import os
import random
import weakref
from redis.client import StrictRedis
from redis.connection import ConnectionPool, Connection
from redis.exceptions import ConnectionError, ResponseError, ReadOnlyError
from redis._compat import iteritems, nativestr, xrange
class MasterNotFoundError(ConnectionError):
pass
class SlaveNotFoundError(ConnectionError):
pass
class SentinelManagedConnection(Connection):
def __init__(self, **kwargs):
self.connection_pool = kwargs.pop('connection_pool')
super(SentinelManagedConnection, self).__init__(**kwargs)
def __repr__(self):
pool = self.connection_pool
s = '%s<service=%s%%s>' % (type(self).__name__, pool.service_name)
if self.host:
host_info = ',host=%s,port=%s' % (self.host, self.port)
s = s % host_info
return s
def connect_to(self, address):
self.host, self.port = address
super(SentinelManagedConnection, self).connect()
if self.connection_pool.check_connection:
self.send_command('PING')
if nativestr(self.read_response()) != 'PONG':
raise ConnectionError('PING failed')
def connect(self):
if self._sock:
return # already connected
if self.connection_pool.is_master:
self.connect_to(self.connection_pool.get_master_address())
else:
for slave in self.connection_pool.rotate_slaves():
try:
return self.connect_to(slave)
except ConnectionError:
continue
raise SlaveNotFoundError # Never be here
def read_response(self):
try:
return super(SentinelManagedConnection, self).read_response()
except ReadOnlyError:
if self.connection_pool.is_master:
# When talking to a master, a ReadOnlyError when likely
# indicates that the previous master that we're still connected
# to has been demoted to a slave and there's a new master.
# calling disconnect will force the connection to re-query
# sentinel during the next connect() attempt.
self.disconnect()
raise ConnectionError('The previous master is now a slave')
raise
class SentinelConnectionPool(ConnectionPool):
"""
Sentinel backed connection pool.
If ``check_connection`` flag is set to True, SentinelManagedConnection
sends a PING command right after establishing the connection.
"""
def __init__(self, service_name, sentinel_manager, **kwargs):
kwargs['connection_class'] = kwargs.get(
'connection_class', SentinelManagedConnection)
self.is_master = kwargs.pop('is_master', True)
self.check_connection = kwargs.pop('check_connection', False)
super(SentinelConnectionPool, self).__init__(**kwargs)
self.connection_kwargs['connection_pool'] = weakref.proxy(self)
self.service_name = service_name
self.sentinel_manager = sentinel_manager
def __repr__(self):
return "%s<service=%s(%s)" % (
type(self).__name__,
self.service_name,
self.is_master and 'master' or 'slave',
)
def reset(self):
super(SentinelConnectionPool, self).reset()
self.master_address = None
self.slave_rr_counter = None
def get_master_address(self):
master_address = self.sentinel_manager.discover_master(
self.service_name)
if self.is_master:
if self.master_address is None:
self.master_address = master_address
elif master_address != self.master_address:
# Master address changed, disconnect all clients in this pool
self.disconnect()
return master_address
def rotate_slaves(self):
"Round-robin slave balancer"
slaves = self.sentinel_manager.discover_slaves(self.service_name)
if slaves:
if self.slave_rr_counter is None:
self.slave_rr_counter = random.randint(0, len(slaves) - 1)
for _ in xrange(len(slaves)):
self.slave_rr_counter = (
self.slave_rr_counter + 1) % len(slaves)
slave = slaves[self.slave_rr_counter]
yield slave
# Fallback to the master connection
try:
yield self.get_master_address()
except MasterNotFoundError:
pass
raise SlaveNotFoundError('No slave found for %r' % (self.service_name))
def _checkpid(self):
if self.pid != os.getpid():
self.disconnect()
self.reset()
self.__init__(self.service_name, self.sentinel_manager,
is_master=self.is_master,
check_connection=self.check_connection,
connection_class=self.connection_class,
max_connections=self.max_connections,
**self.connection_kwargs)
class Sentinel(object):
"""
Redis Sentinel cluster client
>>> from redis.sentinel import Sentinel
>>> sentinel = Sentinel([('localhost', 26379)], socket_timeout=0.1)
>>> master = sentinel.master_for('mymaster', socket_timeout=0.1)
>>> master.set('foo', 'bar')
>>> slave = sentinel.slave_for('mymaster', socket_timeout=0.1)
>>> slave.get('foo')
'bar'
``sentinels`` is a list of sentinel nodes. Each node is represented by
a pair (hostname, port).
``min_other_sentinels`` defined a minimum number of peers for a sentinel.
When querying a sentinel, if it doesn't meet this threshold, responses
from that sentinel won't be considered valid.
``sentinel_kwargs`` is a dictionary of connection arguments used when
connecting to sentinel instances. Any argument that can be passed to
a normal Redis connection can be specified here. If ``sentinel_kwargs`` is
not specified, any socket_timeout and socket_keepalive options specified
in ``connection_kwargs`` will be used.
``connection_kwargs`` are keyword arguments that will be used when
establishing a connection to a Redis server.
"""
def __init__(self, sentinels, min_other_sentinels=0, sentinel_kwargs=None,
**connection_kwargs):
# if sentinel_kwargs isn't defined, use the socket_* options from
# connection_kwargs
if sentinel_kwargs is None:
sentinel_kwargs = dict([(k, v)
for k, v in iteritems(connection_kwargs)
if k.startswith('socket_')
])
self.sentinel_kwargs = sentinel_kwargs
self.sentinels = [StrictRedis(hostname, port, **self.sentinel_kwargs)
for hostname, port in sentinels]
self.min_other_sentinels = min_other_sentinels
self.connection_kwargs = connection_kwargs
def __repr__(self):
sentinel_addresses = []
for sentinel in self.sentinels:
sentinel_addresses.append('%s:%s' % (
sentinel.connection_pool.connection_kwargs['host'],
sentinel.connection_pool.connection_kwargs['port'],
))
return '%s<sentinels=[%s]>' % (
type(self).__name__,
','.join(sentinel_addresses))
def check_master_state(self, state, service_name):
if not state['is_master'] or state['is_sdown'] or state['is_odown']:
return False
# Check if our sentinel doesn't see other nodes
if state['num-other-sentinels'] < self.min_other_sentinels:
return False
return True
def discover_master(self, service_name):
"""
Asks sentinel servers for the Redis master's address corresponding
to the service labeled ``service_name``.
Returns a pair (address, port) or raises MasterNotFoundError if no
master is found.
"""
for sentinel_no, sentinel in enumerate(self.sentinels):
try:
masters = sentinel.sentinel_masters()
except ConnectionError:
continue
state = masters.get(service_name)
if state and self.check_master_state(state, service_name):
# Put this sentinel at the top of the list
self.sentinels[0], self.sentinels[sentinel_no] = (
sentinel, self.sentinels[0])
return state['ip'], state['port']
raise MasterNotFoundError("No master found for %r" % (service_name,))
def filter_slaves(self, slaves):
"Remove slaves that are in an ODOWN or SDOWN state"
slaves_alive = []
for slave in slaves:
if slave['is_odown'] or slave['is_sdown']:
continue
slaves_alive.append((slave['ip'], slave['port']))
return slaves_alive
def discover_slaves(self, service_name):
"Returns a list of alive slaves for service ``service_name``"
for sentinel in self.sentinels:
try:
slaves = sentinel.sentinel_slaves(service_name)
except (ConnectionError, ResponseError):
continue
slaves = self.filter_slaves(slaves)
if slaves:
return slaves
return []
def master_for(self, service_name, redis_class=StrictRedis,
connection_pool_class=SentinelConnectionPool, **kwargs):
"""
Returns a redis client instance for the ``service_name`` master.
A SentinelConnectionPool class is used to retrive the master's
address before establishing a new connection.
NOTE: If the master's address has changed, any cached connections to
the old master are closed.
By default clients will be a redis.StrictRedis instance. Specify a
different class to the ``redis_class`` argument if you desire
something different.
The ``connection_pool_class`` specifies the connection pool to use.
The SentinelConnectionPool will be used by default.
All other keyword arguments are merged with any connection_kwargs
passed to this class and passed to the connection pool as keyword
arguments to be used to initialize Redis connections.
"""
kwargs['is_master'] = True
connection_kwargs = dict(self.connection_kwargs)
connection_kwargs.update(kwargs)
return redis_class(connection_pool=connection_pool_class(
service_name, self, **connection_kwargs))
def slave_for(self, service_name, redis_class=StrictRedis,
connection_pool_class=SentinelConnectionPool, **kwargs):
"""
Returns redis client instance for the ``service_name`` slave(s).
A SentinelConnectionPool class is used to retrive the slave's
address before establishing a new connection.
By default clients will be a redis.StrictRedis instance. Specify a
different class to the ``redis_class`` argument if you desire
something different.
The ``connection_pool_class`` specifies the connection pool to use.
The SentinelConnectionPool will be used by default.
All other keyword arguments are merged with any connection_kwargs
passed to this class and passed to the connection pool as keyword
arguments to be used to initialize Redis connections.
"""
kwargs['is_master'] = False
connection_kwargs = dict(self.connection_kwargs)
connection_kwargs.update(kwargs)
return redis_class(connection_pool=connection_pool_class(
service_name, self, **connection_kwargs))
