Open Stack

On Mon, Dec 09, 2013 at 08:07:12PM +0900,
Isaku Yamahata <isaku.yamahata at gmail.com> wrote:

> On Mon, Dec 09, 2013 at 08:43:59AM +1300,
> Robert Collins <robertc at robertcollins.net> wrote:
> 
> > On 9 December 2013 01:43, Maru Newby <marun at redhat.com> wrote:
> > >
> > 
> > >>> If AMQP service is set up not to lose notification, notifications will be piled up
> > >>> and stress AMQP service. I would say single node failure isn't catastrophic.
> > >>
> > >> So we should have AMQP set to discard notifications if there is noone
> > >
> > > What are the semantics of AMQP discarding notifications when a consumer is no longer present?  Can this be relied upon to ensure that potentially stale notifications do not remain in the queue when an agent restarts?
> > 
> > If the queue is set to autodelete, it will delete when the agent
> > disconnects. There will be no queue until the agent reconnects. I
> > don't know if we expose that functionality via oslo.messaging, but
> > it's certainly something AMQP can do.
> 
> What happens if intermittent network instability occur?
> When the connection between agent <-> AMQP is unintentionally closed,
> will agent die or reconnect to it?

Answering myself. If connection is closed, it will reconnects automatically
at rpc layer. See neutron.openstack.common.rpc.impl_{kombu, qpid}.py.
So notifications during reconnects can be lost if AMQP service is set
to discard notifications during no subscriber.
-- 
Isaku Yamahata <isaku.yamahata at gmail.com>