Add support for IGNORE_CLUSTER_ERRORS option

Conditionally ignore failures to `config get cluster` calls against the
configured LOCATION endpoint with the introduction of a `IGNORE_CLUSTER_ERRORS`
option (that defaults to `False`).

Author: hectcastro

README.rst

@@ -36,10 +36,13 @@ Your cache backend should look something like this::
         'default': {
             'BACKEND': 'django_elasticache.memcached.ElastiCache',
             'LOCATION': 'cache-c.draaaf.cfg.use1.cache.amazonaws.com:11211',
+            'OPTIONS' {
+                'IGNORE_CLUSTER_ERRORS': [True,False],
+            },
         }
     }
 
-By the first call to cache it connects to cluster (using LOCATION param),
+By the first call to cache it connects to cluster (using ``LOCATION`` param),
 gets list of all nodes and setup pylibmc client using full
 list of nodes. As result your cache will work with all nodes in cluster and
 automatically detect new nodes in cluster. List of nodes are stored in class-level
@@ -48,6 +51,10 @@ But if you're using gunicorn or mod_wsgi you usually have max_request settings w
 restart process after some count of processed requests, so auto discovery will work
 fine.
 
+The ``IGNORE_CLUSTER_ERRORS`` option is useful when ``LOCATION`` doesn't have support
+for ``config get cluster``. When set to ``True``, and ``config get cluster`` fails,
+it returns a list of a single node with the same endpoint supplied to ``LOCATION``.
+
 Django-elasticache changes default pylibmc params to increase performance.
 
 Another solutions

django_elasticache/cluster_utils.py

@@ -17,7 +17,7 @@ def __init__(self, cmd, response):
             'Unexpected response {} for command {}'.format(response, cmd))
 
 
-def get_cluster_info(host, port, timeout=3):
+def get_cluster_info(host, port, ignore_cluster_errors=False, timeout=3):
     """
     return dict with info about nodes in cluster and current version
     {
@@ -46,7 +46,7 @@ def get_cluster_info(host, port, timeout=3):
     ], timeout)
     client.close()
 
-    if res == b'ERROR\r\n':
+    if res == b'ERROR\r\n' and ignore_cluster_errors:
         return {
             'version': version,
             'nodes': [

django_elasticache/memcached.py

@@ -38,6 +38,9 @@ def __init__(self, server, params):
             raise InvalidCacheBackendError(
                 'Server configuration should be in format IP:port')
 
+        self._ignore_cluster_errors = self._options.get(
+            'IGNORE_CLUSTER_ERRORS', False)
+
     def update_params(self, params):
         """
         update connection params to maximize performance
@@ -51,7 +54,8 @@ def update_params(self, params):
             # set special 'behaviors' pylibmc attributes
             params['OPTIONS'] = {
                 'tcp_nodelay': True,
-                'ketama': True
+                'ketama': True,
+                'IGNORE_CLUSTER_ERRORS': False,
             }
 
     def clear_cluster_nodes_cache(self):
@@ -67,7 +71,8 @@ def get_cluster_nodes(self):
             server, port = self._servers[0].split(':')
             try:
                 self._cluster_nodes_cache = (
-                    get_cluster_info(server, port)['nodes'])
+                    get_cluster_info(server, port,
+                                     self._ignore_cluster_errors)['nodes'])
             except (socket.gaierror, socket.timeout) as err:
                 raise Exception('Cannot connect to cluster {} ({})'.format(
                     self._servers[0], err

tests/test_backend.py

@@ -20,6 +20,7 @@ def test_patch_params():
     eq_(params['BINARY'], True)
     eq_(params['OPTIONS']['tcp_nodelay'], True)
     eq_(params['OPTIONS']['ketama'], True)
+    eq_(params['OPTIONS']['IGNORE_CLUSTER_ERRORS'], False)
 
 
 @raises(Exception)
@@ -47,7 +48,7 @@ def test_split_servers(get_cluster_info):
     }
     backend._lib.Client = Mock()
     assert backend._cache
-    get_cluster_info.assert_called_once_with('h', '0')
+    get_cluster_info.assert_called_once_with('h', '0', False)
     backend._lib.Client.assert_called_once_with(servers)
 
 
@@ -70,7 +71,7 @@ def test_node_info_cache(get_cluster_info):
     eq_(backend._cache.get.call_count, 2)
     eq_(backend._cache.set.call_count, 2)
 
-    get_cluster_info.assert_called_once_with('h', '0')
+    get_cluster_info.assert_called_once_with('h', '0', False)
 
 
 @patch('django.conf.settings', global_settings)

tests/test_protocol.py

@@ -99,14 +99,27 @@ def test_ubuntu_protocol(Telnet):
 
 
 @patch('django_elasticache.cluster_utils.Telnet')
-def test_no_configuration_protocol_support(Telnet):
+def test_no_configuration_protocol_support_with_errors_ignored(Telnet):
     client = Telnet.return_value
     client.read_until.side_effect = TEST_PROTOCOL_4_READ_UNTIL
     client.expect.side_effect = TEST_PROTOCOL_4_EXPECT
-    info = get_cluster_info('test', 0)
+    info = get_cluster_info('test', 0, ignore_cluster_errors=True)
     client.write.assert_has_calls([
         call(b'version\n'),
         call(b'config get cluster\n'),
     ])
     eq_(info['version'], '1.4.34')
     eq_(info['nodes'], ['test:0'])
+
+
+@raises(WrongProtocolData)
+@patch('django_elasticache.cluster_utils.Telnet')
+def test_no_configuration_protocol_support_with_errors(Telnet):
+    client = Telnet.return_value
+    client.read_until.side_effect = TEST_PROTOCOL_4_READ_UNTIL
+    client.expect.side_effect = TEST_PROTOCOL_4_EXPECT
+    get_cluster_info('test', 0, ignore_cluster_errors=False)
+    client.write.assert_has_calls([
+        call(b'version\n'),
+        call(b'config get cluster\n'),
+    ])