Add support for when cluster endpoint is not available

Modify `get_cluster_info` to include a timeout (defaults to 3 seconds) and
gracefully degrade when the ElastiCache cluster configuration endpoint isn't
available by returning the provided `host` and `port` in the `nodes` list.

I also added an additional test to the protocol test suite to cover the
additional functionality.

Author: hectcastro

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):
+def get_cluster_info(host, port, timeout=3):
     """
     return dict with info about nodes in cluster and current version
     {
@@ -30,7 +30,7 @@ def get_cluster_info(host, port):
     """
     client = Telnet(host, int(port))
     client.write(b'version\n')
-    res = client.read_until(b'\r\n').strip()
+    res = client.read_until(b'\r\n', timeout).strip()
     version_list = res.split(b' ')
     if len(version_list) not in [2, 3] or version_list[0] != b'VERSION':
         raise WrongProtocolData('version', res)
@@ -40,8 +40,18 @@ def get_cluster_info(host, port):
     else:
         cmd = b'get AmazonElastiCache:cluster\n'
     client.write(cmd)
-    res = client.read_until(b'\n\r\nEND\r\n')
+    res = client.read_until(b'\n\r\nEND\r\n', timeout)
     client.close()
+
+    if res == 'ERROR\r\n':
+        return {
+            'version': version,
+            'nodes': [
+                '{}:{}'.format(smart_text(host),
+                               smart_text(port))
+            ]
+        }
+
     ls = list(filter(None, re.compile(br'\r?\n').split(res)))
     if len(ls) != 4:
         raise WrongProtocolData(cmd, res)

tests/test_protocol.py

@@ -23,6 +23,11 @@
     b'CONFIG cluster 0 138\r\n1\nhost|ip|port host||port\n\r\nEND\r\n',
 ]
 
+TEST_PROTOCOL_4 = [
+    b'VERSION 1.4.34',
+    b'ERROR\r\n',
+]
+
 
 @patch('django_elasticache.cluster_utils.Telnet')
 def test_happy_path(Telnet):
@@ -75,3 +80,16 @@ def test_ubuntu_protocol(Telnet):
         call(b'version\n'),
         call(b'config get cluster\n'),
     ])
+
+
+@patch('django_elasticache.cluster_utils.Telnet')
+def test_no_configuration_protocol_support(Telnet):
+    client = Telnet.return_value
+    client.read_until.side_effect = TEST_PROTOCOL_4
+    info = get_cluster_info('test', 0)
+    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'])