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Hi Ask,

On Wed, Jul 25, 2012 at 1:01 PM, Ask Solem <ask at celeryproject.org> wrote:
> Dear list,
>
> I believe this is of interest to the Openstack people.
>
> I've just started maintaining a fork of the amqplib library,
> that differs by using AMQP 0.9.1 instead of 0.8, and that it supports
> heartbeats and the RabbitMQ extensions (consumer cancel notifications,
> publisher confirms and more).
>
> Heartbeats are used to detect if a connection has been closed (on either end),
> and is sometimes required in environments where network intermediates
> complicates connection loss detection (like certain firewalls).
>
> Consumer cancel notifications are important for HA, as it's the only
> way RabbitMQ can tell consumers that the queue it's consuming from went away.
>
> As you may or may not know, the amqp:// transport in Kombu now
> uses two different underlying libraries:
>
>  1) librabbitmq if installed
>
>       Python extension written in C (using the rabbitmq-c library)
>       http://github.com/celery/librabbitmq
>
>  2) amqplib as a fallback.
>
> The new client (http://pypi.python.org/pypi/amqp) will be the default fallback
> in 3.0 after librabbitmq has also been updated to support the new features.
>
> So for now if you requires these features you have to manually switch to the
> new client, luckily that's as easy as installing kombu 2.3 or later,
> + the 'amqp' library:
>
>  $ pip install kombu>=2.3 amqp
>
> then setting the broker URL to use 'pyamqp://' (or setting the broker transport
> to be 'pyamqp'):
>
>  from kombu import Connection
>  conn = Connection('pyamqp://guest:guest@localhost://')
>
> There's more information in the Kombu 2.3 changelog:
> http://kombu.readthedocs.org/en/latest/changelog.html
>
>
> NOTE TO IMPLEMENTORS:
>
> - Consumer cancel notifications
>
> Requires no changes to your code,
> all you need is to properly reconnect when one of the
> errors in Connection.channel_errors occur, which is handled
> automatically by Connection.ensure / Connection.autoretry (I don't believe
> Nova uses that, but it probably should).

Can you elaborate here? I'm working on RabbitMQ H/A support for nova
patch (almost done - just got some unexpected difficulties with
testing it) but even though I didn't explicitly account for this; but
we also didn't encounter any errors related to this in production.

Perhaps could you describe a way to test this?

Are these cancel notifications supported in any way (testable?) by the
Kombu memory transport?

>
> - Heartbeats
>
> For heartbeats to be used you need to periodically call the
> Connection.heartbeat_check method at regular intervals (
> suggested is twice the rate of the configured heartbeat).
>
> This shouldn't be any problem for Nova since it's using
> Eventlet. Special care must be taken so that the heartbeat value
> is not specified so low that blocking calls can defer heartbeats
> being sent out.
>
> An example of enabling heartbeats with eventlet could be:
>
> import weakref
> from kombu import Connection
> from eventlet import spawn_after
>
> def monitor_heartbeats(connection, rate=2):
> if not connection.heartbeat:
>     return
> interval = connection.heartbeat / 2.0
> cref = weakref.ref(connection)
>
> def heartbeat_check():
>     conn = cref()
>     if conn is not None and conn.connected:
>         conn.heartbeat_check(rate=rate)
>         spawn_after(interval, heartbeat_check)
>
>  return spawn_after(interval, heartbeat_check)
>
> connection = Connection('pyamq://', heartbeat=10)
>
> or:
>
> connection = Connection('pyamqp://?heartbeat=10')
>
>
> If you have any questions about implementing this,
> or about Kombu in general then please don't hesitate to contact
> me on this list, on twitter @asksol, or on IRC (also asksol)
>
>
> Regards,
>
> --
> Ask Solem
> twitter.com/asksol | +44 (0)7713357179
>
>
>
> --
> Ask Solem
> twitter.com/asksol | +44 (0)7713357179
>
>
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-- 
Eugene Kirpichov
http://www.linkedin.com/in/eugenekirpichov