Set cross_az_attach mode from ncc relation configuration

The cross_az_attach property needs to be configured on the compute
nodes. The policy is set on the ncc service and is propigated to the
compute nodes on the cloud-compute relation. Update the relevant cinder
config setting based on the value provided.

Note, the default value for cross_az_attach is aligned with the nova
default of True.

Closes-Bug: #1899084
Change-Id: I7d00b50acbfe05dfd943a3511126b507fc570aeb

hooks/nova_compute_context.py

@@ -503,6 +503,17 @@ class CloudComputeContext(context.OSContextGenerator):
                                               rid=rid, unit=unit)
         return volume_service
 
+    @property
+    def cross_az_attach(self):
+        # Default to True as that is the nova default
+        cross_az_attach = True
+        for rid in relation_ids('cloud-compute'):
+            for unit in related_units(rid):
+                setting = relation_get('cross_az_attach', rid=rid, unit=unit)
+                if setting is not None:
+                    cross_az_attach = setting
+        return cross_az_attach
+
     @property
     def region(self):
         region = None
@@ -733,6 +744,7 @@ class CloudComputeContext(context.OSContextGenerator):
         vol_service = self.volume_context()
         if vol_service:
             ctxt['volume_service'] = vol_service
+            ctxt['cross_az_attach'] = self.cross_az_attach
 
         if self.restart_trigger():
             ctxt['restart_trigger'] = self.restart_trigger()

templates/parts/section-cinder

@@ -6,4 +6,5 @@ catalog_info = {{ volume_catalog_info }}
 {% if region -%}
 os_region_name = {{ region }}
 {% endif %}
+cross_az_attach = {{ cross_az_attach }}
 {% endif -%}

unit_tests/test_nova_compute_contexts.py

@@ -132,7 +132,32 @@ class NovaComputeContextTests(CharmTestCase):
         self.related_units.return_value = 'nova-cloud-controller/0'
         cloud_compute = context.CloudComputeContext()
         self.test_relation.set({'volume_service': 'cinder'})
-        self.assertEqual({'volume_service': 'cinder'}, cloud_compute())
+        self.assertEqual({'volume_service': 'cinder',
+                          'cross_az_attach': True}, cloud_compute())
+
+    @patch.object(context, '_network_manager')
+    def test_cloud_compute_cross_az_context(self, netman):
+        netman.return_value = None
+        self.relation_ids.return_value = 'cloud-compute:1'
+        self.related_units.return_value = 'nova-cloud-controller/0'
+        cloud_compute = context.CloudComputeContext()
+
+        # Check no cross_az_attach value set, defaults to cross_az_attach=True
+        self.test_relation.set({'volume_service': 'cinder'})
+        self.assertEqual({'volume_service': 'cinder',
+                          'cross_az_attach': True}, cloud_compute())
+
+        # Check that explicit True setting for cross_az_attach
+        self.test_relation.set({'volume_service': 'cinder',
+                                'cross_az_attach': True})
+        self.assertEqual({'volume_service': 'cinder',
+                          'cross_az_attach': True}, cloud_compute())
+
+        # Check false setting for cross_az_attach
+        self.test_relation.set({'volume_service': 'cinder',
+                                'cross_az_attach': False})
+        self.assertEqual({'volume_service': 'cinder',
+                          'cross_az_attach': False}, cloud_compute())
 
     @patch.object(context, '_network_manager')
     def test_cloud_compute_flatdhcp_context(self, netman):