在Django中使用zerorpc
在Django中使用zerorpc
前言
随着系统架构从集中式单点服务器到分布式微服务方向的迁移,RPC是一个不可回避的话题.如何在系统中引入对开发者友好,性能可靠的RPC服务是一个值得深思的问题.
在调研了Thrift,gRPC,zerorpc等方案后,基于以下2点最后选择了zerorpc:
- Thrift,gRPC学习成本高,开发者需要重新定义返回结构增加了工作量
- zerorpc完美契合Python,能快速开发,并且支持Node.js,适用于当前技术栈
问题
虽然zerorpc可以直接嵌入当前系统框架中,但是还是有一些问题需要去考虑解决
-
rpc 接口如何定义
-
rpc 服务如何启动
-
高并发情况下客户端的可靠性
服务端
在当前的系统中大量使用Celery,djang-celery定义Task的方式是在每个install app中定义tasks.py文件,然后通过@task装饰器来生成Task.所以这里为了方便定义rpc interface设计一套类似于Celery的规范.需要输出rpc interface的app下面创建rpcs.py文件
# rpcs.py
# coding: utf-8
from eebo.core.utils.zrpc import rpc
from .models import Ticket
from .serializers import TicketSerializer
@rpc.register()
def get_ticket():
t = Ticket.objects.first()
s = TicketSerializer(t)
return s.data
@rpc.register(name='ticket_list', stream=True)
def get_tickets(n):
qs = Ticket.objects.all()[:n]
s = TicketSerializer(qs, many=True)
return iter(s.data)
rpc.register装饰器用来注册函数到rpc服务上,可选参数:
- name: 客户调用方法名称, 没有写的情况下就是func name如get_ticket
- stream: 默认False, 如果为True, 则使用zerorpc的流式响应传输, 数据量比较大的情况时使用, 返回可迭代对象
我们来看看eebo.core.utils.zrpc如何来实现这个注册过程:
# coding: utf-8
import zerorpc
class RPC(object):
@classmethod
def register(cls, name=None, stream=False):
def _wrapper(func):
setattr(cls, name or func.__name__, zerorpc.stream(
lambda self, *args, **kwargs: func(*args, **kwargs)) if stream
else staticmethod(func))
return func
return _wrapper
rpc = RPC()
通过一个类方法来往类上面绑定方法,需要注意的是name的定义必须是全局唯一的.
现在我们有了定义rpc interface的方法,下面来看看如何启动rpc server.
# runrpc.py
# coding: utf-8
import re
import sys
import imp as _imp
import importlib
from django.conf import settings
from django.core.management.base import BaseCommand, CommandError
from eebo.core.utils.zrpc import rpc, ServerExecMiddleware
naiveip_re = re.compile(r"""^(?:
(?P<addr>
(?P<ipv4>\d{1,3}(?:\.\d{1,3}){3}) | # IPv4 address
(?P<ipv6>\[[a-fA-F0-9:]+\]) | # IPv6 address
(?P<fqdn>[a-zA-Z0-9-]+(?:\.[a-zA-Z0-9-]+)*) # FQDN
):)?(?P<port>\d+)$""", re.X)
class Command(BaseCommand):
help = "Starts a lightweight RPC server for development."
default_addr = '127.0.0.1'
default_port = '4242'
def add_arguments(self, parser):
parser.add_argument('addrport',
nargs='?',
help='Optional port number, or ipaddr:port')
def handle(self, *args, **options):
self.use_ipv6 = False
if not options['addrport']:
self.addr = ''
self.port = self.default_port
else:
m = re.match(naiveip_re, options['addrport'])
if m is None:
raise CommandError('"%s" is not a valid port number '
'or address:port pair.' %
options['addrport'])
self.addr, _ipv4, _ipv6, _fqdn, self.port = m.groups()
if not self.port.isdigit():
raise CommandError("%r is not a valid port number." %
self.port)
if self.addr:
if _ipv6:
self.addr = self.addr[1:-1]
self.use_ipv6 = True
self._raw_ipv6 = True
elif self.use_ipv6 and not _fqdn:
raise CommandError('"%s" is not a valid IPv6 address.' %
self.addr)
if not self.addr:
self.addr = self.default_addr_ipv6 if self.use_ipv6 else self.default_addr
self._raw_ipv6 = self.use_ipv6
self.run(**options)
def run(self, **options):
"""Run the server, using the autoreloader if needed."""
self.autodiscover_rpc()
server = self.get_server()
try:
server.run()
except KeyboardInterrupt:
server.close()
sys.exit(0)
def autodiscover_rpc(self, related_name='rpcs'):
for pkg in settings.INSTALLED_APPS:
try:
pkg_path = importlib.import_module(pkg).__path__
except AttributeError:
continue
try:
_imp.find_module(related_name, pkg_path)
except ImportError:
continue
try:
importlib.import_module('{0}.{1}'.format(pkg, related_name))
except ImportError:
pass
def get_server(self, *args, **options):
"""Return the default zerorpc server for the runner."""
import zerorpc
server = zerorpc.Server(rpc, heartbeat=30)
server.bind("tcp://{0}:{1}".format(self.addr, self.port))
# close django old connections
zerorpc.Context.get_instance().register_middleware(ServerExecMiddleware())
# for sentry
try:
from raven.contrib.zerorpc import SentryMiddleware
if hasattr(settings, 'RAVEN_CONFIG'):
sentry = SentryMiddleware(hide_zerorpc_frames=False,
dsn=settings.RAVEN_CONFIG['dsn'])
zerorpc.Context.get_instance().register_middleware(sentry)
except ImportError:
pass
return server
runrpc.py是一个Django management commands 文件需要放到某个install app目录的management/commands下面,启动服务器:
python manage.py runrpc 0.0.0.0:4242autodiscover_rpc自动发现rpc interface注册函数get_server生成zerorpc server对象
在get_server中对zerorpc注册了2个中间件,SentryMiddleware用于捕获rpc interface抛出的异常发送到sentry,ServerExecMiddleware用于处理Django db connection,看看代码:
# zrpc.py
# coding: utf-8
from django.db import close_old_connections
class ServerExecMiddleware(object):
def server_before_exec(self, request_event):
close_old_connections()
def server_after_exec(self, request_event, reply_event):
close_old_connections()
在每个rpc interface被调用前与调用后都调用close_old_connections关闭db connection,这里是为了实现django.db中对请求处理前与处理后注册信号:
django.db.__init__.py signals.request_started.connect(close_old_connections) signals.request_finished.connect(close_old_connections)
目的是保证在rpc interface中使用ORM时,connection没有超时断开.
客户端
由于rpc的调用是阻塞的,不能全局只创建一个client.但是也不能每个请求都创建client,所以这里参考redis-py的client实现,定义一个支持连接池的zerorpc client.
# zrpc.py
# coding: utf-8
import os
import zerorpc
from redis.connection import BlockingConnectionPool
from gevent.queue import LifoQueue
class Connection(object):
def __init__(self, connect_to, heartbeat=30):
self.client = zerorpc.Client(heartbeat=heartbeat)
self.client.connect(connect_to)
self.pid = os.getpid()
def disconnect(self):
self.client.close()
class RPCClient(object):
def __init__(self, connect_to, heartbeat=30):
self.connection_pool = BlockingConnectionPool(connection_class=Connection,
queue_class=LifoQueue, timeout=heartbeat, connect_to=connect_to, heartbeat=heartbeat)
def close(self):
self.connection_pool.disconnect()
def __getattr__(self, name):
return lambda *args, **kwargs: self(name, *args, **kwargs)
def __call__(self, name, *args, **kwargs):
connection = self.connection_pool.get_connection('')
try:
return getattr(connection.client, name)(*args, **kwargs)
finally:
self.connection_pool.release(connection)
这里直接复用了redis-py定义的连接池,当前系统使用gunicorn + gevent的方式启动Django服务,所以queue_class使用了gevent的LifoQueue.
在使用过程中还发现了这个问题:
需要打个补丁解决:
import zmq.green as zmq # patch zmq garbage-collection Thread to use green Context: from zmq.utils.garbage import gc gc.context = zmq.Context()
总结
技术的选型需要契合项目实际情况,不要盲目上新技术引入不必要的成本.为了推广方案,必须全局的考虑方案是否易使用,是否易部署.
完整代码:
https://gist.github.com/zhu327/5b6c06eccc5758d4e642ee899a518687
