Expose pymemcache's HashClient public params

This patch expose a couple of pymemcache's HashClient public
params that can be useful to configure HA and failover for
clustered memcached servers.

These options can be used in addition of the previously added
retrying mechanismes.

This patch rely on recent changes [1] of dogpile.cache that
aim to expose these options too.

This patch is needed to fix a TLS issue on stable branches introduced by
pymemcache (since train), where if a cluster node disappear the client
will fail without retrying to reconnect or to switch to an other node of
the cluster.

[1] https://gerrit.sqlalchemy.org/c/sqlalchemy/dogpile.cache/+/3528

Partial-Bug: #1959562
Depends-On: https://review.opendev.org/c/openstack/requirements/+/826995
Change-Id: I24fc853db4237c08b87871ddff1b3ced27cc7fce
(cherry picked from commit cb118d04ce)
(cherry picked from commit 55cb199f90)

oslo_cache/_opts.py

@@ -188,6 +188,23 @@ FILE_OPTIONS = {
             'retry_delay',
             default=0,
             help='Number of seconds to sleep between each attempt.'),
+        cfg.IntOpt(
+            'hashclient_retry_attempts',
+            min=1,
+            default=2,
+            help='Amount of times a client should be tried '
+            'before it is marked dead and removed from the pool in '
+            'the HashClient\'s internal mechanisms.'),
+        cfg.FloatOpt(
+            'hashclient_retry_delay',
+            default=1,
+            help='Time in seconds that should pass between '
+            'retry attempts in the HashClient\'s internal mechanisms.'),
+        cfg.FloatOpt(
+            'dead_timeout',
+            default=60,
+            help='Time in seconds before attempting to add a node '
+            'back in the pool in the HashClient\'s internal mechanisms.'),
     ],
 }
 

oslo_cache/core.py

@@ -229,6 +229,12 @@ def _build_cache_config(conf):
             conf.cache.retry_attempts
         conf_dict['%s.arguments.retry_delay' % prefix] = \
             conf.cache.retry_delay
+        conf_dict['%s.arguments.hashclient_retry_attempts' % prefix] = \
+            conf.cache.hashclient_retry_attempts
+        conf_dict['%s.arguments.hashclient_retry_delay' % prefix] = \
+            conf.cache.hashclient_retry_delay
+        conf_dict['%s.arguments.dead_timeout' % prefix] = \
+            conf.cache.dead_timeout
 
     return conf_dict
 

oslo_cache/tests/unit/test_cache_basics.py

@@ -514,6 +514,49 @@ class CacheRegionTest(test_cache.BaseTestCase):
             42
         )
 
+    def test_cache_pymemcache_retry_with_extra_opts(self):
+        """Validate we build a valid config for the retry client."""
+        self.config_fixture.config(group='cache',
+                                   enabled=True,
+                                   config_prefix='test_prefix',
+                                   backend='dogpile.cache.pymemcache',
+                                   enable_retry_client=True,
+                                   retry_attempts=42,
+                                   retry_delay=42,
+                                   hashclient_retry_attempts=100,
+                                   hashclient_retry_delay=100,
+                                   dead_timeout=100)
+
+        config_dict = cache._build_cache_config(self.config_fixture.conf)
+
+        self.assertTrue(
+            self.config_fixture.conf.cache.enable_retry_client)
+
+        self.assertEqual(
+            config_dict['test_prefix.arguments.retry_attempts'],
+            42
+        )
+
+        self.assertEqual(
+            config_dict['test_prefix.arguments.retry_delay'],
+            42
+        )
+
+        self.assertEqual(
+            config_dict['test_prefix.arguments.hashclient_retry_attempts'],
+            100
+        )
+
+        self.assertEqual(
+            config_dict['test_prefix.arguments.hashclient_retry_delay'],
+            100
+        )
+
+        self.assertEqual(
+            config_dict['test_prefix.arguments.dead_timeout'],
+            100
+        )
+
     def test_cache_dictionary_config_builder_flush_on_reconnect_enabled(self):
         """Validate we build a sane dogpile.cache dictionary config."""
         self.config_fixture.config(group='cache',

releasenotes/notes/pymemcache_hashclient_configure-f6f48c5ca38bce47.yaml

@@ -0,0 +1,8 @@
+---
+features:
+  - |
+    Add new options (``hashclient_retry_attempts``, ``hashclient_retry_delay``,
+    ``dead_timeout``) to allow to configure pymemcache's HashClient use
+    through dogpile.cache's pymemcache backend. Those options expose
+    pymemcache params that allow to configure the failover for memcached
+    cluster.

requirements.txt

@@ -2,7 +2,7 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-dogpile.cache>=1.1.4 # BSD
+dogpile.cache>=1.1.5 # BSD
 oslo.config>=8.1.0 # Apache-2.0
 oslo.i18n>=5.0.0 # Apache-2.0
 oslo.log>=4.2.1 # Apache-2.0