Send writes to the cluster RW primary

Before this change, DB setup for client applications would occur on
whichever node was the juju leader. This may not be the cluster RW
primary node. This led to Bug #1866164.

This change guarantees that any post-clustering writes get sent to the
cluster RW primary node.

Change-Id: If6beb4450be755a1b204c63759de32d486201202
Closes-Bug: #1866164

src/lib/charm/openstack/mysql_innodb_cluster.py

@@ -413,6 +413,23 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
             upasswdf_template="/var/lib/charm/{}/mysql-{{}}.passwd"
                               .format(ch_core.hookenv.service_name()))
 
+    def get_cluster_rw_db_helper(self):
+        """Get connected RW instance of the MySQLDB8Helper class.
+
+        Connect to the RW cluster primary node and return a DB helper.
+
+        :param self: Self
+        :type self: MySQLInnoDBClusterCharm instance
+        :returns: Instance of MySQLDB8Helper class
+        :rtype: MySQLDB8Helper instance
+        """
+        _helper = self.get_db_helper()
+        _helper.connect(
+            user=self.cluster_user,
+            password=self.cluster_password,
+            host=self.get_cluster_primary_address(nocache=True))
+        return _helper
+
     def create_cluster_user(
             self, cluster_address, cluster_user, cluster_password):
         """Create cluster user and grant permissions in the MySQL DB.
@@ -757,6 +774,32 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
         self._cached_cluster_status = json.loads(output.decode("UTF-8"))
         return self._cached_cluster_status
 
+    def get_cluster_primary_address(self, nocache=False):
+        """Get cluster RW primary address.
+
+        Return cluster.status()['groupInformationSourceMember'] which is the
+        primary R/W node in the cluster.  This node is safe to use for writes
+        to the cluster.
+
+        :param self: Self
+        :type self: MySQLInnoDBClusterCharm instance
+        :param nocache: Do not return cached data
+        :type nocache: Boolean
+        :side effect: Calls self.get_cluster_status
+        :returns: String IP address
+        :rtype: Union[None, str]
+        """
+        if self._cached_cluster_status and not nocache:
+            _status = self._cached_cluster_status
+        else:
+            _status = self.get_cluster_status(nocache=nocache)
+        if not _status:
+            return
+        # Return addresss without port number
+        if ":" in _status['groupInformationSourceMember']:
+            return _status['groupInformationSourceMember'][:-5]
+        return _status['groupInformationSourceMember']
+
     def get_cluster_status_summary(self, nocache=False):
         """Get cluster status summary
 
@@ -944,10 +987,10 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
                 level="DEBUG")
             hosts = [hosts]
 
-        db_helper = self.get_db_helper()
+        rw_helper = self.get_cluster_rw_db_helper()
 
         for host in hosts:
-            password = db_helper.configure_db(host, database, username)
+            password = rw_helper.configure_db(host, database, username)
 
         return password
 
@@ -981,10 +1024,10 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
                 level="DEBUG")
             hosts = [hosts]
 
-        db_helper = self.get_db_helper()
+        rw_helper = self.get_cluster_rw_db_helper()
 
         for host in hosts:
-            password = db_helper.configure_router(host, username)
+            password = rw_helper.configure_router(host, username)
 
         return password
 
@@ -1108,7 +1151,7 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
 
     @tenacity.retry(wait=tenacity.wait_fixed(10),
                     reraise=True,
-                    stop=tenacity.stop_after_delay(5))
+                    stop=tenacity.stop_after_attempt(5))
     def wait_until_connectable(
             self, username=None, password=None, address=None):
         """Wait until MySQL instance is accessible.
@@ -1139,7 +1182,7 @@ class MySQLInnoDBClusterCharm(charms_openstack.charm.OpenStackCharm):
 
     @tenacity.retry(wait=tenacity.wait_fixed(10),
                     reraise=True,
-                    stop=tenacity.stop_after_delay(5))
+                    stop=tenacity.stop_after_attempt(5))
     def wait_until_cluster_available(self):
         """Wait until MySQL InnoDB Cluster is available.
 

unit_tests/test_lib_charm_openstack_mysql_innodb_cluster.py

@@ -399,6 +399,20 @@ class TestMySQLInnoDBClusterCharm(test_utils.PatchHelper):
         self.assertEqual(_helper, midbc.get_db_helper())
         self.MySQL8Helper.assert_called_once()
 
+    def test_get_cluster_rw_db_helper(self):
+        _addr = "10.5.50.41"
+        _helper = mock.MagicMock()
+        midbc = mysql_innodb_cluster.MySQLInnoDBClusterCharm()
+        midbc.get_db_helper = mock.MagicMock()
+        midbc.get_db_helper.return_value = _helper
+        midbc.get_cluster_primary_address = mock.MagicMock()
+        midbc.get_cluster_primary_address.return_value = _addr
+        self.assertEqual(_helper, midbc.get_cluster_rw_db_helper())
+        _helper.connect.assert_called_once_with(
+            user=midbc.cluster_user,
+            password=midbc.cluster_password,
+            host=_addr)
+
     def test_create_cluster_user(self):
         _user = "user"
         _pass = "pass"
@@ -719,8 +733,8 @@ class TestMySQLInnoDBClusterCharm(test_utils.PatchHelper):
         _helper = mock.MagicMock()
         _helper.configure_db.return_value = _pass
         midbc = mysql_innodb_cluster.MySQLInnoDBClusterCharm()
-        midbc.get_db_helper = mock.MagicMock()
-        midbc.get_db_helper.return_value = _helper
+        midbc.get_cluster_rw_db_helper = mock.MagicMock()
+        midbc.get_cluster_rw_db_helper.return_value = _helper
 
         # One host
         self.assertEqual(
@@ -749,8 +763,8 @@ class TestMySQLInnoDBClusterCharm(test_utils.PatchHelper):
         _helper = mock.MagicMock()
         _helper.configure_router.return_value = _pass
         midbc = mysql_innodb_cluster.MySQLInnoDBClusterCharm()
-        midbc.get_db_helper = mock.MagicMock()
-        midbc.get_db_helper.return_value = _helper
+        midbc.get_cluster_rw_db_helper = mock.MagicMock()
+        midbc.get_cluster_rw_db_helper.return_value = _helper
 
         # One host
         self.assertEqual(
@@ -914,6 +928,32 @@ class TestMySQLInnoDBClusterCharm(test_utils.PatchHelper):
         self.assertEqual("OK", midbc.get_cluster_status_summary(nocache=True))
         _status_obj.assert_called_once_with(nocache=True)
 
+    def test_get_cluster_primary_address(self):
+        _addr = "10.5.50.76"
+        _status_dict = {
+            "groupInformationSourceMember": "{}:3360".format(_addr)}
+        _status_obj = mock.MagicMock()
+        _status_obj.return_value = _status_dict
+
+        midbc = mysql_innodb_cluster.MySQLInnoDBClusterCharm()
+        midbc.get_cluster_status = _status_obj
+
+        self.assertEqual(_addr, midbc.get_cluster_primary_address())
+        _status_obj.assert_called_once_with(nocache=False)
+
+        # Cached data
+        _status_obj.reset_mock()
+        midbc._cached_cluster_status = _status_dict
+        self.assertEqual(_addr, midbc.get_cluster_primary_address())
+        _status_obj.assert_not_called()
+
+        # Nocache requested
+        _status_obj.reset_mock()
+        midbc._cached_cluster_status = _status_dict
+        self.assertEqual(
+            _addr, midbc.get_cluster_primary_address(nocache=True))
+        _status_obj.assert_called_once_with(nocache=True)
+
     def test_get_cluster_status_text(self):
         _status_dict = {"defaultReplicaSet": {"statusText": "Text"}}
         _status_obj = mock.MagicMock()