[zeromq-dev] multiplexer pattern

Jakub Witkowski jpw at jabster.pl
Sun Sep 18 18:24:07 CEST 2011


Hello all,

Pardon me for intruding, but does this mean that ROUTER (and possibly
DEALER) sockets will now expose events like "peer disconnected"?
Because I can't imagine keeping the name - id table consistent without
it!

Thanks,

Jakub Witkowski


2011/9/18 Martin Sustrik <sustrik at 250bpm.com>:
> Hi Benjamin,
>
> The request/reply is moving to what it really is: A way for clients to
> access a set of homogenous and stateless services, providing a way to
> load-balance and handle failure in distributed systems.
>
> If you need multiple types of services, each provided by a different set
> of workers, you should create multiple topologies.
>
> Now, there are many use cases that don't fit into request/reply pattern
> -- in most cases these involve statefull workers. For such use cases
> there's the generic ROUTER socket in 4.0.
>
> The idea is that ROUTER socket allows you to do basically anything (send
> messages in any order, to any peer, you get notification about connects
> and disconnects etc.) and thus can be used to create new messaging
> patterns on top of 0MQ.
>
> If it turns out that the pattern is generally useful and well-defined it
> can then be merged into 0MQ itself. To create such a well-defined
> pattern you should think about how the pattern behaves in the face of
> overload (block? drop messages? retry?), how it deals with rogue clients
> (how to handle DoS attacks?), how it scales (can we add more
> intermediary nodes to the topology without breaking the semantics?) etc.
>
>> It would seem that this extremely basic pattern in 2.1 has become quite
>> complicated after the removal of identities.  I imagine that I will just
>> have to reimplement identity-routing myself on top of the new ROUTER
>> socket, with a lookup table in the MUX matching the engine-specified
>> identities to the real routing prefixes, and add extra handshaking to
>> the connection process to get this information everywhere it needs to be.
>
> Yes. It's going to be somewhat more painful, but AFAICS it boils down to:
>
> 1. Send a identity message manually after the connect.
> 2. On the server side, store the identity & connection ID in a map.
> 3. When request arrives at the server, check the map and forward the
> message to the right connection.
>
> Martin
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