Don't reply when we known that client is gone

In case of a broker restart/failover a reply queue can be
unreachable for short period the IncomingMessage.send_reply
will block for 60 seconds in this case or until rabbit recovers.

But in case of the reply queue is unreachable because the
rpc client is really gone, we can have a ton of reply to send
waiting 60 seconds.
This leads to a starvation of connection of the pool
The rpc server take to much time to send reply, other rpc client will
raise TimeoutError because their don't receive their replies in time.

This changes introduces an object cache that stores already known gone
client to not wait 60 seconds and hold a connection of the pool
Keeping 200 last gone rpc client for 1 minute is enough
and doesn't hold to much memory.

This also don't raise anymore a frightening exception when we can't send reply
to the rpc client. But just logging a info about missing exchange and
a warning about unsend reply.

Closes-bug: #1460652

Change-Id: I928b30c9b5f9ee007532ff703e136640b0e8aaf4

5 files changed, 124 insertions, 7 deletions

diff --git a/oslo_messaging/_drivers/amqp.py b/oslo_messaging/_drivers/amqp.py
index a91be1a..7fd3d37 100644
--- a/oslo_messaging/_drivers/amqp.py
+++ b/oslo_messaging/_drivers/amqp.py
@@ -263,3 +263,7 @@ def _add_unique_id(msg):
     """Add unique_id for checking duplicate messages."""
     unique_id = uuid.uuid4().hex
     msg.update({UNIQUE_ID: unique_id})
+
+
+class AMQPDestinationNotFound(Exception):
+    pass
diff --git a/oslo_messaging/_drivers/amqpdriver.py b/oslo_messaging/_drivers/amqpdriver.py
index 3a1d9bb..c1d0f52 100644
--- a/oslo_messaging/_drivers/amqpdriver.py
+++ b/oslo_messaging/_drivers/amqpdriver.py
@@ -19,6 +19,7 @@ import logging
 import threading
 import uuid
 
+import cachetools
 from six import moves
 
 import oslo_messaging
@@ -27,13 +28,15 @@ from oslo_messaging._drivers import base
 from oslo_messaging._drivers import common as rpc_common
 from oslo_messaging._i18n import _
 from oslo_messaging._i18n import _LI
+from oslo_messaging._i18n import _LW
 
 LOG = logging.getLogger(__name__)
 
 
 class AMQPIncomingMessage(base.IncomingMessage):
 
-    def __init__(self, listener, ctxt, message, unique_id, msg_id, reply_q):
+    def __init__(self, listener, ctxt, message, unique_id, msg_id, reply_q,
+                 obsolete_reply_queues):
         super(AMQPIncomingMessage, self).__init__(listener, ctxt,
                                                   dict(message))
 
@@ -42,9 +45,15 @@ class AMQPIncomingMessage(base.IncomingMessage):
         self.reply_q = reply_q
         self.acknowledge_callback = message.acknowledge
         self.requeue_callback = message.requeue
+        self._obsolete_reply_queues = obsolete_reply_queues
 
     def _send_reply(self, conn, reply=None, failure=None,
                     ending=False, log_failure=True):
+        if (self.reply_q and
+            not self._obsolete_reply_queues.reply_q_valid(self.reply_q,
+                                                          self.msg_id)):
+            return
+
         if failure:
             failure = rpc_common.serialize_remote_exception(failure,
                                                             log_failure)
@@ -60,8 +69,15 @@ class AMQPIncomingMessage(base.IncomingMessage):
         # Otherwise use the msg_id for backward compatibility.
         if self.reply_q:
             msg['_msg_id'] = self.msg_id
-            conn.direct_send(self.reply_q, rpc_common.serialize_msg(msg))
+            try:
+                conn.direct_send(self.reply_q, rpc_common.serialize_msg(msg))
+            except rpc_amqp.AMQPDestinationNotFound:
+                self._obsolete_reply_queues.add(self.reply_q, self.msg_id)
         else:
+            # TODO(sileht): look at which version of oslo-incubator rpc
+            # send need this, but I guess this is older than icehouse
+            # if this is icehouse, we can drop this at M
+            # if this is havana, we can drop this now.
             conn.direct_send(self.msg_id, rpc_common.serialize_msg(msg))
 
     def reply(self, reply=None, failure=None, log_failure=True):
@@ -69,6 +85,13 @@ class AMQPIncomingMessage(base.IncomingMessage):
             # NOTE(Alexei_987) not sending reply, if msg_id is empty
             #    because reply should not be expected by caller side
             return
+
+        # NOTE(sileht): return without hold the a connection if possible
+        if (self.reply_q and
+            not self._obsolete_reply_queues.reply_q_valid(self.reply_q,
+                                                          self.msg_id)):
+            return
+
         with self.listener.driver._get_connection(
                 rpc_amqp.PURPOSE_SEND) as conn:
             if self.listener.driver.send_single_reply:
@@ -92,6 +115,51 @@ class AMQPIncomingMessage(base.IncomingMessage):
         self.requeue_callback()
 
 
+class ObsoleteReplyQueuesCache(object):
+    """Cache of reply queue id that doesn't exists anymore.
+
+    NOTE(sileht): In case of a broker restart/failover
+    a reply queue can be unreachable for short period
+    the IncomingMessage.send_reply will block for 60 seconds
+    in this case or until rabbit recovers.
+
+    But in case of the reply queue is unreachable because the
+    rpc client is really gone, we can have a ton of reply to send
+    waiting 60 seconds.
+    This leads to a starvation of connection of the pool
+    The rpc server take to much time to send reply, other rpc client will
+    raise TimeoutError because their don't receive their replies in time.
+
+    This object cache stores already known gone client to not wait 60 seconds
+    and hold a connection of the pool.
+    Keeping 200 last gone rpc client for 1 minute is enough
+    and doesn't hold to much memory.
+    """
+
+    SIZE = 200
+    TTL = 60
+
+    def __init__(self):
+        self._lock = threading.RLock()
+        self._cache = cachetools.TTLCache(self.SIZE, self.TTL)
+
+    def reply_q_valid(self, reply_q, msg_id):
+        if reply_q in self._cache:
+            self._no_reply_log(reply_q, msg_id)
+            return False
+        return True
+
+    def add(self, reply_q, msg_id):
+        with self._lock:
+            self._cache.update({reply_q: msg_id})
+        self._no_reply_log(reply_q, msg_id)
+
+    def _no_reply_log(self, reply_q, msg_id):
+        LOG.warn(_LW("%(reply_queue)s doesn't exists, drop reply to "
+                     "%(msg_id)s"), {'reply_queue': reply_q,
+                                     'msg_id': msg_id})
+
+
 class AMQPListener(base.Listener):
 
     def __init__(self, driver, conn):
@@ -100,6 +168,7 @@ class AMQPListener(base.Listener):
         self.msg_id_cache = rpc_amqp._MsgIdCache()
         self.incoming = []
         self._stopped = threading.Event()
+        self._obsolete_reply_queues = ObsoleteReplyQueuesCache()
 
     def __call__(self, message):
         ctxt = rpc_amqp.unpack_context(self.conf, message)
@@ -116,7 +185,8 @@ class AMQPListener(base.Listener):
                                                  message,
                                                  unique_id,
                                                  ctxt.msg_id,
-                                                 ctxt.reply_q))
+                                                 ctxt.reply_q,
+                                                 self._obsolete_reply_queues))
 
     def poll(self, timeout=None):
         while not self._stopped.is_set():
diff --git a/oslo_messaging/_drivers/impl_rabbit.py b/oslo_messaging/_drivers/impl_rabbit.py
index aa6dc36..2f3fb71 100644
--- a/oslo_messaging/_drivers/impl_rabbit.py
+++ b/oslo_messaging/_drivers/impl_rabbit.py
@@ -1081,8 +1081,17 @@ class Connection(object):
                                  "retrying...") % {
                                      'exchange': exchange.name,
                                      'routing_key': routing_key})
-                    time.sleep(1)
+                    time.sleep(0.25)
                     continue
+                elif exc.code == 404:
+                    msg = _("The exchange %(exchange)s to send to "
+                            "%(routing_key)s still doesn't exist after "
+                            "%(duration)s sec abandonning...") % {
+                                'duration': duration,
+                                'exchange': exchange.name,
+                                'routing_key': routing_key}
+                    LOG.info(msg)
+                    raise rpc_amqp.AMQPDestinationNotFound(msg)
                 raise
 
     def direct_send(self, msg_id, msg):
diff --git a/oslo_messaging/tests/drivers/test_impl_rabbit.py b/oslo_messaging/tests/drivers/test_impl_rabbit.py
index 9b22a1a..ba5b8d3 100644
--- a/oslo_messaging/tests/drivers/test_impl_rabbit.py
+++ b/oslo_messaging/tests/drivers/test_impl_rabbit.py
@@ -355,6 +355,11 @@ class TestSendReceive(test_utils.BaseTestCase):
         ('zero', dict(rx_id=False, reply=0)),
     ]
 
+    _reply_fail = [
+        ('reply_success', dict(reply_failure_404=False)),
+        ('reply_failure', dict(reply_failure_404=True)),
+    ]
+
     _failure = [
         ('success', dict(failure=False)),
         ('failure', dict(failure=True, expected=False)),
@@ -376,11 +381,14 @@ class TestSendReceive(test_utils.BaseTestCase):
         cls.scenarios = testscenarios.multiply_scenarios(cls._n_senders,
                                                          cls._context,
                                                          cls._reply,
+                                                         cls._reply_fail,
                                                          cls._failure,
                                                          cls._timeout,
                                                          cls._reply_ending)
 
     def test_send_receive(self):
+        self.config(kombu_reconnect_timeout=0.5,
+                    group="oslo_messaging_rabbit")
         self.config(heartbeat_timeout_threshold=0,
                     group="oslo_messaging_rabbit")
         self.config(send_single_reply=self.send_single_reply,
@@ -409,16 +417,21 @@ class TestSendReceive(test_utils.BaseTestCase):
 
         def send_and_wait_for_reply(i):
             try:
+                if self.reply_failure_404:
+                    timeout = 0.01
+                else:
+                    timeout = self.timeout
                 replies.append(driver.send(target,
                                            self.ctxt,
                                            {'tx_id': i},
                                            wait_for_reply=True,
-                                           timeout=self.timeout))
+                                           timeout=timeout))
                 self.assertFalse(self.failure)
                 self.assertIsNone(self.timeout)
             except (ZeroDivisionError, oslo_messaging.MessagingTimeout) as e:
                 replies.append(e)
-                self.assertTrue(self.failure or self.timeout is not None)
+                self.assertTrue(self.failure or self.timeout is not None
+                                or self.reply_failure_404)
 
         while len(senders) < self.n_senders:
             senders.append(threading.Thread(target=send_and_wait_for_reply,
@@ -438,6 +451,18 @@ class TestSendReceive(test_utils.BaseTestCase):
         if len(order) > 1:
             order[-1], order[-2] = order[-2], order[-1]
 
+        if self.reply_failure_404:
+            start = time.time()
+            # NOTE(sileht): Simulate a rpc client restart
+            # By returning a ExchangeNotFound when we try to
+            # send reply
+            exc = (driver._reply_q_conn.connection.
+                   connection.channel_errors[0]())
+            exc.code = 404
+            self.useFixture(mockpatch.Patch(
+                'kombu.messaging.Producer.publish',
+                side_effect=exc))
+
         for i in order:
             if self.timeout is None:
                 if self.failure:
@@ -451,11 +476,19 @@ class TestSendReceive(test_utils.BaseTestCase):
                     msgs[i].reply({'rx_id': i})
                 else:
                     msgs[i].reply(self.reply)
+            elif self.reply_failure_404:
+                msgs[i].reply({})
             senders[i].join()
 
+        if self.reply_failure_404:
+            # NOTE(sileht) all reply fail, first take
+            # kombu_reconnect_timeout seconds to fail
+            # next immediatly fail
+            self.assertAlmostEqual(0.5, time.time() - start, 1)
+
         self.assertEqual(len(senders), len(replies))
         for i, reply in enumerate(replies):
-            if self.timeout is not None:
+            if self.timeout is not None or self.reply_failure_404:
                 self.assertIsInstance(reply, oslo_messaging.MessagingTimeout)
             elif self.failure:
                 self.assertIsInstance(reply, ZeroDivisionError)
diff --git a/requirements.txt b/requirements.txt
index d3d5452..9595f6e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -13,6 +13,7 @@ stevedore>=1.5.0 # Apache-2.0
 
 # for jsonutils
 six>=1.9.0
+cachetools>=1.0.0 # MIT License
 
 # FIXME(markmc): remove this when the drivers no longer
 # import eventlet