[zeromq-dev] What exact networking problems ZMQ does solve?

Justin Cook jhcook at gmail.com
Wed Dec 11 11:50:36 CET 2013


Artem,

There is no way to know that a node on the network went down without the lack of receiving acknowledgements that the message was received — either with TCP ACKs or a messaging pattern in 0MQ such as REQ/REP.  

If the the server is not up yet, and you have not established a session, then Bruno has given you the option to workaround that. If the server goes down, and their is an established session, there is no way to know that without further communication, or no response where response is expected.

If there is, I would love to know about it.  

--  
Justin Cook


On Wednesday, 11 December 2013 at 10:42, artemv zmq wrote:

> hi Justin. Thanks for heads up.
>  
> Ok. Clear. Especially about steady stream.  
>  
> But, again, let me make it very clear.  
> I imagine following situations and desired outcomes:
> - Server is not up yet, and client tries to send a message. Desired outcome: big red alarm -- "fail" w/o waiting for reply.
> - Server is up, client sends a message, gets reply, everything is smooth. Then the network between client and server is getting down (e.g. "ifdown eth0" on server). The client tries to send a message... Desired outcome: big red alarm -- "fail" w/o waiting for reply.  
>  
> I don't care server is up or down, or in what status an infrastructure is. I want to know one thing -- did all frames (of my message) been sent or not ?
>  
> Is it posible with ZMQ?  
>  
>  
> BR
> -artemv
>  
>  
>  
> 2013/12/11 Justin Cook <jhcook at gmail.com (mailto:jhcook at gmail.com)>
> > Artem,
> >  
> > This is a problem that every network developer faces. Did my message make it to its destination? If I send a message, is it likely to make it to the recipient?
> >  
> > Fortunately, there are patterns to use to increase reliability, but even then there is no way to be 100% sure that when a message is sent, it will flow across the infrastructure and be delivered with 100% certainty without an acknowledgement.
> >  
> > You cannot _instantly_ get an indication a server failed — or the associated infrastructure — unless you have a steady stream of bytes going across the wire, and they suddenly stop. If you want to know a node went down, you will need heartbeat messages. There are a few ways to do this.
> >  
> > Please look at the paranoid pirate example and this:
> >  
> > http://zguide.zeromq.org/page:all#Heartbeating
> >  
> > --
> > Justin Cook
> >  
> >  
> > On Wednesday, 11 December 2013 at 09:59, artemv zmq wrote:
> >  
> > > Okay. Thanks for your thoughts. Again, I read the guide, and I know on practice what's pub/sub/push/pull/ .. and so on.
> > >  
> > > But let me ask one more time very concrete and simple question. I want to develop a client/server appl. Okay. I pick dealer/router pattern. Fine. Now my requirement is following:
> > > if server is unaccessible (wrong ip address, server is not online, server was online and then went offline, etc.) -- in this case I want to get (_instantly_) some indication that client can't send a message because server is unaccessible. It's clear? Again, I don't want to await for reply, I want to know right now that I can't send a message.
> > >  
> > > Realistically, this is very classic networking issue :) So, how can ZMQ help me? Or is it possible/eligible et al to implement transactional (not batching!) applications on ZMQ?
> > >  
> > >  
> > > BR
> > > -artemv
> > >  
> > >  
> > >  
> > >  
> > >  
> > >  
> > > 2013/12/11 Bruno D. Rodrigues <bruno.rodrigues at litux.org (mailto:bruno.rodrigues at litux.org) (mailto:bruno.rodrigues at litux.org)>
> > > > zeromq.org (http://zeromq.org) (http://zeromq.org) - learn the basics - http://zeromq.org/intro:read-the-manual - the guide - http://zguide.zeromq.org/page:all
> > > >  
> > > > I just gave you a short description of how Ømq is solving the network problems for me.
> > > >  
> > > > On Dec 11, 2013, at 6:59, asif saeed <asif.lse2 at gmail.com (mailto:asif.lse2 at gmail.com) (mailto:asif.lse2 at gmail.com)> wrote:
> > > > > Hi Bruno,
> > > > >  
> > > > > On Wed, Dec 11, 2013 at 12:38 AM, Bruno D. Rodrigues <bruno.rodrigues at litux.org (mailto:bruno.rodrigues at litux.org) (mailto:bruno.rodrigues at litux.org)> wrote:
> > > > > > Xsub xpub for distribution load balancing
> > > > >  
> > > > >  
> > > > >  
> > > > > What is Xsub xpub? Could you please explain these terms or give me a link to an online resource where these terms are explained in detail?
> > > > >  
> > > > > Thanks in advance,
> > > > > -Asif
> > > > >  
> > > > >  
> > > > >  
> > > > >  
> > > > >  
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