KIP-144: Exponential backoff for broker reconnections (#1124)

1 files changed, 37 insertions, 3 deletions

diff --git a/kafka/conn.py b/kafka/conn.py
index 12bd08d..f118345 100644
--- a/kafka/conn.py
+++ b/kafka/conn.py
@@ -5,7 +5,7 @@ import copy
 import errno
 import logging
 import io
-from random import shuffle
+from random import shuffle, uniform
 import socket
 import time
 import traceback
@@ -78,6 +78,14 @@ class BrokerConnection(object):
         reconnect_backoff_ms (int): The amount of time in milliseconds to
             wait before attempting to reconnect to a given host.
             Default: 50.
+        reconnect_backoff_max_ms (int): The maximum amount of time in
+            milliseconds to wait when reconnecting to a broker that has
+            repeatedly failed to connect. If provided, the backoff per host
+            will increase exponentially for each consecutive connection
+            failure, up to this maximum. To avoid connection storms, a
+            randomization factor of 0.2 will be applied to the backoff
+            resulting in a random range between 20% below and 20% above
+            the computed value. Default: 1000.
         request_timeout_ms (int): Client request timeout in milliseconds.
             Default: 40000.
         max_in_flight_requests_per_connection (int): Requests are pipelined
@@ -140,6 +148,7 @@ class BrokerConnection(object):
         'node_id': 0,
         'request_timeout_ms': 40000,
         'reconnect_backoff_ms': 50,
+        'reconnect_backoff_max_ms': 1000,
         'max_in_flight_requests_per_connection': 5,
         'receive_buffer_bytes': None,
         'send_buffer_bytes': None,
@@ -199,6 +208,7 @@ class BrokerConnection(object):
                 assert self.config['sasl_plain_password'] is not None, 'sasl_plain_password required for PLAIN sasl'
 
         self.state = ConnectionStates.DISCONNECTED
+        self._reset_reconnect_backoff()
         self._sock = None
         self._ssl_context = None
         if self.config['ssl_context'] is not None:
@@ -305,6 +315,7 @@ class BrokerConnection(object):
                 else:
                     log.debug('%s: Connection complete.', self)
                     self.state = ConnectionStates.CONNECTED
+                    self._reset_reconnect_backoff()
                 self.config['state_change_callback'](self)
 
             # Connection failed
@@ -340,6 +351,7 @@ class BrokerConnection(object):
                 log.info('%s: Authenticated as %s', self, self.config['sasl_plain_username'])
                 log.debug('%s: Connection complete.', self)
                 self.state = ConnectionStates.CONNECTED
+                self._reset_reconnect_backoff()
                 self.config['state_change_callback'](self)
 
         return self.state
@@ -475,11 +487,19 @@ class BrokerConnection(object):
         re-establish a connection yet
         """
         if self.state is ConnectionStates.DISCONNECTED:
-            backoff = self.config['reconnect_backoff_ms'] / 1000.0
-            if time.time() < self.last_attempt + backoff:
+            if time.time() < self.last_attempt + self._reconnect_backoff:
                 return True
         return False
 
+    def connection_delay(self):
+        time_waited_ms = time.time() - (self.last_attempt or 0)
+        if self.state is ConnectionStates.DISCONNECTED:
+            return max(self._reconnect_backoff - time_waited_ms, 0)
+        elif self.connecting():
+            return 0
+        else:
+            return 999999999
+
     def connected(self):
         """Return True iff socket is connected."""
         return self.state is ConnectionStates.CONNECTED
@@ -495,6 +515,19 @@ class BrokerConnection(object):
         """Return True iff socket is closed"""
         return self.state is ConnectionStates.DISCONNECTED
 
+    def _reset_reconnect_backoff(self):
+        self._failures = 0
+        self._reconnect_backoff = self.config['reconnect_backoff_ms'] / 1000.0
+
+    def _update_reconnect_backoff(self):
+        if self.config['reconnect_backoff_max_ms'] > self.config['reconnect_backoff_ms']:
+            self._failures += 1
+            self._reconnect_backoff = self.config['reconnect_backoff_ms'] * 2 ** (self._failures - 1)
+            self._reconnect_backoff = min(self._reconnect_backoff, self.config['reconnect_backoff_max_ms'])
+            self._reconnect_backoff *= uniform(0.8, 1.2)
+            self._reconnect_backoff /= 1000.0
+            log.debug('%s: reconnect backoff %s after %s failures', self, self._reconnect_backoff, self._failures)
+
     def close(self, error=None):
         """Close socket and fail all in-flight-requests.
 
@@ -512,6 +545,7 @@ class BrokerConnection(object):
         log.info('%s: Closing connection. %s', self, error or '')
         self.state = ConnectionStates.DISCONNECTING
         self.config['state_change_callback'](self)
+        self._update_reconnect_backoff()
         if self._sock:
             self._sock.close()
             self._sock = None