Explicitely request cluster version when connecting to etcd via proxy (#1974)

Close https://github.com/zalando/patroni/issues/1971

patroni/dcs/etcd3.py

@@ -262,6 +262,9 @@ class Etcd3Client(AbstractEtcdClientWithFailover):
         return self.api_execute(self.version_prefix + method, self._MPOST, fields)
 
     def authenticate(self):
+        if self._use_proxies and self._cluster_version is None:
+            kwargs = self._prepare_common_parameters(1)
+            self._ensure_version_prefix(self._base_uri, **kwargs)
         if self._cluster_version >= (3, 3) and self.username and self.password:
             logger.info('Trying to authenticate on Etcd...')
             old_token, self._token = self._token, None

tests/test_etcd3.py

@@ -4,8 +4,9 @@ import unittest
 import urllib3
 
 from mock import Mock, patch
-from patroni.dcs.etcd3 import PatroniEtcd3Client, Cluster, Etcd3, Etcd3Error, Etcd3ClientError, RetryFailedError,\
-        InvalidAuthToken, Unavailable, Unknown, UnsupportedEtcdVersion, UserEmpty, AuthFailed, base64_encode
+from patroni.dcs.etcd import DnsCachingResolver
+from patroni.dcs.etcd3 import PatroniEtcd3Client, Cluster, Etcd3Client, Etcd3Error, Etcd3ClientError, RetryFailedError,\
+        InvalidAuthToken, Unavailable, Unknown, UnsupportedEtcdVersion, UserEmpty, AuthFailed, base64_encode, Etcd3
 from threading import Thread
 
 from . import SleepException, MockResponse
@@ -57,6 +58,16 @@ def mock_urlopen(self, method, url, **kwargs):
     return ret
 
 
+class TestEtcd3Client(unittest.TestCase):
+
+    @patch.object(Thread, 'start', Mock())
+    @patch.object(urllib3.PoolManager, 'urlopen', mock_urlopen)
+    def test_authenticate(self):
+        etcd3 = Etcd3Client({'host': '127.0.0.1', 'port': 2379, 'use_proxies': True, 'retry_timeout': 10},
+                            DnsCachingResolver())
+        self.assertIsNotNone(etcd3._cluster_version)
+
+
 class BaseTestEtcd3(unittest.TestCase):
 
     @patch.object(Thread, 'start', Mock())