firewall.reset_mock()
@@ -162,8 +166,8 @@ class TestOvnCentralHandlers(test_utils.PatchHelper):
                 ovsdb_peer.db_sb_cluster_port,
                 ovsdb_peer.db_nb_cluster_port,):
             ovsdb_peer.cluster_remote_addrs,
-            (ovsdb_peer.db_nb_port,):
-            ovsdb_cms.client_remote_addrs,
+            (ovsdb_peer.db_nb_port,
+                ovsdb_peer.db_sb_admin_port,): ovsdb_cms.client_remote_addrs,
         })
 
     def test_publish_addr_to_clients(self):
@@ -196,11 +200,11 @@ class TestOvnCentralHandlers(test_utils.PatchHelper):
         self.target.render_with_interfaces.assert_called_once_with(
             [ovsdb_peer])
         self.target.join_cluster.assert_has_calls([
-            mock.call('/var/lib/openvswitch/ovnnb_db.db',
+            mock.call('ovnnb_db.db',
                       'OVN_Northbound',
                       connection_strs,
                       connection_strs),
-            mock.call('/var/lib/openvswitch/ovnsb_db.db',
+            mock.call('ovnsb_db.db',
                       'OVN_Southbound',
                       connection_strs,
                       connection_strs),