Coordinate distributed systems.
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# -*- coding: utf-8 -*-
# Copyright (C) 2014 Yahoo! Inc. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License"); you may
# not use this file except in compliance with the License. You may obtain
# a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations
# under the License.
from distutils import version
import functools
import logging
import string
import threading
from oslo_utils import encodeutils
from oslo_utils import strutils
import redis
from redis import exceptions
from redis import sentinel
import tooz
from tooz import coordination
from tooz import locking
from tooz import utils
LOG = logging.getLogger(__name__)
def _handle_failures(func=None, n_tries=15):
"""Translates common redis exceptions into tooz exceptions.
This also enables retrying on certain exceptions.
:param func: the function to act on
:param n_tries: the number of retries
"""
if func is None:
return functools.partial(
_handle_failures,
n_tries=n_tries
)
@functools.wraps(func)
def wrapper(*args, **kwargs):
ntries = n_tries
while ntries > 1:
try:
return func(*args, **kwargs)
except exceptions.ConnectionError as e:
# retry ntries times and then raise a connection error
ntries -= 1
if ntries >= 1:
utils.raise_with_cause(coordination.ToozConnectionError,
encodeutils.exception_to_unicode(e),
cause=e)
except (exceptions.TimeoutError) as e:
utils.raise_with_cause(coordination.ToozConnectionError,
encodeutils.exception_to_unicode(e),
cause=e)
except exceptions.RedisError as e:
utils.raise_with_cause(tooz.ToozError,
encodeutils.exception_to_unicode(e),
cause=e)
return func(*args, **kwargs)
return wrapper
class RedisLock(locking.Lock):
def __init__(self, coord, client, name, timeout):
name = "%s_%s_lock" % (coord.namespace, str(name))
super(RedisLock, self).__init__(name)
# NOTE(jd) Make sure we don't release and heartbeat at the same time by
# using a exclusive access lock (LP#1557593)
self._exclusive_access = threading.Lock()
self._lock = client.lock(name,
timeout=timeout,
thread_local=False)
self._coord = coord
self._client = client
@_handle_failures
def is_still_owner(self):
lock_tok = self._lock.local.token
if not lock_tok:
return False
owner_tok = self._client.get(self.name)
return owner_tok == lock_tok
@_handle_failures
def break_(self):
return bool(self._client.delete(self.name))
@_handle_failures
def acquire(self, blocking=True, shared=False):
if shared:
raise tooz.NotImplemented
blocking, timeout = utils.convert_blocking(blocking)
acquired = self._lock.acquire(
blocking=blocking, blocking_timeout=timeout)
if acquired:
with self._exclusive_access:
self._coord._acquired_locks.add(self)
return acquired
@_handle_failures
def release(self):
with self._exclusive_access:
try:
self._lock.release()
except exceptions.LockError as e:
LOG.error("Unable to release lock '%r': %s", self, e)
return False
finally:
self._coord._acquired_locks.discard(self)
return True
@_handle_failures
def heartbeat(self):
with self._exclusive_access:
if self.acquired:
self._lock.reacquire()
return True
return False
@property
def acquired(self):
return self in self._coord._acquired_locks
class RedisDriver(coordination.CoordinationDriverCachedRunWatchers,
coordination.CoordinationDriverWithExecutor):
"""Redis provides a few nice benefits that act as a poormans zookeeper.
It **is** fully functional and implements all of the coordination
driver API(s). It stores data into `redis`_ using the provided `redis`_
API(s) using `msgpack`_ encoded values as needed.
- Durability (when setup with `AOF`_ mode).
- Consistent, note that this is still restricted to only
one redis server, without the recently released redis (alpha)
clustering > 1 server will not be consistent when partitions
or failures occur (even redis clustering docs state it is
not a fully AP or CP solution, which means even with it there
will still be *potential* inconsistencies).
- Master/slave failover (when setup with redis `sentinel`_), giving
some notion of HA (values *can* be lost when a failover transition
occurs).
The Redis driver connection URI should look like::
redis://[:PASSWORD@]HOST:PORT[?OPTION=VALUE[&OPTION2=VALUE2[&...]]]
For a list of options recognized by this driver, see the documentation
for the member CLIENT_ARGS, and to determine the expected types of those
options see CLIENT_BOOL_ARGS, CLIENT_INT_ARGS, and CLIENT_LIST_ARGS.
To use a `sentinel`_ the connection URI must point to the sentinel server.
At connection time the sentinel will be asked for the current IP and port
of the master and then connect there. The connection URI for sentinel
should be written as follows::
redis://<sentinel host>:<sentinel port>?sentinel=<master name>
Additional sentinel hosts are listed with multiple ``sentinel_fallback``
parameters as follows::
redis://<sentinel host>:<sentinel port>?sentinel=<master name>&
sentinel_fallback=<other sentinel host>:<sentinel port>&
sentinel_fallback=<other sentinel host>:<sentinel port>&
sentinel_fallback=<other sentinel host>:<sentinel port>
Further resources/links:
- http://redis.io/
- http://redis.io/topics/sentinel
- http://redis.io/topics/cluster-spec
Note that this client will itself retry on transaction failure (when they
keys being watched have changed underneath the current transaction).
Currently the number of attempts that are tried is infinite (this might
be addressed in https://github.com/andymccurdy/redis-py/issues/566 when
that gets worked on). See http://redis.io/topics/transactions for more
information on this topic.
General recommendations/usage considerations:
- When used for locks, run in AOF mode and think carefully about how
your redis deployment handles losing a server (the clustering support
is supposed to aid in losing servers, but it is also of unknown
reliablity and is relatively new, so use at your own risk).
.. _redis: http://redis.io/
.. _msgpack: http://msgpack.org/
.. _sentinel: http://redis.io/topics/sentinel
.. _AOF: http://redis.io/topics/persistence
"""
CHARACTERISTICS = (
coordination.Characteristics.DISTRIBUTED_ACROSS_THREADS,
coordination.Characteristics.DISTRIBUTED_ACROSS_PROCESSES,
coordination.Characteristics.DISTRIBUTED_ACROSS_HOSTS,
coordination.Characteristics.CAUSAL,
)
"""
Tuple of :py:class:`~tooz.coordination.Characteristics` introspectable
enum member(s) that can be used to interogate how this driver works.
"""
MIN_VERSION = version.LooseVersion("2.6.0")
"""
The min redis version that this driver requires to operate with...
"""
GROUP_EXISTS = b'__created__'
"""
Redis deletes dictionaries that have no keys in them, which means the
key will disappear which means we can't tell the difference between
a group not existing and a group being empty without this key being
saved...
"""
#: Value used (with group exists key) to keep a group from disappearing.
GROUP_EXISTS_VALUE = b'1'
#: Default namespace for keys when none is provided.
DEFAULT_NAMESPACE = b'_tooz'
NAMESPACE_SEP = b':'
"""
Separator that is used to combine a key with the namespace (to get
the **actual** key that will be used).
"""
DEFAULT_ENCODING = 'utf8'
"""
This is for python3.x; which will behave differently when returned
binary types or unicode types (redis uses binary internally it appears),
so to just stick with a common way of doing this, make all the things
binary (with this default encoding if one is not given and a unicode
string is provided).
"""
CLIENT_ARGS = frozenset([
'db',
'encoding',
'retry_on_timeout',
'socket_keepalive',
'socket_timeout',
'ssl',
'ssl_certfile',
'ssl_keyfile',
'sentinel',
'sentinel_fallback',
])
"""
Keys that we allow to proxy from the coordinator configuration into the
redis client (used to configure the redis client internals so that
it works as you expect/want it to).
See: http://redis-py.readthedocs.org/en/latest/#redis.Redis
See: https://github.com/andymccurdy/redis-py/blob/2.10.3/redis/client.py
"""
#: Client arguments that are expected/allowed to be lists.
CLIENT_LIST_ARGS = frozenset([
'sentinel_fallback',
])
#: Client arguments that are expected to be boolean convertible.
CLIENT_BOOL_ARGS = frozenset([
'retry_on_timeout',
'ssl',
])
#: Client arguments that are expected to be int convertible.
CLIENT_INT_ARGS = frozenset([
'db',
'socket_keepalive',
'socket_timeout',
])
#: Default socket timeout to use when none is provided.
CLIENT_DEFAULT_SOCKET_TO = 30
#: String used to keep a key/member alive (until it next expires).
STILL_ALIVE = b"Not dead!"
SCRIPTS = {
'create_group': """
-- Extract *all* the variables (so we can easily know what they are)...
local namespaced_group_key = KEYS[1]
local all_groups_key = KEYS[2]
local no_namespaced_group_key = ARGV[1]
if redis.call("exists", namespaced_group_key) == 1 then
return 0
end
redis.call("sadd", all_groups_key, no_namespaced_group_key)
redis.call("hset", namespaced_group_key,
"${group_existence_key}", "${group_existence_value}")
return 1
""",
'delete_group': """
-- Extract *all* the variables (so we can easily know what they are)...
local namespaced_group_key = KEYS[1]
local all_groups_key = KEYS[2]
local no_namespaced_group_key = ARGV[1]
if redis.call("exists", namespaced_group_key) == 0 then
return -1
end
if redis.call("sismember", all_groups_key, no_namespaced_group_key) == 0 then
return -2
end
if redis.call("hlen", namespaced_group_key) > 1 then
return -3
end
-- First remove from the set (then delete the group); if the set removal
-- fails, at least the group will still exist (and can be fixed manually)...
if redis.call("srem", all_groups_key, no_namespaced_group_key) == 0 then
return -4
end
redis.call("del", namespaced_group_key)
return 1
""",
'update_capabilities': """
-- Extract *all* the variables (so we can easily know what they are)...
local group_key = KEYS[1]
local member_id = ARGV[1]
local caps = ARGV[2]
if redis.call("exists", group_key) == 0 then
return -1
end
if redis.call("hexists", group_key, member_id) == 0 then
return -2
end
redis.call("hset", group_key, member_id, caps)
return 1
""",
}
"""`Lua`_ **template** scripts that will be used by various methods (they
are turned into real scripts and loaded on call into the :func:`.start`
method).
.. _Lua: http://www.lua.org
"""
EXCLUDE_OPTIONS = CLIENT_LIST_ARGS
def __init__(self, member_id, parsed_url, options):
super(RedisDriver, self).__init__(member_id, parsed_url, options)
self._parsed_url = parsed_url
self._encoding = self._options.get('encoding', self.DEFAULT_ENCODING)
timeout = self._options.get('timeout', self.CLIENT_DEFAULT_SOCKET_TO)
self.timeout = int(timeout)
self.membership_timeout = float(self._options.get(
'membership_timeout', timeout))
lock_timeout = self._options.get('lock_timeout', self.timeout)
self.lock_timeout = int(lock_timeout)
namespace = self._options.get('namespace', self.DEFAULT_NAMESPACE)
self._namespace = utils.to_binary(namespace, encoding=self._encoding)
self._group_prefix = self._namespace + b"_group"
self._beat_prefix = self._namespace + b"_beats"
self._groups = self._namespace + b"_groups"
self._client = None
self._acquired_locks = set()
self._started = False
self._server_info = {}
self._scripts = {}
def _check_fetch_redis_version(self, geq_version, not_existent=True):
if isinstance(geq_version, str):
desired_version = version.LooseVersion(geq_version)
elif isinstance(geq_version, version.LooseVersion):
desired_version = geq_version
else:
raise TypeError("Version check expects a string/version type")
try:
redis_version = version.LooseVersion(
self._server_info['redis_version'])
except KeyError:
return (not_existent, None)
else:
if redis_version < desired_version:
return (False, redis_version)
else:
return (True, redis_version)
@property
def namespace(self):
return self._namespace
@property
def running(self):
return self._started
def get_lock(self, name):
return RedisLock(self, self._client, name, self.lock_timeout)
_dumps = staticmethod(utils.dumps)
_loads = staticmethod(utils.loads)
@classmethod
def _make_client(cls, parsed_url, options, default_socket_timeout):
kwargs = {}
if parsed_url.hostname:
kwargs['host'] = parsed_url.hostname
if parsed_url.port:
kwargs['port'] = parsed_url.port
else:
if not parsed_url.path:
raise ValueError("Expected socket path in parsed urls path")
kwargs['unix_socket_path'] = parsed_url.path
if parsed_url.password:
kwargs['password'] = parsed_url.password
for a in cls.CLIENT_ARGS:
if a not in options:
continue
if a in cls.CLIENT_BOOL_ARGS:
v = strutils.bool_from_string(options[a])
elif a in cls.CLIENT_LIST_ARGS:
v = options[a]
elif a in cls.CLIENT_INT_ARGS:
v = int(options[a])
else:
v = options[a]
kwargs[a] = v
if 'socket_timeout' not in kwargs:
kwargs['socket_timeout'] = default_socket_timeout
# Ask the sentinel for the current master if there is a
# sentinel arg.
if 'sentinel' in kwargs:
sentinel_hosts = [
tuple(fallback.split(':'))
for fallback in kwargs.get('sentinel_fallback', [])
]
sentinel_hosts.insert(0, (kwargs['host'], kwargs['port']))
sentinel_server = sentinel.Sentinel(
sentinel_hosts,
socket_timeout=kwargs['socket_timeout'])
sentinel_name = kwargs['sentinel']
del kwargs['sentinel']
if 'sentinel_fallback' in kwargs:
del kwargs['sentinel_fallback']
master_client = sentinel_server.master_for(sentinel_name, **kwargs)
# The master_client is a redis.StrictRedis using a
# Sentinel managed connection pool.
return master_client
return redis.StrictRedis(**kwargs)
@_handle_failures
def _start(self):
super(RedisDriver, self)._start()
try:
self._client = self._make_client(self._parsed_url, self._options,
self.timeout)
except exceptions.RedisError as e:
utils.raise_with_cause(coordination.ToozConnectionError,
encodeutils.exception_to_unicode(e),
cause=e)
else:
# Ensure that the server is alive and not dead, this does not
# ensure the server will always be alive, but does insure that it
# at least is alive once...
self._server_info = self._client.info()
# Validate we have a good enough redis version we are connected
# to so that the basic set of features we support will actually
# work (instead of blowing up).
new_enough, redis_version = self._check_fetch_redis_version(
self.MIN_VERSION)
if not new_enough:
raise tooz.NotImplemented("Redis version greater than or"
" equal to '%s' is required"
" to use this driver; '%s' is"
" being used which is not new"
" enough" % (self.MIN_VERSION,
redis_version))
tpl_params = {
'group_existence_value': self.GROUP_EXISTS_VALUE,
'group_existence_key': self.GROUP_EXISTS,
}
# For py3.x ensure these are unicode since the string template
# replacement will expect unicode (and we don't want b'' as a
# prefix which will happen in py3.x if this is not done).
for (k, v) in tpl_params.copy().items():
if isinstance(v, bytes):
v = v.decode('ascii')
tpl_params[k] = v
prepared_scripts = {}
for name, raw_script_tpl in self.SCRIPTS.items():
script_tpl = string.Template(raw_script_tpl)
script = script_tpl.substitute(**tpl_params)
prepared_scripts[name] = self._client.register_script(script)
self._scripts = prepared_scripts
self.heartbeat()
self._started = True
def _encode_beat_id(self, member_id):
member_id = utils.to_binary(member_id, encoding=self._encoding)
return self.NAMESPACE_SEP.join([self._beat_prefix, member_id])
def _encode_member_id(self, member_id):
member_id = utils.to_binary(member_id, encoding=self._encoding)
if member_id == self.GROUP_EXISTS:
raise ValueError("Not allowed to use private keys as a member id")
return member_id
def _decode_member_id(self, member_id):
return utils.to_binary(member_id, encoding=self._encoding)
def _encode_group_leader(self, group_id):
group_id = utils.to_binary(group_id, encoding=self._encoding)
return b"leader_of_" + group_id
def _encode_group_id(self, group_id, apply_namespace=True):
group_id = utils.to_binary(group_id, encoding=self._encoding)
if not apply_namespace:
return group_id
return self.NAMESPACE_SEP.join([self._group_prefix, group_id])
def _decode_group_id(self, group_id):
return utils.to_binary(group_id, encoding=self._encoding)
@_handle_failures
def heartbeat(self):
beat_id = self._encode_beat_id(self._member_id)
expiry_ms = max(0, int(self.membership_timeout * 1000.0))
self._client.psetex(beat_id, time_ms=expiry_ms,
value=self.STILL_ALIVE)
for lock in self._acquired_locks.copy():
try:
lock.heartbeat()
except tooz.ToozError:
LOG.warning("Unable to heartbeat lock '%s'", lock,
exc_info=True)
return min(self.lock_timeout, self.membership_timeout)
@_handle_failures
def _stop(self):
while self._acquired_locks:
lock = self._acquired_locks.pop()
try:
lock.release()
except tooz.ToozError:
LOG.warning("Unable to release lock '%s'", lock, exc_info=True)
super(RedisDriver, self)._stop()
if self._client is not None:
# Make sure we no longer exist...
beat_id = self._encode_beat_id(self._member_id)
try:
# NOTE(harlowja): this will delete nothing if the key doesn't
# exist in the first place, which is fine/expected/desired...
self._client.delete(beat_id)
except tooz.ToozError:
LOG.warning("Unable to delete heartbeat key '%s'", beat_id,
exc_info=True)
self._client = None
self._server_info = {}
self._scripts.clear()
self._started = False
def _submit(self, cb, *args, **kwargs):
if not self._started:
raise tooz.ToozError("Redis driver has not been started")
return self._executor.submit(cb, *args, **kwargs)
def _get_script(self, script_key):
try:
return self._scripts[script_key]
except KeyError:
raise tooz.ToozError("Redis driver has not been started")
def create_group(self, group_id):
script = self._get_script('create_group')
def _create_group(script):
encoded_group = self._encode_group_id(group_id)
keys = [
encoded_group,
self._groups,
]
args = [
self._encode_group_id(group_id, apply_namespace=False),
]
result = script(keys=keys, args=args)
result = strutils.bool_from_string(result)
if not result:
raise coordination.GroupAlreadyExist(group_id)
return RedisFutureResult(self._submit(_create_group, script))
def update_capabilities(self, group_id, capabilities):
script = self._get_script('update_capabilities')
def _update_capabilities(script):
keys = [
self._encode_group_id(group_id),
]
args = [
self._encode_member_id(self._member_id),
self._dumps(capabilities),
]
result = int(script(keys=keys, args=args))
if result == -1:
raise coordination.GroupNotCreated(group_id)
if result == -2:
raise coordination.MemberNotJoined(group_id, self._member_id)
return RedisFutureResult(self._submit(_update_capabilities, script))
def leave_group(self, group_id):
encoded_group = self._encode_group_id(group_id)
encoded_member_id = self._encode_member_id(self._member_id)
def _leave_group(p):
if not p.exists(encoded_group):
raise coordination.GroupNotCreated(group_id)
p.multi()
p.hdel(encoded_group, encoded_member_id)
c = p.execute()[0]
if c == 0:
raise coordination.MemberNotJoined(group_id, self._member_id)
else:
self._joined_groups.discard(group_id)
return RedisFutureResult(self._submit(self._client.transaction,
_leave_group, encoded_group,
value_from_callable=True))
def get_members(self, group_id):
encoded_group = self._encode_group_id(group_id)
def _get_members(p):
if not p.exists(encoded_group):
raise coordination.GroupNotCreated(group_id)
potential_members = set()
for m in p.hkeys(encoded_group):
m = self._decode_member_id(m)
if m != self.GROUP_EXISTS:
potential_members.add(m)
if not potential_members:
return set()
# Ok now we need to see which members have passed away...
gone_members = set()
member_values = p.mget(map(self._encode_beat_id,
potential_members))
for (potential_member, value) in zip(potential_members,
member_values):
# Always preserve self (just incase we haven't heartbeated
# while this call/s was being made...), this does *not* prevent
# another client from removing this though...
if potential_member == self._member_id:
continue
if not value:
gone_members.add(potential_member)
# Trash all the members that no longer are with us... RIP...
if gone_members:
p.multi()
encoded_gone_members = list(self._encode_member_id(m)
for m in gone_members)
p.hdel(encoded_group, *encoded_gone_members)
p.execute()
return set(m for m in potential_members
if m not in gone_members)
return potential_members
return RedisFutureResult(self._submit(self._client.transaction,
_get_members, encoded_group,
value_from_callable=True))
def get_member_capabilities(self, group_id, member_id):
encoded_group = self._encode_group_id(group_id)
encoded_member_id = self._encode_member_id(member_id)
def _get_member_capabilities(p):
if not p.exists(encoded_group):
raise coordination.GroupNotCreated(group_id)
capabilities = p.hget(encoded_group, encoded_member_id)
if capabilities is None:
raise coordination.MemberNotJoined(group_id, member_id)
return self._loads(capabilities)
return RedisFutureResult(self._submit(self._client.transaction,
_get_member_capabilities,
encoded_group,
value_from_callable=True))
def join_group(self, group_id, capabilities=b""):
encoded_group = self._encode_group_id(group_id)
encoded_member_id = self._encode_member_id(self._member_id)
def _join_group(p):
if not p.exists(encoded_group):
raise coordination.GroupNotCreated(group_id)
p.multi()
p.hset(encoded_group, encoded_member_id,
self._dumps(capabilities))
c = p.execute()[0]
if c == 0:
# Field already exists...
raise coordination.MemberAlreadyExist(group_id,
self._member_id)
else:
self._joined_groups.add(group_id)
return RedisFutureResult(self._submit(self._client.transaction,
_join_group,
encoded_group,
value_from_callable=True))
def delete_group(self, group_id):
script = self._get_script('delete_group')
def _delete_group(script):
keys = [
self._encode_group_id(group_id),
self._groups,
]
args = [
self._encode_group_id(group_id, apply_namespace=False),
]
result = int(script(keys=keys, args=args))
if result in (-1, -2):
raise coordination.GroupNotCreated(group_id)
if result == -3:
raise coordination.GroupNotEmpty(group_id)
if result == -4:
raise tooz.ToozError("Unable to remove '%s' key"
" from set located at '%s'"
% (args[0], keys[-1]))
if result != 1:
raise tooz.ToozError("Internal error, unable"
" to complete group '%s' removal"
% (group_id))
return RedisFutureResult(self._submit(_delete_group, script))
def _destroy_group(self, group_id):
"""Should only be used in tests..."""
self._client.delete(self._encode_group_id(group_id))
def get_groups(self):
def _get_groups():
results = []
for g in self._client.smembers(self._groups):
results.append(self._decode_group_id(g))
return results
return RedisFutureResult(self._submit(_get_groups))
def _get_leader_lock(self, group_id):
name = self._encode_group_leader(group_id)
return self.get_lock(name)
def run_elect_coordinator(self):
for group_id, hooks in self._hooks_elected_leader.items():
leader_lock = self._get_leader_lock(group_id)
if leader_lock.acquire(blocking=False):
# We got the lock
hooks.run(coordination.LeaderElected(group_id,
self._member_id))
def run_watchers(self, timeout=None):
result = super(RedisDriver, self).run_watchers(timeout=timeout)
self.run_elect_coordinator()
return result
RedisFutureResult = functools.partial(coordination.CoordinatorResult)