Implement experimental features framework

During the Zed PTG it was decided to handle unsupported features in
Neutron as experimental. See section titled "When we say something is
not supported?", day 2 in [1]. The agreement was:

"We keep existing jobs for linuxbridge driver for example, but when the
tests start to fail we skip them and finally we stop the job also.
To make it clear for operators we add warning logs highlighting that the
given feature/driver is experimental, and introduce cfg option to enable
such features explicitly."

This commit implements this agreement, initially with Linuxbridge

Depends-On: https://review.opendev.org/c/openstack/neutron-tempest-plugin/+/845646

[1] https://lists.openstack.org/pipermail/openstack-discuss/2022-April/028164.html

Change-Id: Ib18efa3f472736b58c8967847b1061da0e3897d7

doc/source/admin/config-experimental-framework.rst

@@ -0,0 +1,37 @@
+.. _config-experimental-framework:
+
+===============================
+Experimental features framework
+===============================
+
+Some Neutron features are not supported because the community doesn't have
+the resources and/or technical expertise to maintain them anymore. As they
+arise, the Neutron team designates these features as experimental. Deployers
+can continue using these features at their own risk, by explicitly enabling
+them in the ``experimental`` section of ``neutron.conf``.
+
+.. note::
+   Of course, the Neutron core team would love to return experimetal features
+   to the supported status, if interested parties step up to maintain them. If
+   you are interested in maintaining any of the experimental features listed
+   below, please contact the PTL shown in the
+   `Neutron project page
+   <https://governance.openstack.org/tc/reference/projects/neutron.html>`_.
+
+The following table shows the Neutron features currently designated as
+experimetal:
+
+.. table:: **Neutron Experimental features**
+
+    =========================  ===================================
+     Feature                    Option in neutron.conf to enable
+    =========================  ===================================
+     ML2 Linuxbridge driver     linuxbridge
+    =========================  ===================================
+
+This is an example of how to enable the use of an experimental feature:
+
+.. code-block:: none
+
+   [experimental]
+   linuxbridge = true

doc/source/admin/config.rst

@@ -18,6 +18,7 @@ Configuration
    config-dns-int-ext-serv
    config-dns-res
    config-dvr-ha-snat
+   config-experimental-framework
    config-fip-port-forwardings
    config-ipam
    config-ipv6

etc/oslo-config-generator/neutron.conf

@@ -5,6 +5,7 @@ wrap_width = 79
 namespace = neutron
 namespace = neutron.agent
 namespace = neutron.db
+namespace = neutron.experimental
 namespace = neutron.extensions
 namespace = nova.auth
 namespace = ironic.auth

neutron/common/experimental.py

@@ -0,0 +1,39 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+
+from oslo_config import cfg
+from oslo_log import log
+
+from neutron.conf import experimental
+
+
+LOG = log.getLogger(__name__)
+
+
+CONF = cfg.CONF
+experimental.register_experimental_opts()
+
+
+def validate_experimental_enabled(feature):
+    try:
+        is_enabled = cfg.CONF.experimental[feature]
+    except cfg.NoSuchOptError:
+        LOG.error("Experimental feature '%s' doesn't exist", feature)
+        raise SystemExit(1)
+    if is_enabled:
+        LOG.warning("Feature '%s' is unsupported and is treated as "
+                    "experimental. Use at your own risk.", feature)
+    else:
+        LOG.error("Feature '%s' is experimental and has to be explicitly "
+                  "enabled in 'cfg.CONF.experimental'", feature)
+        raise SystemExit(1)

neutron/conf/experimental.py

@@ -0,0 +1,29 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+
+from oslo_config import cfg
+
+from neutron._i18n import _
+
+EXPERIMENTAL_CFG_GROUP = 'experimental'
+EXPERIMENTAL_LINUXBRIDGE = 'linuxbridge'
+experimental_opts = [
+    cfg.BoolOpt(EXPERIMENTAL_LINUXBRIDGE,
+                default=False,
+                help=_('Enable execution of the experimental Linuxbridge '
+                       'agent.')),
+]
+
+
+def register_experimental_opts(cfg=cfg.CONF):
+    cfg.register_opts(experimental_opts, EXPERIMENTAL_CFG_GROUP)

neutron/opts.py

@@ -37,6 +37,7 @@ import neutron.conf.db.l3_agentschedulers_db
 import neutron.conf.db.l3_dvr_db
 import neutron.conf.db.l3_gwmode_db
 import neutron.conf.db.l3_hamode_db
+import neutron.conf.experimental
 import neutron.conf.extensions.allowedaddresspairs
 import neutron.conf.extensions.conntrack_helper
 import neutron.conf.plugins.ml2.config
@@ -361,3 +362,11 @@ def list_sriov_agent_opts():
         ('agent',
          neutron.conf.agent.agent_extensions_manager.AGENT_EXT_MANAGER_OPTS)
     ]
+
+
+def list_experimental_opts():
+    return [
+        (neutron.conf.experimental.EXPERIMENTAL_CFG_GROUP,
+         itertools.chain(neutron.conf.experimental.experimental_opts)
+         ),
+    ]

neutron/plugins/ml2/drivers/linuxbridge/mech_driver/mech_linuxbridge.py

@@ -17,6 +17,8 @@ from neutron_lib.api.definitions import portbindings
 from neutron_lib import constants
 
 from neutron.agent import securitygroups_rpc
+from neutron.common import experimental
+from neutron.conf import experimental as c_experimental
 from neutron.plugins.ml2.drivers import mech_agent
 from neutron.services.qos.drivers.linuxbridge import driver as lb_qos_driver
 
@@ -32,6 +34,8 @@ class LinuxbridgeMechanismDriver(mech_agent.SimpleAgentMechanismDriverBase):
     """
 
     def __init__(self):
+        experimental.validate_experimental_enabled(
+            c_experimental.EXPERIMENTAL_LINUXBRIDGE)
         sg_enabled = securitygroups_rpc.is_firewall_enabled()
         vif_details = {portbindings.CAP_PORT_FILTER: sg_enabled,
                        portbindings.VIF_DETAILS_CONNECTIVITY:

neutron/tests/fullstack/resources/config.py

@@ -97,6 +97,9 @@ class NeutronConfigFixture(ConfigFixture):
             'quotas': {
                 'quota_driver': env_desc.quota_driver
             },
+            'experimental': {
+                'linuxbridge': str(env_desc.allow_experimental_linuxbridge)
+            },
         })
 
         if use_local_apipaste:

neutron/tests/fullstack/resources/environment.py

@@ -44,7 +44,8 @@ class EnvironmentDescription(object):
                  dhcp_scheduler_class=None, ml2_extension_drivers=None,
                  api_workers=1,
                  enable_traditional_dhcp=True, local_ip_ext=False,
-                 quota_driver=quota_conf.QUOTA_DB_DRIVER):
+                 quota_driver=quota_conf.QUOTA_DB_DRIVER,
+                 allow_experimental_linuxbridge=True):
         self.network_type = network_type
         self.l2_pop = l2_pop
         self.qos = qos
@@ -72,6 +73,7 @@ class EnvironmentDescription(object):
         if self.local_ip_ext:
             self.service_plugins += ',local_ip'
         self.quota_driver = quota_driver
+        self.allow_experimental_linuxbridge = allow_experimental_linuxbridge
 
     @property
     def tunneling_enabled(self):

neutron/tests/unit/extensions/test_segment.py

@@ -36,6 +36,7 @@ from oslo_config import cfg
 from oslo_utils import uuidutils
 import webob.exc
 
+from neutron.conf import experimental as c_experimental
 from neutron.conf.plugins.ml2 import config as ml2_config
 from neutron.conf.plugins.ml2.drivers import driver_type
 from neutron.db import agents_db
@@ -874,6 +875,11 @@ class TestMl2HostSegmentMappingOVS(HostSegmentMappingTestCase):
 class TestMl2HostSegmentMappingLinuxBridge(TestMl2HostSegmentMappingOVS):
     _mechanism_drivers = ['linuxbridge', 'logger']
 
+    def setUp(self, plugin=None):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(TestMl2HostSegmentMappingLinuxBridge, self).setUp(plugin=plugin)
+
     def _register_agent(self, host, mappings=None, plugin=None):
         helpers.register_linuxbridge_agent(host=host,
                                            bridge_mappings=mappings,

neutron/tests/unit/plugins/ml2/drivers/linuxbridge/mech_driver/test_mech_linuxbridge.py

@@ -15,7 +15,9 @@
 
 from neutron_lib.api.definitions import portbindings
 from neutron_lib import constants
+from oslo_config import cfg
 
+from neutron.conf import experimental as c_experimental
 from neutron.plugins.ml2.drivers.linuxbridge.mech_driver \
     import mech_linuxbridge
 from neutron.tests.unit.plugins.ml2 import _test_mech_agent as base
@@ -65,24 +67,44 @@ class LinuxbridgeMechanismBaseTestCase(base.AgentMechanismBaseTestCase):
 
 class LinuxbridgeMechanismGenericTestCase(LinuxbridgeMechanismBaseTestCase,
                                           base.AgentMechanismGenericTestCase):
-    pass
+
+    def setUp(self):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(LinuxbridgeMechanismGenericTestCase, self).setUp()
 
 
 class LinuxbridgeMechanismLocalTestCase(LinuxbridgeMechanismBaseTestCase,
                                         base.AgentMechanismLocalTestCase):
-    pass
+
+    def setUp(self):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(LinuxbridgeMechanismLocalTestCase, self).setUp()
 
 
 class LinuxbridgeMechanismFlatTestCase(LinuxbridgeMechanismBaseTestCase,
                                        base.AgentMechanismFlatTestCase):
-    pass
+
+    def setUp(self):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(LinuxbridgeMechanismFlatTestCase, self).setUp()
 
 
 class LinuxbridgeMechanismVlanTestCase(LinuxbridgeMechanismBaseTestCase,
                                        base.AgentMechanismVlanTestCase):
-    pass
+
+    def setUp(self):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(LinuxbridgeMechanismVlanTestCase, self).setUp()
 
 
 class LinuxbridgeMechanismGreTestCase(LinuxbridgeMechanismBaseTestCase,
                                       base.AgentMechanismGreTestCase):
-    pass
+
+    def setUp(self):
+        cfg.CONF.set_override(c_experimental.EXPERIMENTAL_LINUXBRIDGE, True,
+                              group=c_experimental.EXPERIMENTAL_CFG_GROUP)
+        super(LinuxbridgeMechanismGreTestCase, self).setUp()

releasenotes/notes/Experimental-features-framework-8c34291b5b0be367.yaml

@@ -0,0 +1,19 @@
+---
+prelude: >
+    Introduce the experimental features framework.
+features:
+  - |
+    Some Neutron features are not supported due to lack of resources or
+    technical expertise to maintain them. As they arise, those features will
+    be marked as experimental by the Neutron core team.
+    Deployers will be able to continue using experimental features by
+    explicitly enabling them in the 'experimental' section of neutron.conf.
+    The ML2 linuxbridge driver is the first feature to be marked as
+    experimental. To continue using it, deployers have to set to True the
+    'linuxbridge' option in the 'experimental' section of neutron.conf.
+deprecations:
+  - |
+    The ML2 linuxbridge agent has been marked as experimental due to lack
+    of resources to maintain it. To continue using it, deployers have to set
+    to True the 'linuxbridge' option in the 'experimental' section of
+    neutron.conf

setup.cfg

@@ -157,6 +157,7 @@ oslo.config.opts =
     neutron.base.agent = neutron.opts:list_base_agent_opts
     neutron.db = neutron.opts:list_db_opts
     neutron.dhcp.agent = neutron.opts:list_dhcp_agent_opts
+    neutron.experimental = neutron.opts:list_experimental_opts
     neutron.extensions = neutron.opts:list_extension_opts
     neutron.l3.agent = neutron.opts:list_l3_agent_opts
     neutron.metadata.agent = neutron.opts:list_metadata_agent_opts

zuul.d/rally.yaml

@@ -10,7 +10,7 @@
         OSPROFILER_COLLECTOR: redis
         OSPROFILER_HMAC_KEYS: "neutron-hmac-key-used-in-zuul-ci"
         Q_ML2_TENANT_NETWORK_TYPE: vxlan
-        Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch,linuxbridge
+        Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch
         Q_AGENT: openvswitch
         KEYSTONE_ADMIN_ENDPOINT: true
       rally_task: rally-jobs/task-neutron.yaml

zuul.d/tempest-multinode.yaml

@@ -178,7 +178,7 @@
         DEFAULT_IMAGE_NAME: cirros-0.5.1-x86_64-uec
         DEFAULT_IMAGE_FILE_NAME: cirros-0.5.1-x86_64-uec.tar.gz
         Q_ML2_TENANT_NETWORK_TYPE: vxlan
-        Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch,linuxbridge
+        Q_ML2_PLUGIN_MECHANISM_DRIVERS: openvswitch
         Q_AGENT: openvswitch
       devstack_plugins:
         neutron: https://opendev.org/openstack/neutron.git