Allow Juju AZ context information to be used

The change adds an option to the charm to use JUJU_AVAILABILITY_ZONE
environment variable set by Juju for the hook environment based on the
underlying provider's availability zone information for a given machine.

This information is used to configure default_availability_zone for nova
and availability_zone for subordinate networking charms.

Change-Id: Idc7112e7fe7b76d15cf9c4896b702b8ffd8c0e8e
Closes-Bug: #1796068

README.md

@@ -43,6 +43,37 @@ different cephx keys and user names.
 See LP Bug [#1671422](https://bugs.launchpad.net/charm-cinder-ceph/+bug/1671422)
 for more information.
 
+Availability Zones
+==================
+
+There are two options to provide default_availability_zone config
+for nova nodes:
+
+  - default-availability-zone
+  - customize-failure-domain
+
+The order of precedence is as follows:
+
+  1. Information from a Juju provider (JUJU_AVAILABILITY_ZONE)
+     if customize-failure-domain is set to True and Juju
+     has set the JUJU_AVAILABILITY_ZONE to a non-empty value;
+  2. The value of default-availability-zone will be used
+     if customize-failure-domain is set to True but no
+     JUJU_AVAILABILITY_ZONE is provided via hook
+     context by the Juju provider;
+  3. Otherwise, the value of default-availability-zone
+     charm option will be used.
+
+The default_availability_zone in Nova affects scheduling if a
+given Nova node was not placed into an aggregate with an
+availability zone present as a property by an operator. Using
+customize-failure-domain is recommended as it provides AZ-aware
+scheduling out of the box if an operator specifies an AZ during
+instance creation.
+
+These options also affect the AZ propagated down to networking
+subordinates which is useful for AZ-aware Neutron agent scheduling.
+
 NFV support
 ===========
 

config.yaml

@@ -373,11 +373,24 @@ options:
       .
       This option determines the availability zone to be used when it is not
       specified in the VM creation request. If this option is not set, the
-      default availability zone 'nova' is used.
+      default availability zone 'nova' is used. If customize-failure-domain
+      is set to True, it will override this option only if an AZ is set by
+      the Juju provider. If JUJU_AVAILABILITY_ZONE is not set, the value
+      specified by this option will be used regardless of
+      customize-failure-domain's setting.
       .
       NOTE: Availability zones must be created manually using the
       'openstack aggregate create' command.
       .
+  customize-failure-domain:
+    type: boolean
+    default: False
+    description: |
+      Juju propagates availability zone information to charms from the
+      underlying machine provider such as MAAS and this option allows the
+      charm to use JUJU_AVAILABILITY_ZONE to set default_availability_zone for
+      Nova nodes. This option overrides the default-availability-zone charm
+      config setting only when the Juju provider sets JUJU_AVAILABILITY_ZONE.
   resume-guests-state-on-host-boot:
     type: boolean
     default: False

hooks/nova_compute_context.py

@@ -51,6 +51,7 @@ from charmhelpers.contrib.network.ip import (
     get_relation_ip,
 )
 
+
 # This is just a label and it must be consistent across
 # nova-compute nodes to support live migration.
 CEPH_SECRET_UUID = '514c9fca-8cbe-11e2-9c52-3bc8c7819472'
@@ -86,6 +87,11 @@ def _network_manager():
     return manager()
 
 
+def _get_availability_zone():
+    from nova_compute_utils import get_availability_zone as get_az
+    return get_az()
+
+
 def _neutron_security_groups():
         '''
         Inspects current cloud-compute relation and determine if nova-c-c has
@@ -722,7 +728,5 @@ class NovaComputeAvailabilityZoneContext(context.OSContextGenerator):
 
     def __call__(self):
         ctxt = {}
-        if config('default-availability-zone'):
-            ctxt['default_availability_zone'] = config(
-                'default-availability-zone')
+        ctxt['default_availability_zone'] = _get_availability_zone()
         return ctxt

hooks/nova_compute_hooks.py

@@ -109,6 +109,7 @@ from nova_compute_utils import (
     configure_local_ephemeral_storage,
     pause_unit_helper,
     resume_unit_helper,
+    get_availability_zone,
 )
 
 from charmhelpers.contrib.network.ip import (
@@ -464,7 +465,7 @@ def update_nrpe_config():
 def neutron_plugin_joined(relid=None, remote_restart=False):
     rel_settings = {
         'hugepage_number': get_hugepage_number(),
-        'default_availability_zone': config('default-availability-zone')
+        'default_availability_zone': get_availability_zone()
     }
     if remote_restart:
         rel_settings['restart-trigger'] = str(uuid.uuid4())

hooks/nova_compute_utils.py

@@ -907,3 +907,10 @@ def configure_local_ephemeral_storage():
     #       storage is never reconfigured by mistake, losing instance disks
     db.set('storage-configured', True)
     db.flush()
+
+
+def get_availability_zone():
+    use_juju_az = config('customize-failure-domain')
+    juju_az = os.environ.get('JUJU_AVAILABILITY_ZONE')
+    return (juju_az if use_juju_az and juju_az
+            else config('default-availability-zone'))

unit_tests/test_nova_compute_contexts.py

@@ -563,3 +563,68 @@ class SerialConsoleContextTests(CharmTestCase):
              'host_uuid': self.host_uuid,
              'force_raw_images': True,
              'reserved_host_memory': 512}, libvirt())
+
+
+class NovaComputeAvailabilityZoneContextTests(CharmTestCase):
+
+    def setUp(self):
+        super(NovaComputeAvailabilityZoneContextTests,
+              self).setUp(context, TO_PATCH)
+        self.os_release.return_value = 'kilo'
+
+    @patch('nova_compute_utils.config')
+    @patch('os.environ.get')
+    def test_availability_zone_no_juju_with_env(self, mock_get,
+                                                mock_config):
+        def environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        mock_get.side_effect = environ_get_side_effect
+
+        def config_side_effect(key):
+            return {
+                'customize-failure-domain': False,
+                'default-availability-zone': 'nova',
+            }[key]
+
+        mock_config.side_effect = config_side_effect
+        az_context = context.NovaComputeAvailabilityZoneContext()
+        self.assertEqual(
+            {'default_availability_zone': 'nova'}, az_context())
+
+    @patch('nova_compute_utils.config')
+    @patch('os.environ.get')
+    def test_availability_zone_no_juju_no_env(self, mock_get,
+                                              mock_config):
+        def environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': '',
+            }[key]
+        mock_get.side_effect = environ_get_side_effect
+
+        def config_side_effect(key):
+            return {
+                'customize-failure-domain': False,
+                'default-availability-zone': 'nova',
+            }[key]
+
+        mock_config.side_effect = config_side_effect
+        az_context = context.NovaComputeAvailabilityZoneContext()
+
+        self.assertEqual(
+            {'default_availability_zone': 'nova'}, az_context())
+
+    @patch('os.environ.get')
+    def test_availability_zone_juju(self, mock_get):
+        def environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        mock_get.side_effect = environ_get_side_effect
+
+        self.config.side_effect = self.test_config.get
+        self.test_config.set('customize-failure-domain', True)
+        az_context = context.NovaComputeAvailabilityZoneContext()
+        self.assertEqual(
+            {'default_availability_zone': 'az1'}, az_context())

unit_tests/test_nova_compute_hooks.py

@@ -542,6 +542,29 @@ class NovaComputeRelationsTests(CharmTestCase):
             **expect_rel_settings
         )
 
+    @patch('os.environ.get')
+    @patch.object(hooks, 'get_hugepage_number')
+    def test_neutron_plugin_joined_relid_juju_az(self,
+                                                 get_hugepage_number,
+                                                 mock_env_get):
+        self.test_config.set('customize-failure-domain', True)
+
+        def environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        mock_env_get.side_effect = environ_get_side_effect
+        get_hugepage_number.return_value = None
+        hooks.neutron_plugin_joined(relid='relid23')
+        expect_rel_settings = {
+            'hugepage_number': None,
+            'default_availability_zone': 'az1',
+        }
+        self.relation_set.assert_called_with(
+            relation_id='relid23',
+            **expect_rel_settings
+        )
+
     @patch.object(hooks, 'get_hugepage_number')
     def test_neutron_plugin_joined_huge(self, get_hugepage_number):
         get_hugepage_number.return_value = 12

unit_tests/test_nova_compute_utils.py

@@ -952,3 +952,55 @@ class NovaComputeUtilsTests(CharmTestCase):
             priority=80
         )
         self.is_block_device.assert_not_called()
+
+    @patch.object(utils.os.environ, 'get')
+    def test_get_az_customize_with_env(self, os_environ_get_mock):
+        self.test_config.set('customize-failure-domain', True)
+        self.test_config.set('default-availability-zone', 'nova')
+
+        def os_environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        os_environ_get_mock.side_effect = os_environ_get_side_effect
+        az = utils.get_availability_zone()
+        self.assertEqual('az1', az)
+
+    @patch.object(utils.os.environ, 'get')
+    def test_get_az_customize_without_env(self, os_environ_get_mock):
+        self.test_config.set('customize-failure-domain', True)
+        self.test_config.set('default-availability-zone', 'mynova')
+
+        def os_environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': '',
+            }[key]
+        os_environ_get_mock.side_effect = os_environ_get_side_effect
+        az = utils.get_availability_zone()
+        self.assertEqual('mynova', az)
+
+    @patch.object(utils.os.environ, 'get')
+    def test_get_az_no_customize_without_env(self, os_environ_get_mock):
+        self.test_config.set('customize-failure-domain', False)
+        self.test_config.set('default-availability-zone', 'nova')
+
+        def os_environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': '',
+            }[key]
+        os_environ_get_mock.side_effect = os_environ_get_side_effect
+        az = utils.get_availability_zone()
+        self.assertEqual('nova', az)
+
+    @patch.object(utils.os.environ, 'get')
+    def test_get_az_no_customize_with_env(self, os_environ_get_mock):
+        self.test_config.set('customize-failure-domain', False)
+        self.test_config.set('default-availability-zone', 'nova')
+
+        def os_environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        os_environ_get_mock.side_effect = os_environ_get_side_effect
+        az = utils.get_availability_zone()
+        self.assertEqual('nova', az)