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#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# © Copyright 2022, Scott Gasch
"""This is a module for making it easier to deal with Zookeeper / Kazoo."""
import datetime
import functools
import logging
import platform
import threading
import time
from typing import Callable, Optional
from kazoo.client import KazooClient
from kazoo.protocol.states import KazooState
import config
import file_utils
import scott_secrets
logger = logging.getLogger(__name__)
def obtain_lease(
f: Optional[Callable] = None,
*,
lease_id: str = config.PROGRAM_NAME,
contender_id: str = platform.node(),
initial_duration: datetime.timedelta = datetime.timedelta(minutes=5),
also_pass_lease: bool = False,
also_pass_zk_client: bool = False,
):
"""Obtain the named lease before invoking a function and skip
invoking the function if the lease cannot be obtained.
>>> @obtain_lease(lease_id='zookeeper_doctest')
... def f(name: str) -> int:
... print(f'Hello, {name}')
... return 123
>>> f('Scott')
Hello, Scott
123
"""
if not lease_id.startswith('/leases/'):
lease_id = f'/leases/{lease_id}'
lease_id = file_utils.fix_multiple_slashes(lease_id)
zk = KazooClient(
hosts=scott_secrets.ZOOKEEPER_NODES,
use_ssl=True,
verify_certs=False,
keyfile=scott_secrets.ZOOKEEPER_CLIENT_CERT,
keyfile_password=scott_secrets.ZOOKEEPER_CLIENT_PASS,
certfile=scott_secrets.ZOOKEEPER_CLIENT_CERT,
)
zk.start()
logger.debug('We have an active zookeeper connection.')
def wrapper(func: Callable) -> Callable:
@functools.wraps(func)
def wrapper2(*args, **kwargs):
logger.debug(
'Trying to obtain %s for contender %s now...',
lease_id,
contender_id,
)
lease = zk.NonBlockingLease(
lease_id,
initial_duration,
contender_id,
)
if lease:
logger.debug(
'Successfully obtained %s for contender %s; invoking user function.',
lease_id,
contender_id,
)
if also_pass_zk_client:
args = (*args, zk)
if also_pass_lease:
args = (*args, lease)
ret = func(*args, *kwargs)
else:
logger.debug(
'Failed to obtain %s for contender %s, doing nothing more.',
lease_id,
contender_id,
)
ret = None
logger.debug('Shutting down zookeeper client.')
zk.stop()
return ret
return wrapper2
if f is None:
return wrapper
else:
return wrapper(f)
def run_for_election(
f: Optional[Callable] = None,
*,
election_id: str = config.PROGRAM_NAME,
contender_id: str = platform.node(),
also_pass_zk_client: bool = False,
):
"""Run as a contender for a leader election. If/when we become
the leader, invoke the user's function.
The user's function will be executed on a new thread and must
accept a "stop processing" event that it must check regularly.
This event will be set automatically by the wrapper in the event
that we lose connection to zookeeper (and hence are no longer
confident that we are still the leader).
The user's function may return at any time which will cause
the wrapper to also return and effectively cede leadership.
Because the user's code is run in a separate thread, it may
not return anything.
>>> @run_for_election(
... election_id='zookeeper_doctest',
... also_pass_zk_client=True
... )
... def g(name: str, zk: KazooClient, stop_now: threading.Event):
... import time
... count = 0
... while True:
... print(f"Hello, {name}, I'm the leader.")
... if stop_now.is_set():
... print("Oops, not anymore?!")
... return
... time.sleep(0.1)
... count += 1
... if count >= 3:
... print("I'm sick of being leader.")
... return
>>> g("Scott")
Hello, Scott, I'm the leader.
Hello, Scott, I'm the leader.
Hello, Scott, I'm the leader.
I'm sick of being leader.
"""
if not election_id.startswith('/elections/'):
election_id = f'/elections/{election_id}'
election_id = file_utils.fix_multiple_slashes(election_id)
zk = KazooClient(
hosts=scott_secrets.ZOOKEEPER_NODES,
use_ssl=True,
verify_certs=False,
keyfile=scott_secrets.ZOOKEEPER_CLIENT_CERT,
keyfile_password=scott_secrets.ZOOKEEPER_CLIENT_PASS,
certfile=scott_secrets.ZOOKEEPER_CLIENT_CERT,
)
zk.start()
logger.debug('We have an active zookeeper connection.')
def wrapper(func: Callable) -> Callable:
@functools.wraps(func)
def runit(func, *args, **kwargs):
stop_event = threading.Event()
stop_event.clear()
if also_pass_zk_client:
args = (*args, zk)
args = (*args, stop_event)
logger.debug('Invoking user code on separate thread.')
thread = threading.Thread(
target=func,
args=args,
kwargs=kwargs,
)
thread.start()
while True:
state = zk.client_state
if state != KazooState.CONNECTED:
logger.error(
'Bad connection to zookeeper (state=%s); bailing out.',
state,
)
stop_event.set()
thread.join()
if not thread.is_alive():
logger.info('Child thread exited, I\'m exiting too.')
return
time.sleep(5.0)
@functools.wraps(runit)
def wrapper2(*args, **kwargs):
election = zk.Election(election_id, contender_id)
election.run(runit, func, *args, **kwargs)
zk.stop()
return wrapper2
if f is None:
return wrapper
else:
return wrapper(f)
if __name__ == '__main__':
import doctest
doctest.testmod()
|
