Openstack之rabbitmq

rabbitmq 的工作流程和详细分析

1,rabbitmq 的 在openstack 项目中的调用过程分析

  • 在openstack 的项目中需要 oslo.messaging 插件包
  • oslo.messaging 的依赖包 kombu, pika.

在这里我们只分析 rabbitmq 相关的内容
OpenStack RPC 通信
Openstack 组件内部的 RPC(Remote Producer Call)机制的实现是基于 AMQP(Advanced Message Queuing Protocol)作为通讯模型,从而满足组件内部的松耦合性。AMQP 是用于异步消息通讯的消息中间件协议,AMQP 模型有四个重要的角色:

  • Exchange:根据 Routing key 转发消息到对应的 Message Queue 中
  • Routing key:用于 Exchange 判断哪些消息需要发送对应的 Message Queue
  • Publisher:消息发送者,将消息发送的 Exchange 并指明 Routing Key,以便 Message Queue 可以正确的收到消息
  • Consumer:消息接受者,从 Message Queue 获取消息

消息发布者 Publisher 将 Message 发送给 Exchange 并且说明 Routing Key。Exchange 负责根据 Message 的 Routing Key 进行路由,将 Message 正确地转发给相应的 Message Queue。监听在 Message Queue 上的 Consumer 将会从 Queue 中读取消息。
Routing Key 是 Exchange 转发信息的依据,因此每个消息都有一个 Routing Key 表明可以接受消息的目的地址,而每个 Message Queue 都可以通过将自己想要接收的 Routing Key 告诉 Exchange 进行 binding,这样 Exchange 就可以将消息正确地转发给相应的 Message Queue。图 2 就是 AMQP 消息模型。
图 2. AMQP 消息模型
AMQP

AMQP 定义了三种类型的 Exchange,不同类型 Exchange 实现不同的 routing 算法:

  • Direct Exchange:Point-to-Point 消息模式,消息点对点的通信模式,Direct Exchange 根据 Routing Key 进行精确匹配,只有对应的 Message Queue 会接受到消息
  • Topic Exchange:Publish-Subscribe(Pub-sub)消息模式,Topic Exchange 根据 Routing Key 进行模式匹配,只要符合模式匹配的 Message Queue 都会收到消息 (模糊匹配)
  • Fanout Exchange:广播消息模式,Fanout Exchange 将消息转发到所有绑定的 Message Queue

2, neutron 中所使用的 oslo.messaging 的服务分析

这个用dhcp-agent 服务为例子

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# neutron/cmd/eventlet/agents/dhcp.py

from neutron.agent import dhcp_agent

def main():
dhcp_agent.main()

# neutron/agent/dhcp_agent.py

from neutron.common import config as common_config

def main():
register_options(cfg.CONF)
common_config.init(sys.argv[1:])
config.setup_logging()
server = neutron_service.Service.create(
binary='neutron-dhcp-agent',
topic=topics.DHCP_AGENT,
report_interval=cfg.CONF.AGENT.report_interval,
manager='neutron.agent.dhcp.agent.DhcpAgentWithStateReport')
service.launch(cfg.CONF, server).wait()

# 这里分析 common_config.init(sys.argv[1:])
def init(args, **kwargs):
cfg.CONF(args=args, project='neutron',
version='%%(prog)s %s' % version.version_info.release_string(),
**kwargs)

# FIXME(ihrachys): if import is put in global, circular import
# failure occurs
from neutron.common import rpc as n_rpc
n_rpc.init(cfg.CONF)

# Validate that the base_mac is of the correct format
msg = attributes._validate_regex(cfg.CONF.base_mac,
attributes.MAC_PATTERN)
if msg:
msg = _("Base MAC: %s") % msg
raise Exception(msg)

# neutron/common/rpc.py
# 这里分析n_rpc.init
TRANSPORT_ALIASES = {
'neutron.openstack.common.rpc.impl_fake': 'fake',
'neutron.openstack.common.rpc.impl_qpid': 'qpid',
'neutron.openstack.common.rpc.impl_kombu': 'rabbit',
'neutron.openstack.common.rpc.impl_zmq': 'zmq',
'neutron.rpc.impl_fake': 'fake',
'neutron.rpc.impl_qpid': 'qpid',
'neutron.rpc.impl_kombu': 'rabbit',
'neutron.rpc.impl_zmq': 'zmq',
}

def init(conf):
global TRANSPORT, NOTIFIER
exmods = get_allowed_exmods()
TRANSPORT = oslo_messaging.get_transport(conf,
allowed_remote_exmods=exmods,
aliases=TRANSPORT_ALIASES)
serializer = RequestContextSerializer()
NOTIFIER = oslo_messaging.Notifier(TRANSPORT, serializer=serializer)

# 这里重点分析 oslo_messaging.get_transport() 方法
# oslo.messaging/transport.py 文件
#
def get_transport(conf, url=None, allowed_remote_exmods=None, aliases=None):
allowed_remote_exmods = allowed_remote_exmods or []
# 这里就涉及到 3 个 配置文件的选项
# transport_url = transport://user:pass@host1:port[,hostN:portN]/virtual_host
# rpc_backend = rabbitmq
# control_exchange = oepnstack

conf.register_opts(_transport_opts)

if not isinstance(url, TransportURL):
url = url or conf.transport_url
parsed = TransportURL.parse(conf, url, aliases)
if not parsed.transport:
raise InvalidTransportURL(url, 'No scheme specified in "%s"' % url)
url = parsed

kwargs = dict(default_exchange=conf.control_exchange,
allowed_remote_exmods=allowed_remote_exmods)

# url.transport.split('+')[0] = 'rabbit'
try:
mgr = driver.DriverManager('oslo.messaging.drivers',
url.transport.split('+')[0],
invoke_on_load=True,
invoke_args=[conf, url],
invoke_kwds=kwargs)
# 导入rabbitmq的namespace "oslo.messaging.drivers;" 的setup.cfg 相关的driver 类
# invoke_on_load=True 并且初始化
# 初始化的参数invoke_args=[conf, url], invoke_kwds=kwargs
#oslo.messaging.drivers =
# rabbit = oslo_messaging._drivers.impl_rabbit:RabbitDriver

except RuntimeError as ex:
raise DriverLoadFailure(url.transport, ex)

#初始化 Transport 类
return Transport(mgr.driver)
# 代码中的driver.DriverManager 为初始化 driver类
class RabbitDriver(amqpdriver.AMQPDriverBase):
"""RabbitMQ Driver

The ``rabbit`` driver is the default driver used in OpenStack's
integration tests.

The driver is aliased as ``kombu`` to support upgrading existing
installations with older settings.

"""

def __init__(self, conf, url,
default_exchange=None,
allowed_remote_exmods=None):
opt_group = cfg.OptGroup(name='oslo_messaging_rabbit',
title='RabbitMQ driver options')
conf.register_group(opt_group)
conf.register_opts(rabbit_opts, group=opt_group)
conf.register_opts(rpc_amqp.amqp_opts, group=opt_group)
conf.register_opts(base.base_opts, group=opt_group)

self.missing_destination_retry_timeout = (
conf.oslo_messaging_rabbit.kombu_missing_consumer_retry_timeout)

self.prefetch_size = (
conf.oslo_messaging_rabbit.rabbit_qos_prefetch_count)

connection_pool = pool.ConnectionPool(
conf, conf.oslo_messaging_rabbit.rpc_conn_pool_size,
url, Connection)

super(RabbitDriver, self).__init__(
conf, url,
connection_pool,
default_exchange,
allowed_remote_exmods
)


#这里我们分析 Transport 类的初始化
class Transport(object):

"""A messaging transport.

This is a mostly opaque handle for an underlying messaging transport
driver.

It has a single 'conf' property which is the cfg.ConfigOpts instance used
to construct the transport object.
"""

def __init__(self, driver):
self.conf = driver.conf
self._driver = driver

#到这里我们的rpc 相关的都初始化完成了

分析rpc 服务的代码流程

1, rpc 服务的 server 端 也就是 receive 端接受消息

  • rpc server 端就是一个 接受 消息端
  • rpc server 端需要一个 回调方法 collback 方法
  • rpc server 端是创建 consumer (消费者)

分析 oslo.messaging 包的分析 oslo_messaging/_drivers/./impl_rabbit.py

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# 创建一个 direct 队列
# 队列 routing_key = queue_name = topic
def declare_direct_consumer(self, topic, callback):
"""Create a 'direct' queue.
In nova's use, this is generally a msg_id queue used for
responses for call/multicall
"""

consumer = Consumer(exchange_name=topic,
queue_name=topic,
routing_key=topic,
type='direct',
durable=False,
exchange_auto_delete=True,
queue_auto_delete=False,
callback=callback,
rabbit_ha_queues=self.rabbit_ha_queues,
rabbit_queue_ttl=self.rabbit_transient_queues_ttl)

self.declare_consumer(consumer)

def declare_topic_consumer(self, exchange_name, topic, callback=None,
queue_name=None):
"""Create a 'topic' consumer."""
consumer = Consumer(exchange_name=exchange_name,
queue_name=queue_name or topic,
routing_key=topic,
type='topic',
durable=self.amqp_durable_queues,
exchange_auto_delete=self.amqp_auto_delete,
queue_auto_delete=self.amqp_auto_delete,
callback=callback,
rabbit_ha_queues=self.rabbit_ha_queues)

self.declare_consumer(consumer)

#创建一个 fanout 的 consumer
#第一步 需要 验证 exchange 是否存在
self.exchange = kombu.entity.Exchange(
name=exchange_name,
type=type,
durable=self.durable,
auto_delete=self.exchange_auto_delete)
# 第二步 创建 queue 指定 exchange 并且给定 routing_key
def declare(self, conn):
"""Re-declare the queue after a rabbit (re)connect."""
self.queue = kombu.entity.Queue(
name=self.queue_name,
channel=conn.channel,
exchange=self.exchange,
durable=self.durable,
auto_delete=self.queue_auto_delete,
routing_key=self.routing_key,
queue_arguments=self.queue_arguments)

try:
LOG.trace('ConsumerBase.declare: '
'queue %s', self.queue_name)
self.queue.declare()
except conn.connection.channel_errors as exc:
# NOTE(jrosenboom): This exception may be triggered by a race
# condition. Simply retrying will solve the error most of the time
# and should work well enough as a workaround until the race
# condition itself can be fixed.
# See https://bugs.launchpad.net/neutron/+bug/1318721 for details.
if exc.code == 404:
self.queue.declare()
else:
raise

#在创建 fanout 的消费者时候 不需要指定 routing_key
def declare_fanout_consumer(self, topic, callback):
"""Create a 'fanout' consumer."""

unique = uuid.uuid4().hex
exchange_name = '%s_fanout' % topic
queue_name = '%s_fanout_%s' % (topic, unique)

consumer = Consumer(exchange_name=exchange_name,
queue_name=queue_name,
routing_key=topic,
type='fanout',
durable=False,
exchange_auto_delete=True,
queue_auto_delete=False,
callback=callback,
rabbit_ha_queues=self.rabbit_ha_queues,
rabbit_queue_ttl=self.rabbit_transient_queues_ttl)

self.declare_consumer(consumer)

RPC 发送请求

Client 端发送 RPC 请求由 publisher 发送消息并声明消息地址,consumer 接收消息并进行消息处理,如果需要消息应答则返回处理请求的结果消息。OpenStack RPC 模块提供了 :

rpc.call,
rpc.cast,
rpc.fanout_cast,

三种 RPC 调用方法,发送和接收 RPC 请求。

rpc.call 发送 RPC 请求并返回请求处理结果,

请求处理流程如图 5 所示,
call
由 Topic Publisher 发送消息,
Topic Exchange 根据消息地址进行消息转发至对应的 Message Queue 中,
Topic Consumer 监听 Message Queue,发现需要处理的消息则进行消息处理,
并由 Direct Publisher 将请求处理结果消息,请求发送方创建 Direct Consumer 监听消息的返回结果

rpc.cast 发送 RPC 请求无返回,请求处理流程如图 6 所示,与 rpc.call 不同之处在于,不需要请求处理结果的返回,因此没有 Direct Publisher 和 Direct Consumer 处理。
cast

图 7. RPC.fanout 消息处理
fanout_cast

cast, call 代码分析

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# cast 没有返回结果
def cast(self, ctxt, method, **kwargs):
"""Invoke a method and return immediately. See RPCClient.cast()."""
msg = self._make_message(ctxt, method, kwargs)
ctxt = self.serializer.serialize_context(ctxt)

if self.version_cap:
self._check_version_cap(msg.get('version'))
try:
self.transport._send(self.target, ctxt, msg, retry=self.retry)
except driver_base.TransportDriverError as ex:
raise ClientSendError(self.target, ex)

# call 有返回结果
def call(self, ctxt, method, **kwargs):
"""Invoke a method and wait for a reply. See RPCClient.call()."""
if self.target.fanout:
raise exceptions.InvalidTarget('A call cannot be used with fanout',
self.target)

msg = self._make_message(ctxt, method, kwargs)
msg_ctxt = self.serializer.serialize_context(ctxt)

timeout = self.timeout
if self.timeout is None:
timeout = self.conf.rpc_response_timeout

if self.version_cap:
self._check_version_cap(msg.get('version'))

try:
result = self.transport._send(self.target, msg_ctxt, msg,
wait_for_reply=True, timeout=timeout,
retry=self.retry)
except driver_base.TransportDriverError as ex:
raise ClientSendError(self.target, ex)
return self.serializer.deserialize_entity(ctxt, result)