Pika 连接 rabbitmq 集群

原文：https://blog.csdn.net/Tech_Salon/article/details/82890431

使用 Pika 连接 rabbitmq 集群
使用 python 编程经常会用到 pika 来向 rabbitmq 发送消息，单个 rabbitmq 节点连接比较简单，本文介绍使用 rabbitmq 集群情况下的连接方式。

vip 连接方式
在 client 与 rabbitmq server 之间通过 haproxy 等负载均衡来提供 vip，我使用的环境就是采用这种方式，但是遇到某一节点挂掉时再访问 vip 连接 rabbitmq 集群会连接失败，常见 log 如下：

<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>
DEBUG:pika.adapters.select_connection:Using EPollPoller
DEBUG:pika.callback:Added: {'callback': <bound method SelectConnection._on_connection_start of <SelectConnection CLOSED socket=None params=<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>>>, 'only': None, 'one_shot': True, 'arguments': None, 'calls': 1}
DEBUG:pika.callback:Added: {'callback': <bound method SelectConnection._on_connection_close of <SelectConnection CLOSED socket=None params=<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>>>, 'only': None, 'one_shot': True, 'arguments': None, 'calls': 1}
DEBUG:pika.callback:Added: {'callback': <bound method _CallbackResult.set_value_once of <pika.adapters.blocking_connection._CallbackResult object at 0x7f869db987a0>>, 'only': None, 'one_shot': False, 'arguments': None}
DEBUG:pika.callback:Added: {'callback': <bound method _CallbackResult.set_value_once of <pika.adapters.blocking_connection._CallbackResult object at 0x7f869db98758>>, 'only': None, 'one_shot': False, 'arguments': None}
DEBUG:pika.callback:Added: {'callback': <bound method _CallbackResult.set_value_once of <pika.adapters.blocking_connection._CallbackResult object at 0x7f869db987e8>>, 'only': None, 'one_shot': False, 'arguments': None}
DEBUG:pika.adapters.select_connection:call_later: added timeout <pika.adapters.select_connection._Timeout object at 0x7f869dc0b6d0> with deadline=1538140088.706256 and callback=<bound method SelectConnection._on_connect_timer of <SelectConnection INIT socket=None params=<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>>>; now=1538140088.71; delay=0
INFO:pika.adapters.base_connection:Pika version 0.12.0 connecting to 10.10.11.1:5672
ERROR:pika.adapters.base_connection:Read empty data, calling disconnect
INFO:pika.connection:Disconnected from RabbitMQ at 10.10.11.1:5672 (-1): EOF
ERROR:pika.connection:Incompatible Protocol Versions
ERROR:pika.connection:Connection setup failed due to The protocol returned by the server is not supported: (-1, 'EOF')
DEBUG:pika.callback:Processing 0:_on_connection_error
DEBUG:pika.callback:Calling <bound method _CallbackResult.set_value_once of <pika.adapters.blocking_connection._CallbackResult object at 0x7f869db987a0>> for "0:_on_connection_error"
DEBUG:pika.callback:Processing 0:_on_connection_closed
DEBUG:pika.callback:Calling <bound method _CallbackResult.set_value_once of <pika.adapters.blocking_connection._CallbackResult object at 0x7f869db987e8>> for "0:_on_connection_closed"
DEBUG:pika.callback:Incremented callback reference counter: {'callback': <bound method SelectConnection._on_connection_start of <SelectConnection CLOSED socket=None params=<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>>>, 'only': None, 'one_shot': True, 'arguments': None, 'calls': 2}
DEBUG:pika.callback:Incremented callback reference counter: {'callback': <bound method SelectConnection._on_connection_close of <SelectConnection CLOSED socket=None params=<URLParameters host=10.10.11.1 port=5672 virtual_host=/ ssl=False>>>, 'only': None, 'one_shot': True, 'arguments': None, 'calls': 2}
ERROR:pika.adapters.blocking_connection:Connection open failed - The protocol returned by the server is not supported: (-1

这个报错通常是由于网络问题导致，尝试过 Telnet 连接 vip 和端口，都正常返回，目前还未找到 pika 访问 vip 连接 rabbitmq 失败的原因，所以采用类似于 openstack 中连接 rabbitmq 的方式，配置多主机列表，建立连接池。

配置 multiple hosts
openstack 配置transport_url 采用 rabbitmq 集群 host 列表方式，然后在 oslo.message 中建立连接池，通过 kombu 来使用 rabbitmq。参考这种方式，用 pika 实现。
pika 的官方文档中有示例参考 blocking_consume_recover_multiple_hosts

实际实现的时候会抛异常，原因是传递给 pika 需要是个实例而不是列表，官网上提供的方式把 host url 参数化后直接放到列表里传给 pika 进行连接：

node1 = pika.URLParameters('amqp://node1')
node2 = pika.URLParameters('amqp://node2')
node3 = pika.URLParameters('amqp://node3')
all_endpoints = [node1, node2, node3]
connection = pika.BlockingConnection(all_endpoints)

实际执行后报错如下：

Expected instance of Parameters, not [.........]

github 上提交的 issue： parameters error

目前不支持直接传入多 host url 来池化 rabbitmq 集群的连接，所以要在应用程序中单独实现。

用一个简单 for 循环来做：

random.shuffle(all_endpoints)
for url in all_endpoints:
    try:
        logging.basicConfig(level=logging.DEBUG)
        connection = pika.BlockingConnection(url)
    except Exception as ex:
        print str(ex)
    else:
        break

用 shuffle 来改变列表中的 host 顺序，可以起到负载均衡的作用。