Use network space binding for shared-db relation

To ensure that the charm presents the right IP address for
accessing the MySQL database over the shared-db relation,
ensure that any network space binding provided by the user
is preferred over the default of 'private-address'.

If network spaces is not supported (juju < 2.0), fallback to
using 'private-address'.

Change-Id: Ic5b9f9fe9a275a05feb71ea849af5c8a8dd087de

README.md

@@ -188,9 +188,11 @@ This charm supports the use of Juju Network Spaces, allowing the charm to be bou
 
 API endpoints can be bound to distinct network spaces supporting the network separation of public, internal and admin endpoints.
 
+Access to the underlying MySQL instance can also be bound to a specific space using the shared-db relation.
+
 To use this feature, use the --bind option when deploying the charm:
 
-    juju deploy glance --bind "public=public-space internal=internal-space admin=admin-space"
+    juju deploy glance --bind "public=public-space internal=internal-space admin=admin-space shared-db=internal-space"
 
 alternatively these can also be provided as part of a juju native bundle configuration:
 
@@ -201,6 +203,7 @@ alternatively these can also be provided as part of a juju native bundle configu
         public: public-space
         admin: admin-space
         internal: internal-space
+        shared-db: internal-space
 
 NOTE: Spaces must be configured in the underlying provider prior to attempting to use them.
 

hooks/glance_relations.py

@@ -41,6 +41,7 @@ from charmhelpers.core.hookenv import (
     unit_get,
     UnregisteredHookError,
     status_set,
+    network_get_primary_address,
 )
 from charmhelpers.core.host import (
     # restart_on_change,
@@ -136,7 +137,14 @@ def db_joined():
         sync_db_with_multi_ipv6_addresses(config('database'),
                                           config('database-user'))
     else:
-        host = unit_get('private-address')
+        host = None
+        try:
+            # NOTE: try to use network spaces
+            host = network_get_primary_address('shared-db')
+        except NotImplementedError:
+            # NOTE: fallback to private-address
+            host = unit_get('private-address')
+
         relation_set(database=config('database'),
                      username=config('database-user'),
                      hostname=host)

unit_tests/test_glance_relations.py

@@ -43,6 +43,7 @@ TO_PATCH = [
     'relation_get',
     'service_name',
     'unit_get',
+    'network_get_primary_address',
     # charmhelpers.core.host
     'apt_install',
     'apt_update',
@@ -86,6 +87,7 @@ class GlanceRelationTests(CharmTestCase):
     def setUp(self):
         super(GlanceRelationTests, self).setUp(relations, TO_PATCH)
         self.config.side_effect = self.test_config.get
+        self.network_get_primary_address.side_effect = NotImplementedError
 
     @patch.object(utils, 'git_install_requested')
     def test_install_hook(self, git_requested):
@@ -154,6 +156,17 @@ class GlanceRelationTests(CharmTestCase):
                                              hostname='glance.foohost.com')
         self.unit_get.assert_called_with('private-address')
 
+    def test_db_joined_network_spaces(self):
+        self.network_get_primary_address.side_effect = None
+        self.network_get_primary_address.return_value = '192.168.20.1'
+        self.unit_get.return_value = 'glance.foohost.com'
+        self.is_relation_made.return_value = False
+        relations.db_joined()
+        self.relation_set.assert_called_with(database='glance',
+                                             username='glance',
+                                             hostname='192.168.20.1')
+        self.assertFalse(self.unit_get.called)
+
     def test_db_joined_with_ipv6(self):
         self.test_config.set('prefer-ipv6', True)
         self.is_relation_made.return_value = False