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：
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<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
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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：
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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)
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实际执行后报错如下：
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Expected instance of Parameters, not [.........]
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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：
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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
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用 shuffle 来改变列表中的 host 顺序，可以起到负载均衡的作用。