[Openstack] Messaging reliability/durability expectations

Aaron Knister aaron.knister at gmail.com
Tue Oct 14 18:36:54 UTC 2014

Thanks Gordon, and Sandy.

With RabbitMQ if a message is silently dropped by the broker will a timeout
still occur/exception be raised because no reply/ack was received?

With the QPID driver the automatic ack()'s Sandy mentioned don't occur?
Will the sender eventually become aware that a message was lost? I'll take
a timeout over a silent message drop any day.



On Tue, Oct 14, 2014 at 1:33 PM, Gordon Sim <gsim at redhat.com> wrote:

> I agree that greater clarity on expectations around reliability are needed.
> The drivers all differ in this regard.
> As it stands today, the impl_rabbit driver only retries an RPC request if
> an exception occurs while sending it. However messages are sent
> unconfirmed[1]. This means a message can be lost before it gets enqueued by
> the broker, without the sender of the message receiving any error or
> notification of that fact.
> Even if the requests are durably stored and/or replicated in a clustered
> RabbitMQ configuration, the reply queues are currently always auto-deleted
> and are not durable regardless of configuration, so replies may be lost on
> broker failure even if requests are not.
> So I believe that various failures may cause an RPC request to fail (i.e.
> to timeout). It seems this is not universally expected however, so I am not
> sure how many OpenStack services using oslo.messaging expect and handle
> such failures.
> --Gordon
> [1] The impl_qpid driver by contrast sends messages synchronously - i.e.
> blocking until confirmed, but on the receive side it does not use
> acknowledgements so again message loss is possible.
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