[zeromq-dev] Router Example & questions

[Pieter Hintjens]

Hi Troy,

There's a pattern for fully decentralized clusters, in Chapter 8. To
ensure we don't lose messages randomly, we use dealer-router in a
symmetric way. Pure router-router is fragile in several ways, and I'd
not recommend it.

-Pieter

On Sun, Mar 9, 2014 at 8:20 PM, Troy Settle <troy.settle at gmail.com> wrote:
> I've been digging around 0MQ for a short time now, and one of the things
> that is not discussed heavily in the guide, is the ROUTER to ROUTER pair,
> which would be highly useful in a completely decentralized P2P network.  So,
> after working through some of the examples in the Guide, I came up with this
> code.  It's in PHP, and if nobody takes my fun away, I'll write it also in C
> and/or C++ (assuming I can get back up to speed in them).  Please feel free
> to use this in the 0MQ Guide (with or without cleanup).
>
> http://pastebin.com/zW548wpN
>
> I called it node.php.  There's probably a better name as a piece of example
> code.
>
> $ php node.php <port> <peers>
>
> It will fork out as many peers as you want (at least 2), each binding to
> <port>+n and connecting to each previous node that's already bound.  What
> you end up with, is any number of nodes, all connected (in some way) to all
> the other nodes.  If you launch a few nodes, all messages will be received.
> If you launch many nodes, messages will dropped, as the oldest and youngest
> nodes don't overlap quite enough.  You can play with the sleep on line 60 to
> have some fun.  Comment out the printf() and echo statements in the loop if
> you want to reduce the noise.  The zhelpers.php include isn't necessary, it
> was left over from a previous experiment.
>
> My test machine is a single CPU VM running FreeBSD 10 and PHP 5.5.9.  The
> largest test I ran was 100 nodes which was much fun to watch.
>
> ---
>
> One thing that I find seriously lacking, is the ability to identify a peer
> by IP address.  I've seen the recent patch for ZMQ_SRCFD, which will be
> handy in C and presumably in other languages as patches are made to the
> bindings.  I'm wondering, though, if the ROUTER and STREAM sockets couldn't
> be configured (perhaps by default) to providing some useful information in
> the identity string such as the descriptor, address family, address, port,
> and perhaps topic.
>
> One other thing that I'm wondering, if there couldn't be a low-level
> broadcast/flood mechanism built into the ROUTER/STREAM socket.  Sure, it's
> easy enough to iterate through all peers, but if I want to send the same
> message to several hundred peers, doing so at the lowest level in the 0MQ
> API should make the operation much less expensive.  Of course, not all peers
> will want to receive floods, so we would probably need a flag for that.
> Perhaps the first byte of the identity string could be used for flagging.
>
> 0x00 - Random 32bit ID  (current)
> 0x01 - Peer generated ID (minor change)
> 0x02 - Socket Info ID (added functionality)
> 0x04 - Can receive floods (capability flag)
> ...
> 0xFF - Broadcast a flood (sending only)
>
> All in all, I'm not even close to being up to speed in C/C++ to do this
> myself, mostly I'm just thinking about ways to extend functionality without
> incurring too much cost and hoping to catch someone's attention.  We would
> probably need much discussion to flesh these ideas out if it is to go
> anywhere at all.
>
> -Troy
>
>
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