Exhaust VLAN allocations in physnet order

When an operator configured multiple network VLAN ranges, we
had no guarantee that we would actually allocate in the order
specified like we do with segmentation types. In *most* cases,
the natural database order would be that the returned available
segment IDs would come back in the order of the physnets because
the sync_allocations code inserted them in that order. So it
became something some deployments would rely on and operators
would get a surprise when suddenly an allocation would happen
from the later physnets while many VLANs were still available
in the first one.

This patch just strictly makes allocation attempts in the order
of the network_vlan_ranges so operators are always guaranteed that
the later physnets will not automatically be allocated from unless
the earlier physnets are exhausted.

Change-Id: I14ca9b7e1141199f3ec221184fbbe156f1f9e18b

neutron/plugins/common/utils.py

@@ -16,6 +16,7 @@
 Common utilities and helper functions for OpenStack Networking Plugins.
 """
 
+import collections
 import contextlib
 import hashlib
 
@@ -131,7 +132,7 @@ def parse_network_vlan_range(network_vlan_range):
 
 def parse_network_vlan_ranges(network_vlan_ranges_cfg_entries):
     """Interpret a list of strings as network[:vlan_begin:vlan_end] entries."""
-    networks = {}
+    networks = collections.OrderedDict()
     for entry in network_vlan_ranges_cfg_entries:
         network, vlan_range = parse_network_vlan_range(entry)
         if vlan_range:

neutron/plugins/ml2/drivers/type_vlan.py

@@ -196,8 +196,12 @@ class VlanTypeDriver(helpers.SegmentTypeDriver):
                 api.MTU: self.get_mtu(alloc.physical_network)}
 
     def allocate_tenant_segment(self, context):
-        alloc = self.allocate_partially_specified_segment(context)
-        if not alloc:
+        for physnet in self.network_vlan_ranges:
+            alloc = self.allocate_partially_specified_segment(
+                context, physical_network=physnet)
+            if alloc:
+                break
+        else:
             return
         return {api.NETWORK_TYPE: p_const.TYPE_VLAN,
                 api.PHYSICAL_NETWORK: alloc.physical_network,

neutron/tests/unit/plugins/ml2/drivers/test_type_vlan.py

@@ -259,3 +259,36 @@ class VlanTypeTest(testlib_api.SqlTestCase):
                 "No vlan_id %(vlan_id)s found on physical network "
                 "%(physical_network)s",
                 {'vlan_id': 101, 'physical_network': PROVIDER_NET})
+
+
+class VlanTypeAllocationTest(testlib_api.SqlTestCase):
+
+    def test_allocate_tenant_segment_in_order_of_config(self):
+        ranges = NETWORK_VLAN_RANGES + ['phys_net3:20:30']
+        config.cfg.CONF.set_override('network_vlan_ranges',
+                                     ranges,
+                                     group='ml2_type_vlan')
+        driver = type_vlan.VlanTypeDriver()
+        driver.physnet_mtus = []
+        driver._sync_vlan_allocations()
+        # swap config order from DB order after sync has happened to
+        # ensure config order is followed and not DB order
+        config.cfg.CONF.set_override('network_vlan_ranges',
+                                     list(reversed(ranges)),
+                                     group='ml2_type_vlan')
+        driver._parse_network_vlan_ranges()
+        ctx = context.Context()
+        for vlan in range(11):
+            # all of physnet3 should be exhausted first
+            self.assertEqual(
+                {'network_type': 'vlan', 'physical_network': 'phys_net3',
+                 'segmentation_id': mock.ANY, 'mtu': 1500},
+                driver.allocate_tenant_segment(ctx))
+        for vlan in range(10):
+            # then physnet2
+            self.assertEqual(
+                {'network_type': 'vlan', 'physical_network': 'phys_net2',
+                 'segmentation_id': mock.ANY, 'mtu': 1500},
+                driver.allocate_tenant_segment(ctx))
+        # then nothing
+        self.assertFalse(driver.allocate_tenant_segment(ctx))