Add ngs_manage_vlans configuration

This allows operators to opt out of NGS adding or removing VLANs
from switches. This is useful when not all switch configuration
is being managed by Networking Generic Switch.

A similar concenpt is already supported by ansible-networking:
https://opendev.org/x/networking-ansible/src/commit/6f56fd45425141e5435884d2d0cf88ee96a887c6/etc/neutron/plugins/ml2/ml2_conf_ansible.ini.sample

Co-Authored-By: Michal Nasiadka <mnasiadka@gmail.com>

Change-Id: I271263a349d6cccd0fe9980e10b1b8d5fd86716e

Author: JohnGarbutt

doc/source/configuration.rst

@@ -244,3 +244,25 @@ For example::
 
 Some switches have issues assigning VLANs a name that starts with a number,
 and this configuration option can be used to avoid this.
+
+Manage VLANs
+============
+
+By default, on network creation VLANs are added to all switches. In a similar
+way, VLANs are removed when it seems they are no longer required.
+However, in some cases only a subset of the ports are managed by Neutron.
+In a similar way, when multiple switches are used, it is very common that
+the network administrator restricts the VLANs allowed. In these cases, there
+is little utility in adding and removing vlans on the switches. This process
+takes time, so not doing this can speed up a number of common operations.
+A particular case where this can cause problems is when a VLAN used for
+the switch management interface, or any other port not managed by Neutron,
+is removed by this Neutron driver.
+
+To stop networking generic switch trying to add or remove VLANs on the switch
+administrator are expected to pre-add all enabled VLANs. Once those VLANs are
+preconfigured on the switch, you can use the following configuration to stop
+networking generic switch adding or removing any VLANs::
+
+    [genericswitch:device-hostname]
+    ngs_manage_vlans = False

networking_generic_switch/devices/__init__.py

@@ -40,6 +40,8 @@
     # String format for network name to configure on switches.
     # Accepts {network_id} and {segmentation_id} formatting options.
     {'name': 'ngs_network_name_format', 'default': '{network_id}'},
+    # If false, ngs will not add and delete VLANs from switches
+    {'name': 'ngs_manage_vlans', 'default': True},
 ]
 
 
@@ -130,6 +132,10 @@ def _get_network_name(self, network_id, segmentation_id):
         return network_name_format.format(network_id=network_id,
                                           segmentation_id=segmentation_id)
 
+    def _do_vlan_management(self):
+        """Check if drivers should add and remove VLANs from switches."""
+        return strutils.bool_from_string(self.ngs_config['ngs_manage_vlans'])
+
     @abc.abstractmethod
     def add_network(self, segmentation_id, network_id):
         pass

networking_generic_switch/devices/netmiko_devices/__init__.py

@@ -200,6 +200,10 @@ def send_commands_to_device(self, cmd_set):
 
     @check_output('add network')
     def add_network(self, segmentation_id, network_id):
+        if not self._do_vlan_management():
+            LOG.info(f"Skipping add network for {segmentation_id}")
+            return ""
+
         # NOTE(zhenguo): Remove dashes from uuid as on most devices 32 chars
         # is the max length of vlan name.
         network_id = uuid.UUID(network_id).hex
@@ -218,6 +222,10 @@ def add_network(self, segmentation_id, network_id):
 
     @check_output('delete network')
     def del_network(self, segmentation_id, network_id):
+        if not self._do_vlan_management():
+            LOG.info(f"Skipping delete network for {segmentation_id}")
+            return ""
+
         # NOTE(zhenguo): Remove dashes from uuid as on most devices 32 chars
         # is the max length of vlan name.
         network_id = uuid.UUID(network_id).hex

networking_generic_switch/tests/unit/netmiko/test_netmiko_base.py

@@ -67,6 +67,17 @@ def test_add_network_with_trunk_ports(self, m_check, m_sctd):
         m_sctd.assert_called_with([])
         m_check.assert_called_once_with('fake output', 'add network')
 
+    @mock.patch('networking_generic_switch.devices.netmiko_devices.'
+                'NetmikoSwitch.send_commands_to_device',
+                return_value='fake output')
+    @mock.patch('networking_generic_switch.devices.netmiko_devices.'
+                'NetmikoSwitch.check_output')
+    def test_add_network_with_no_manage_vlans(self, m_check, m_sctd):
+        switch = self._make_switch_device({'ngs_manage_vlans': False})
+        switch.add_network(22, '0ae071f5-5be9-43e4-80ea-e41fefe85b21')
+        self.assertFalse(m_sctd.called)
+        m_check.assert_called_once_with('', 'add network')
+
     @mock.patch('networking_generic_switch.devices.netmiko_devices.'
                 'NetmikoSwitch.send_commands_to_device',
                 return_value='fake output')
@@ -88,6 +99,17 @@ def test_del_network_with_trunk_ports(self, m_check, m_sctd):
         m_sctd.assert_called_with([])
         m_check.assert_called_once_with('fake output', 'delete network')
 
+    @mock.patch('networking_generic_switch.devices.netmiko_devices.'
+                'NetmikoSwitch.send_commands_to_device',
+                return_value='fake output')
+    @mock.patch('networking_generic_switch.devices.netmiko_devices.'
+                'NetmikoSwitch.check_output')
+    def test_del_network_with_no_manage_vlans(self, m_check, m_sctd):
+        switch = self._make_switch_device({'ngs_manage_vlans': False})
+        switch.del_network(22, '0ae071f5-5be9-43e4-80ea-e41fefe85b21')
+        self.assertFalse(m_sctd.called)
+        m_check.assert_called_once_with('', 'delete network')
+
     @mock.patch('networking_generic_switch.devices.netmiko_devices.'
                 'NetmikoSwitch.send_commands_to_device',
                 return_value='fake output')

releasenotes/notes/manage-vlans-c75e4c2e9b9b3403.yaml

@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    New per switch `ngs_manage_vlans` option. It defaults to True, but can
+    be set to False so that no VLANs are added or removed on that switch.
+    This is useful when not all ports on the switch are managed by Neutron.