Add target_session_attrs=read-write to standby_leader primary_conninfo (#2193)

This allows to have multiple hosts in a standby_cluster and ensures that the standby leader follows the main cluster's new leader after a switchover.

Partially addresses #2189

patroni/postgresql/config.py

@@ -486,7 +486,8 @@ class ConfigHandler(object):
         # A list of keywords that can be found in a conninfo string. Follows what is acceptable by libpq
         keywords = ('dbname', 'user', 'passfile' if params.get('passfile') else 'password', 'host', 'port',
                     'sslmode', 'sslcompression', 'sslcert', 'sslkey', 'sslpassword', 'sslrootcert', 'sslcrl',
-                    'sslcrldir', 'application_name', 'krbsrvname', 'gssencmode', 'channel_binding')
+                    'sslcrldir', 'application_name', 'krbsrvname', 'gssencmode', 'channel_binding',
+                    'target_session_attrs')
         if include_dbname:
             params = params.copy()
             if 'dbname' not in params:
@@ -542,6 +543,12 @@ class ConfigHandler(object):
             if use_slots and not (is_remote_master and member.no_replication_slot):
                 primary_slot_name = member.primary_slot_name if is_remote_master else self._postgresql.name
                 recovery_params['primary_slot_name'] = slot_name_from_member_name(primary_slot_name)
+                # We are a standby leader and are using a replication slot. Make sure we connect to
+                # the leader of the main cluster (in case more than one host is specified in the
+                # connstr) by adding 'target_session_attrs=read-write' to primary_conninfo.
+                if is_remote_master and 'target_sesions_attrs' not in primary_conninfo and\
+                        self._postgresql.major_version >= 100000:
+                    primary_conninfo['target_session_attrs'] = 'read-write'
             recovery_params['primary_conninfo'] = primary_conninfo
 
         # standby_cluster config might have different parameters, we want to override them

patroni/postgresql/rewind.py

@@ -154,6 +154,10 @@ class Rewind(object):
         ret = member.conn_kwargs(auth)
         if not ret.get('dbname'):
             ret['dbname'] = self._postgresql.database
+        # Add target_session_attrs in case more than one hostname is specified
+        # (libpq client-side failover) making sure we hit the primary
+        if 'target_session_attrs' not in ret and self._postgresql.major_version >= 100000:
+            ret['target_session_attrs'] = 'read-write'
         return ret
 
     def _check_timeline_and_lsn(self, leader):

tests/test_postgresql.py

@@ -260,8 +260,8 @@ class TestPostgresql(BaseTestPostgresql):
         with patch('patroni.postgresql.config.ConfigHandler.primary_conninfo_params', Mock(return_value=conninfo)):
             mock_get_pg_settings.return_value['recovery_min_apply_delay'][1] = '1'
             self.assertEqual(self.p.config.check_recovery_conf(None), (True, True))
-            mock_get_pg_settings.return_value['primary_conninfo'][1] = 'host=1 passfile='\
-                + re.sub(r'([\'\\ ])', r'\\\1', self.p.config._pgpass)
+            mock_get_pg_settings.return_value['primary_conninfo'][1] = 'host=1 target_session_attrs=read-write'\
+                + ' passfile=' + re.sub(r'([\'\\ ])', r'\\\1', self.p.config._pgpass)
             mock_get_pg_settings.return_value['recovery_min_apply_delay'][1] = '0'
             self.assertEqual(self.p.config.check_recovery_conf(None), (True, True))
             self.p.config.write_recovery_conf({'standby_mode': 'on', 'primary_conninfo': conninfo.copy()})