baseplate.queue_consumer

Create a long-running process to consume from a queue. For example:

from kombu import Connection, Exchange
from baseplate import queue_consumer

def process_links(context, msg_body, msg):
    print('processing %s' % msg_body)

queue_consumer.consume(
    baseplate=make_baseplate(cfg, app_config),
    exchange=Exchange('reddit_exchange', 'direct'),
    connection=Connection(
      hostname='amqp://guest:guest@reddit.local:5672',
      virtual_host='/',
    ),
    queue_name='process_links_q',
    routing_keys=[
        'link_created',
        'link_deleted',
        'link_updated',
    ],
    handler=process_links,
)

This will create a queue named 'process_links_q' and bind the routing keys 'link_created', 'link_deleted', and 'link_updated'. It will then register a consumer for 'process_links_q' to read messages and feed them to process_links.

Register and run a queue consumer

baseplate.queue_consumer.consume(baseplate, exchange, connection, queue_name, routing_keys, handler)

Create a long-running process to consume messages from a queue.

A queue with name queue_name is created and bound to the routing_keys so messages published to the routing_keys are routed to the queue.

Next, the process registers a consumer that receives messages from the queue and feeds them to the handler.

The handler function must take 3 arguments:

• context: a baseplate context
• message_body: the text body of the message
• message: kombu.message.Message

The consumer will automatically ack each message after the handler method exits. If there is an error in processing and the message must be retried the handler should raise an exception to crash the process. This will prevent the ack and the message will be re-queued at the head of the queue.

Parameters:

• baseplate (baseplate.core.Baseplate) – A baseplate instance for the service.
• exchange (kombu.Exchange) –
• connection (kombu.connection.Connection) –
• queue_name (str) – The name of the queue.
• routing_keys (list) – List of routing keys.
• handler – The handler method.

class baseplate.queue_consumer.KombuConsumer(worker, worker_thread)

Consumer for use in baseplate.

The get_message() and get_batch() methods will automatically record diagnostic information.

get_message(server_span)

Return a single message.

Parameters:server_span (baseplate.core.ServerSpan) –

get_batch(server_span, max_items, timeout)

Return a batch of messages.

Parameters:

• server_span (baseplate.core.ServerSpan) –
• max_items (int) – The maximum batch size.
• timeout (int) – The maximum time to wait in seconds, or None for no timeout.

If you require more direct control

class baseplate.queue_consumer.BaseKombuConsumer(worker, worker_thread)

Base object for consuming messages from a queue.

A worker process accepts messages from the queue and puts them in a local work queue. The “real” consumer can then get messages with get_message() or get_batch(). It is that consumer’s responsibility to ack or reject messages.

Can be used directly, outside of standard baseplate context.

classmethod new(connection, queues)

Create and initialize a consumer.

Parameters:

• exchange (kombu.Exchange) –
• queues (list) – List of kombu.queue.Queue objects.

get_message()

Return a single message.

get_batch(max_items, timeout)

Return a batch of messages.

Parameters:

• max_items (int) – The maximum batch size.
• timeout (int) – The maximum time to wait in seconds, or None for no timeout.