[nanomsg] Re: Persisted reliable messaging
- From: Martin Sustrik <sustrik@xxxxxxxxxx>
- To: nanomsg@xxxxxxxxxxxxx
- Date: Fri, 22 Nov 2013 11:18:22 +0100
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Hi Joerg,
> that nanomsg is a pure networking library is clear for me. I played
> around with it already. Alright. So let's say you have an internal
> message bus implemented via the Pub/Sub pattern (because you want
> to leverage the subscriptions). It is ok that the bus is in terms
> of crashes somehow atomic (either it works completely or not at
> all). Some of the subscribers are communicating with external
> systems and here you want to have more reliability (with
> persistence). if I get you right: your answer would be not to use
> nanomsg at all (at least for the communication to the external
> system), right?
It's really a matter of what you want to achieve. 100% reliability is
impossible.
If you want to be safe wrt. a box being destroyed (by fire or such)
you want to have mutliple outward facing boxes, presumably in
different buildings etc. IIRC RabbitMQ has clustered mode that could
help you with such setup, but still, you are not safe wrt. split-brain
syndrome etc.
If all you are interested in is being safe in the face of sender
process failing, RabbitMQ or a similar solution that writes data to
the disk, may solve your problem -- unless the process fails again
once it's restarted :)
Finally, if you want to be safe wrt network failures, TCP handles that
for you and you can use nanomsg as is.
That being said, you should be aware that with pub/sub there are only
2 mutually exclusive options: 1.) System will block/crash because of a
slow subscriber. 2.) Messages will be dropped when faced with a slow
consumer.
In other words, you either have a 24/7 support team that checks
whether the system is blocked and solves the problem when it occurs
(by killing consumers, adding more disk space or similar), or you
accept that messages will be lost sometimes.
Martin
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