This document describes the current stable version of Kombu (4.2). For development docs, go here.

Consumers

Basics

The Consumer takes a connection (or channel) and a list of queues to consume from. Several consumers can be mixed to consume from different channels, as they all bind to the same connection, and drain_events will drain events from all channels on that connection.

Note

Kombu since 3.0 will only accept json/binary or text messages by default, to allow deserialization of other formats you have to specify them in the accept argument (in addition to setting the right content type for your messages):

Consumer(conn, accept=['json', 'pickle', 'msgpack', 'yaml'])

Draining events from a single consumer:

with Consumer(connection, queues, accept=['json']):
    connection.drain_events(timeout=1)

Draining events from several consumers:

from kombu.utils.compat import nested

with connection.channel(), connection.channel() as (channel1, channel2):
    with nested(Consumer(channel1, queues1, accept=['json']),
                Consumer(channel2, queues2, accept=['json'])):
        connection.drain_events(timeout=1)

Or using ConsumerMixin:

from kombu.mixins import ConsumerMixin

class C(ConsumerMixin):

    def __init__(self, connection):
        self.connection = connection

    def get_consumers(self, Consumer, channel):
        return [
            Consumer(queues, callbacks=[self.on_message], accept=['json']),
        ]

    def on_message(self, body, message):
        print('RECEIVED MESSAGE: {0!r}'.format(body))
        message.ack()

C(connection).run()

and with multiple channels again:

from kombu import Consumer
from kombu.mixins import ConsumerMixin

class C(ConsumerMixin):
    channel2 = None

    def __init__(self, connection):
        self.connection = connection

    def get_consumers(self, _, default_channel):
        self.channel2 = default_channel.connection.channel()
        return [Consumer(default_channel, queues1,
                         callbacks=[self.on_message],
                         accept=['json']),
                Consumer(self.channel2, queues2,
                         callbacks=[self.on_special_message],
                         accept=['json'])]

    def on_consumer_end(self, connection, default_channel):
        if self.channel2:
            self.channel2.close()

C(connection).run()

There’s also a ConsumerProducerMixin for consumers that need to also publish messages on a separate connection (e.g. sending rpc replies, streaming results):

from kombu import Producer, Queue
from kombu.mixins import ConsumerProducerMixin

rpc_queue = Queue('rpc_queue')

class Worker(ConsumerProducerMixin):

    def __init__(self, connection):
        self.connection = connection

    def get_consumers(self, Consumer, channel):
        return [Consumer(
            queues=[rpc_queue],
            on_message=self.on_request,
            accept={'application/json'},
            prefetch_count=1,
        )]

    def on_request(self, message):
        n = message.payload['n']
        print(' [.] fib({0})'.format(n))
        result = fib(n)

        self.producer.publish(
            {'result': result},
            exchange='', routing_key=message.properties['reply_to'],
            correlation_id=message.properties['correlation_id'],
            serializer='json',
            retry=True,
        )
        message.ack()

See also

examples/rpc-tut6/ in the Github repository.

Advanced Topics

RabbitMQ

Consumer Priorities

RabbitMQ defines a consumer priority extension to the amqp protocol, that can be enabled by setting the x-priority argument to basic.consume.

In kombu you can specify this argument on the Queue, like this:

queue = Queue('name', Exchange('exchange_name', type='direct'),
              consumer_arguments={'x-priority': 10})

Read more about consumer priorities here: https://www.rabbitmq.com/consumer-priority.html

Reference