Failover handling improvements for RedisCluster and Async RedisCluster (#2377)

* Cluster&AsyncCluster: Removed handling of timeouts/connection errors within the cluster loop, fixed "cannot pickle '_thread.lock' object" bug, added client's side failover handling improvements

* Fixed linters

* Type fixes

* Added to CHANGES

* Added getter and setter for the client's retry object and added more tests

* Fixed linters

* Fixed test

* Fixed test_client_kill test

* Changed get_default_backoff to default_backoff, removed retry_on_error and connection_error_retry_attempts from RedisCluster, default retry changed to no retries

* Fixing linters

* Reverting deletion of connection_error_retry_attempts to maintain backward compatibility

* Updating retry object for existing and new connections

* Changed the default value of reinitialize_steps from 10 to 5

* fix review comments

Co-authored-by: Chayim <[email protected]>
Co-authored-by: dvora-h <[email protected]>
Co-authored-by: dvora-h <[email protected]>

Author: 3 people

CHANGES

@@ -24,6 +24,8 @@
     * ClusterPipeline Doesn't Handle ConnectionError for Dead Hosts (#2225)
     * Remove compatibility code for old versions of Hiredis, drop Packaging dependency
     * The `deprecated` library is no longer a dependency
+    * Failover handling improvements for RedisCluster and Async RedisCluster (#2377)
+    * Fixed "cannot pickle '_thread.lock' object" bug (#2354, #2297)
     * Added CredentialsProvider class to support password rotation
     * Enable Lock for asyncio cluster mode
 

redis/__init__.py

@@ -1,5 +1,6 @@
 import sys
 
+from redis.backoff import default_backoff
 from redis.client import Redis, StrictRedis
 from redis.cluster import RedisCluster
 from redis.connection import (
@@ -66,6 +67,7 @@ def int_or_str(value):
     "CredentialProvider",
     "DataError",
     "from_url",
+    "default_backoff",
     "InvalidResponse",
     "PubSubError",
     "ReadOnlyError",

redis/asyncio/__init__.py

@@ -15,6 +15,7 @@
     SentinelManagedSSLConnection,
 )
 from redis.asyncio.utils import from_url
+from redis.backoff import default_backoff
 from redis.exceptions import (
     AuthenticationError,
     AuthenticationWrongNumberOfArgsError,
@@ -43,6 +44,7 @@
     "ConnectionPool",
     "DataError",
     "from_url",
+    "default_backoff",
     "InvalidResponse",
     "PubSubError",
     "ReadOnlyError",

redis/asyncio/client.py

@@ -276,6 +276,13 @@ def get_connection_kwargs(self):
         """Get the connection's key-word arguments"""
         return self.connection_pool.connection_kwargs
 
+    def get_retry(self) -> Optional["Retry"]:
+        return self.get_connection_kwargs().get("retry")
+
+    def set_retry(self, retry: "Retry") -> None:
+        self.get_connection_kwargs().update({"retry": retry})
+        self.connection_pool.set_retry(retry)
+
     def load_external_module(self, funcname, func):
         """
         This function can be used to add externally defined redis modules,

redis/asyncio/cluster.py

@@ -26,6 +26,8 @@
 )
 from redis.asyncio.lock import Lock
 from redis.asyncio.parser import CommandsParser
+from redis.asyncio.retry import Retry
+from redis.backoff import default_backoff
 from redis.client import EMPTY_RESPONSE, NEVER_DECODE, AbstractRedis
 from redis.cluster import (
     PIPELINE_BLOCKED_COMMANDS,
@@ -110,10 +112,10 @@ class RedisCluster(AbstractRedis, AbstractRedisCluster, AsyncRedisClusterCommand
     :param startup_nodes:
         | :class:`~.ClusterNode` to used as a startup node
     :param require_full_coverage:
-        | When set to ``False``: the client will not require a full coverage of the
-          slots. However, if not all slots are covered, and at least one node has
-          ``cluster-require-full-coverage`` set to ``yes``, the server will throw a
-          :class:`~.ClusterDownError` for some key-based commands.
+        | When set to ``False``: the client will not require a full coverage of
+          the slots. However, if not all slots are covered, and at least one node
+          has ``cluster-require-full-coverage`` set to ``yes``, the server will throw
+          a :class:`~.ClusterDownError` for some key-based commands.
         | When set to ``True``: all slots must be covered to construct the cluster
           client. If not all slots are covered, :class:`~.RedisClusterException` will be
           thrown.
@@ -136,7 +138,10 @@ class RedisCluster(AbstractRedis, AbstractRedisCluster, AsyncRedisClusterCommand
           or :class:`~.ConnectionError` or :class:`~.ClusterDownError` are encountered
     :param connection_error_retry_attempts:
         | Number of times to retry before reinitializing when :class:`~.TimeoutError`
-          or :class:`~.ConnectionError` are encountered
+          or :class:`~.ConnectionError` are encountered.
+          The default backoff strategy will be set if Retry object is not passed (see
+          default_backoff in backoff.py). To change it, pass a custom Retry object
+          using the "retry" keyword.
     :param max_connections:
         | Maximum number of connections per node. If there are no free connections & the
           maximum number of connections are already created, a
@@ -214,9 +219,9 @@ def __init__(
         startup_nodes: Optional[List["ClusterNode"]] = None,
         require_full_coverage: bool = True,
         read_from_replicas: bool = False,
-        reinitialize_steps: int = 10,
+        reinitialize_steps: int = 5,
         cluster_error_retry_attempts: int = 3,
-        connection_error_retry_attempts: int = 5,
+        connection_error_retry_attempts: int = 3,
         max_connections: int = 2**31,
         # Client related kwargs
         db: Union[str, int] = 0,
@@ -235,6 +240,8 @@ def __init__(
         socket_keepalive: bool = False,
         socket_keepalive_options: Optional[Mapping[int, Union[int, bytes]]] = None,
         socket_timeout: Optional[float] = None,
+        retry: Optional["Retry"] = None,
+        retry_on_error: Optional[List[Exception]] = None,
         # SSL related kwargs
         ssl: bool = False,
         ssl_ca_certs: Optional[str] = None,
@@ -282,6 +289,7 @@ def __init__(
             "socket_keepalive": socket_keepalive,
             "socket_keepalive_options": socket_keepalive_options,
             "socket_timeout": socket_timeout,
+            "retry": retry,
         }
 
         if ssl:
@@ -302,6 +310,18 @@ def __init__(
             # Call our on_connect function to configure READONLY mode
             kwargs["redis_connect_func"] = self.on_connect
 
+        self.retry = retry
+        if retry or retry_on_error or connection_error_retry_attempts > 0:
+            # Set a retry object for all cluster nodes
+            self.retry = retry or Retry(
+                default_backoff(), connection_error_retry_attempts
+            )
+            if not retry_on_error:
+                # Default errors for retrying
+                retry_on_error = [ConnectionError, TimeoutError]
+            self.retry.update_supported_errors(retry_on_error)
+            kwargs.update({"retry": self.retry})
+
         kwargs["response_callbacks"] = self.__class__.RESPONSE_CALLBACKS.copy()
         self.connection_kwargs = kwargs
 
@@ -323,7 +343,6 @@ def __init__(
         self.reinitialize_steps = reinitialize_steps
         self.cluster_error_retry_attempts = cluster_error_retry_attempts
         self.connection_error_retry_attempts = connection_error_retry_attempts
-
         self.reinitialize_counter = 0
         self.commands_parser = CommandsParser()
         self.node_flags = self.__class__.NODE_FLAGS.copy()
@@ -481,6 +500,16 @@ def get_connection_kwargs(self) -> Dict[str, Optional[Any]]:
         """Get the kwargs passed to :class:`~redis.asyncio.connection.Connection`."""
         return self.connection_kwargs
 
+    def get_retry(self) -> Optional["Retry"]:
+        return self.retry
+
+    def set_retry(self, retry: "Retry") -> None:
+        self.retry = retry
+        for node in self.get_nodes():
+            node.connection_kwargs.update({"retry": retry})
+            for conn in node._connections:
+                conn.retry = retry
+
     def set_response_callback(self, command: str, callback: ResponseCallbackT) -> None:
         """Set a custom response callback."""
         self.response_callbacks[command] = callback
@@ -618,9 +647,11 @@ async def execute_command(self, *args: EncodableT, **kwargs: Any) -> Any:
         if passed_targets and not self._is_node_flag(passed_targets):
             target_nodes = self._parse_target_nodes(passed_targets)
             target_nodes_specified = True
-            retry_attempts = 1
+            retry_attempts = 0
 
-        for _ in range(retry_attempts):
+        # Add one for the first execution
+        execute_attempts = 1 + retry_attempts
+        for _ in range(execute_attempts):
             if self._initialize:
                 await self.initialize()
             try:
@@ -658,25 +689,21 @@ async def execute_command(self, *args: EncodableT, **kwargs: Any) -> Any:
                         )
                     return dict(zip(keys, values))
             except Exception as e:
-                if type(e) in self.__class__.ERRORS_ALLOW_RETRY:
-                    # The nodes and slots cache were reinitialized.
+                if retry_attempts > 0 and type(e) in self.__class__.ERRORS_ALLOW_RETRY:
+                    # The nodes and slots cache were should be reinitialized.
                     # Try again with the new cluster setup.
-                    exception = e
+                    retry_attempts -= 1
+                    continue
                 else:
-                    # All other errors should be raised.
-                    raise
-
-        # If it fails the configured number of times then raise exception back
-        # to caller of this method
-        raise exception
+                    # raise the exception
+                    raise e
 
     async def _execute_command(
         self, target_node: "ClusterNode", *args: Union[KeyT, EncodableT], **kwargs: Any
     ) -> Any:
         asking = moved = False
         redirect_addr = None
         ttl = self.RedisClusterRequestTTL
-        connection_error_retry_counter = 0
 
         while ttl > 0:
             ttl -= 1
@@ -695,25 +722,18 @@ async def _execute_command(
                     moved = False
 
                 return await target_node.execute_command(*args, **kwargs)
-            except BusyLoadingError:
+            except (BusyLoadingError, MaxConnectionsError):
+                raise
+            except (ConnectionError, TimeoutError):
+                # Connection retries are being handled in the node's
+                # Retry object.
+                # Remove the failed node from the startup nodes before we try
+                # to reinitialize the cluster
+                self.nodes_manager.startup_nodes.pop(target_node.name, None)
+                # Hard force of reinitialize of the node/slots setup
+                # and try again with the new setup
+                await self.close()
                 raise
-            except (ConnectionError, TimeoutError) as e:
-                # Give the node 0.25 seconds to get back up and retry again with the
-                # same node and configuration. After the defined number of attempts, try
-                # to reinitialize the cluster and try again.
-                connection_error_retry_counter += 1
-                if (
-                    connection_error_retry_counter
-                    < self.connection_error_retry_attempts
-                ):
-                    await asyncio.sleep(0.25)
-                else:
-                    if isinstance(e, MaxConnectionsError):
-                        raise
-                    # Hard force of reinitialize of the node/slots setup
-                    # and try again with the new setup
-                    await self.close()
-                    raise
             except ClusterDownError:
                 # ClusterDownError can occur during a failover and to get
                 # self-healed, we will try to reinitialize the cluster layout
@@ -1145,26 +1165,11 @@ async def initialize(self) -> None:
                     )
                 cluster_slots = await startup_node.execute_command("CLUSTER SLOTS")
                 startup_nodes_reachable = True
-            except (ConnectionError, TimeoutError) as e:
+            except Exception as e:
+                # Try the next startup node.
+                # The exception is saved and raised only if we have no more nodes.
                 exception = e
                 continue
-            except ResponseError as e:
-                # Isn't a cluster connection, so it won't parse these
-                # exceptions automatically
-                message = e.__str__()
-                if "CLUSTERDOWN" in message or "MASTERDOWN" in message:
-                    continue
-                else:
-                    raise RedisClusterException(
-                        'ERROR sending "cluster slots" command to redis '
-                        f"server: {startup_node}. error: {message}"
-                    )
-            except Exception as e:
-                message = e.__str__()
-                raise RedisClusterException(
-                    'ERROR sending "cluster slots" command to redis '
-                    f"server {startup_node.name}. error: {message}"
-                )
 
             # CLUSTER SLOTS command results in the following output:
             # [[slot_section[from_slot,to_slot,master,replica1,...,replicaN]]]
@@ -1245,8 +1250,8 @@ async def initialize(self) -> None:
 
         if not startup_nodes_reachable:
             raise RedisClusterException(
-                "Redis Cluster cannot be connected. Please provide at least "
-                "one reachable node. "
+                f"Redis Cluster cannot be connected. Please provide at least "
+                f"one reachable node: {str(exception)}"
             ) from exception
 
         # Check if the slots are not fully covered

redis/asyncio/connection.py

@@ -497,7 +497,7 @@ def __init__(
             retry_on_error.append(socket.timeout)
             retry_on_error.append(asyncio.TimeoutError)
         self.retry_on_error = retry_on_error
-        if retry_on_error:
+        if retry or retry_on_error:
             if not retry:
                 self.retry = Retry(NoBackoff(), 1)
             else:
@@ -1445,6 +1445,12 @@ async def disconnect(self, inuse_connections: bool = True):
             if exc:
                 raise exc
 
+    def set_retry(self, retry: "Retry") -> None:
+        for conn in self._available_connections:
+            conn.retry = retry
+        for conn in self._in_use_connections:
+            conn.retry = retry
+
 
 class BlockingConnectionPool(ConnectionPool):
     """

redis/backoff.py

@@ -1,6 +1,11 @@
 import random
 from abc import ABC, abstractmethod
 
+# Maximum backoff between each retry in seconds
+DEFAULT_CAP = 0.512
+# Minimum backoff between each retry in seconds
+DEFAULT_BASE = 0.008
+
 
 class AbstractBackoff(ABC):
     """Backoff interface"""
@@ -40,7 +45,7 @@ def __init__(self):
 class ExponentialBackoff(AbstractBackoff):
     """Exponential backoff upon failure"""
 
-    def __init__(self, cap, base):
+    def __init__(self, cap=DEFAULT_CAP, base=DEFAULT_BASE):
         """
         `cap`: maximum backoff time in seconds
         `base`: base backoff time in seconds
@@ -55,7 +60,7 @@ def compute(self, failures):
 class FullJitterBackoff(AbstractBackoff):
     """Full jitter backoff upon failure"""
 
-    def __init__(self, cap, base):
+    def __init__(self, cap=DEFAULT_CAP, base=DEFAULT_BASE):
         """
         `cap`: maximum backoff time in seconds
         `base`: base backoff time in seconds
@@ -70,7 +75,7 @@ def compute(self, failures):
 class EqualJitterBackoff(AbstractBackoff):
     """Equal jitter backoff upon failure"""
 
-    def __init__(self, cap, base):
+    def __init__(self, cap=DEFAULT_CAP, base=DEFAULT_BASE):
         """
         `cap`: maximum backoff time in seconds
         `base`: base backoff time in seconds
@@ -86,7 +91,7 @@ def compute(self, failures):
 class DecorrelatedJitterBackoff(AbstractBackoff):
     """Decorrelated jitter backoff upon failure"""
 
-    def __init__(self, cap, base):
+    def __init__(self, cap=DEFAULT_CAP, base=DEFAULT_BASE):
         """
         `cap`: maximum backoff time in seconds
         `base`: base backoff time in seconds
@@ -103,3 +108,7 @@ def compute(self, failures):
         temp = random.uniform(self._base, max_backoff)
         self._previous_backoff = min(self._cap, temp)
         return self._previous_backoff
+
+
+def default_backoff():
+    return EqualJitterBackoff()

redis/client.py

@@ -26,6 +26,7 @@
     WatchError,
 )
 from redis.lock import Lock
+from redis.retry import Retry
 from redis.utils import safe_str, str_if_bytes
 
 SYM_EMPTY = b""
@@ -1047,6 +1048,13 @@ def get_connection_kwargs(self):
         """Get the connection's key-word arguments"""
         return self.connection_pool.connection_kwargs
 
+    def get_retry(self) -> Optional["Retry"]:
+        return self.get_connection_kwargs().get("retry")
+
+    def set_retry(self, retry: "Retry") -> None:
+        self.get_connection_kwargs().update({"retry": retry})
+        self.connection_pool.set_retry(retry)
+
     def set_response_callback(self, command, callback):
         """Set a custom Response Callback"""
         self.response_callbacks[command] = callback